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  • 1
    Publication Date: 2024-04-19
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The Ismenius Lacus region of Mars has a diverse geological history, and we present the first high‐resolution map of Deuteronilus Cavus (36.2°N; 14.0°E, ∼120 km diameter) in the fretted terrain south of the dichotomy boundary. Strong evidence suggests a volcanic origin of the regional plains, based on the ∼50 m thick volcanic bed underlying 180–300 m of sublimation residue associated with Amazonian plateau glaciation. Pervasive external volcanic flooding, internal erosional modification, and enlargement of a pre‐existing crater by up to 175%–200% resulted in the cavus' present shape. The phyllosilicates detected within Deuteronilus Cavus could be primary materials associated with the surficial aqueous activity, subsurface alteration products excavated by impacts, or a combination of both. We observe branching fluvial channels that are more recent than the traditional valley networks and may be related to fretted terrain resurfacing during the waning period of a high‐obliquity glaciation phase. This is consistent with our interpretation of the ∼600 m thick lobate and lineated deposits, which are remnants of receding glaciers. The glacial ice, protected by a 15–20 m insulating layer of debris cover, is of significant interest for future landing missions because of its potential to preserve biological and climatological signatures, to provide a critical test of Amazonian plateau glaciation, and to be used for in situ resource utilization. With our detailed geological mapping, we improved our understanding of the geological evolution and climatic conditions in the enigmatic fretted terrain near the dichotomy boundary.〈/p〉
    Description: Plain Language Summary: The ∼120 km long Deuteronilus Cavus was initiated by an impact event. The resulting impact crater was modified by glacial erosional and fluvial processes, leading to the enlargement of 175%–200% of the pre‐existing crater. In addition, we find strong evidence for recent glaciation (〈1 Ga) that left 180–300 m of sublimation residue on the plateau superimposed on a ∼50 m thick volcanic bed, suggesting a volcanic origin of the regional plains. During the waning period of a high‐glacial phase, the meltwater ponded on the surface of the cavus, altered surface rocks to produce phyllosilicates, formed channels (now observed as inverted sinuous ridges), and locally distributed branched fluvial channels that are more recent than the traditional valley networks. Glacial landforms still contain up to 600 m of remnant ice from the retreating glaciers at the end of the last glacial period. The relatively pure ice, protected by a 15–20 m insulating layer of debris cover, is critical for future landing missions because of its potential to preserve biological and climatological signatures and to be used for in situ resource utilization. Overall, this research enhances our understanding of the geological evolution and climatic history of Mars.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉We have produced the first high‐resolution map of Deuteronilus Cavus in the fretted terrain south of the Martian dichotomy boundary〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The region records a complex erosional and depositional history, including fluvial and glacial processes in the Amazonian period〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉This study provides a framework for exploration of high‐obliquity mid‐latitude plateau glaciation〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutsches Zentrum für Luft‐ und Raumfahrt http://dx.doi.org/10.13039/501100002946
    Description: https://doi.org/10.5281/zenodo.8205276
    Description: https://doi.org/10.17189/1520332
    Description: https://doi.org/10.17189/1520266
    Description: https://doi.org/10.17189/1520303
    Description: https://doi.org/10.5270/esa-pm8ptbq
    Keywords: ddc:523 ; Mars ; Deuteronilus Cavus ; geological mapping ; glaciation
    Language: English
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  • 2
    Publication Date: 2024-04-25
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Mercury is the smallest and innermost planet of our solar system and has a dipole‐dominated internal magnetic field that is relatively weak, very axisymmetric and significantly offset toward north. Through the interaction with the solar wind, a magnetosphere is created. Compared to the magnetosphere of Earth, Mercury's magnetosphere is smaller and more dynamic. To understand the magnetospheric structures and processes we use in situ MESSENGER data to develop further a semi‐empiric model of the magnetospheric magnetic field, which can explain the observations and help to improve the mission planning for the BepiColombo mission en‐route to Mercury. We present this semi‐empiric KTH22‐model, a modular model to calculate the magnetic field inside the Hermean magnetosphere. Korth et al. (2015, 〈ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1002/2015JA021022"〉https://doi.org/10.1002/2015JA021022〈/ext-link〉, 2017, 〈ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1002/2017gl074699"〉https://doi.org/10.1002/2017gl074699〈/ext-link〉) published a model, which is the basis for the KTH22‐model. In this new version, the representation of the neutral sheet current magnetic field is more realistic, because it is now based on observations rather than ad‐hoc assumptions. Furthermore, a new module is added to depict the eastward ring shaped current magnetic field. These enhancements offer the possibility to improve the main field determination. In addition, analyzing the magnetic field residuals allows us to investigate the field‐aligned currents and their possible dependencies on external drivers. We see increasing currents under more disturbed conditions inside the magnetosphere, but no clear dependence on the z‐component of the interplanetary magnetic field nor on the magnetosheath plasma 〈italic〉β〈/italic〉.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉We present a revised model of Mercury's magnetospheric magnetic field〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The model now includes an eastward ring shaped current and the neutral sheet current is calculated more precisely with Biot Savart's law〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The strength of the field‐aligned currents increases with higher magnetic activity〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: German Ministerium für Wirtschaft und Klimaschutz and the German Zentrum für Luft‐ und Raumfahrt
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: ESA Research Fellowship
    Keywords: ddc:523 ; Mercury ; magnetosphere ; field‐aligned currents ; modeling ; neutral sheet current ; planetary dipole moment
    Language: English
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  • 3
    Publication Date: 2024-04-25
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The seasonal deposition and sublimation of CO〈sub〉2〈/sub〉 constitute a major element in the Martian volatile cycle. Here, we propose to use the shadow variations of the ice blocks at the foot of the steep scarps of the North Polar Layered Deposits (NPLD) to infer the vertical evolution of the seasonal deposits. We conduct an experiment at a steep scarp centered at (85.0°N, 151.5°E). We assume that no snowfall remains on top of the selected ice blocks, the frost ice layer is homogeneous around the ice blocks and their surroundings, and no significant moating is present. We show that the average thickness of the seasonal deposits due to snowfalls in Mars Year 31 is 0.97 ± 0.13 m at Ls = 350.7° in late winter. The large depth measured makes us wonder if snowfalls are more frequent and violent than previously thought. Meanwhile, we show that the average frost thickness in Mars Year 31 reaches 0.64 ± 0.18 m at Ls = 350.7° in late winter. Combined, the total thickness of the seasonal cover in Mars Year 31 reaches 1.63 ± 0.22 m at Ls = 350.7° in late winter, continuously decreases to 0.45 ± 0.06 m at Ls = 42.8° in middle spring and 0.06 ± 0.05 m at Ls = 69.6° in late spring. These estimates are up to 0.8 m lower than the existing Mars Orbiter Laser Altimeter results during the spring. Meanwhile, we observe that snow in the very early spring of Mars Year 36 can be 0.36 ± 0.13 m thicker than that in Mars Year 31. This study demonstrates the dynamics of the Martian climate and emphasizes the importance of its long‐term monitoring.〈/p〉
    Description: Plain Language Summary: Like Earth, Mars also has seasons. Up to one third of the atmospheric CO〈sub〉2〈/sub〉 annually exchanges with the polar surface through seasonal deposition/sublimation processes. Deposition can be either atmospheric precipitation as snowfall or direct surface condensation as frost. At the steep scarps of the North Polar Layered Deposits (NPLD), fractured ice fragments can detach and fall to form ice blocks. We propose to use variations in the shadows of these ice blocks, observed in the High Resolution Imaging Science Experiment images, to infer the thickness evolution of the seasonal deposits. We make reasonable assumptions about the distribution of snowfall and frost around the ice blocks and their surroundings, which allow us to separately measure the thickness of snowfall and frost. Meanwhile, we introduce a novel approach that allows us to estimate the thickness of the seasonal deposits during late winter and early spring when image quality is insufficient. This approach also enables us to peer into the interannual thickness variations of snowfall. We carry out a successful experiment at a scarp centered at (85.0°N, 151.5°E). The obtained thickness measurements demonstrate the dynamics of the Martian volatile cycling and can be used to constrain the Martian climate models.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉We propose to examine the shadow variations of the ice blocks at the Martian polar region to infer the thickness of the seasonal deposits〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Maximum thickness of the seasonal deposits at the study scarp in MY31 is 1.63 ± 0.22 m to which snowfalls contribute 0.97 ± 0.13 m〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Seasonal deposits at the study scarp are up to 0.8 m shallower than previous measurements during spring〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: HX, LML, and PJG
    Description: https://doi.org/10.17189/1520303
    Description: https://doi.org/10.17632/5yy475dbry.1
    Description: https://doi.org/10.17632/x953mzxxvv.1
    Description: https://doi.org/10.17189/1520101
    Description: http://www.msss.com/moc_gallery/2001
    Keywords: ddc:523 ; Mars ; seasonal polar caps ; thickness ; ice blocks ; HiRISE ; CO2
    Language: English
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  • 4
    Publication Date: 2024-05-22
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Regardless of the steady increase of computing power during the last decades, numerical models in a 3D spherical shell are only used in specific setups to investigate the thermochemical convection in planetary interiors, while 2D geometries are typically favored in most exploratory studies involving a broad range of parameters. The 2D cylindrical and the more recent 2D spherical annulus geometries are predominantly used in this context, but the extent to how well they reproduce the 3D spherical shell results in comparison to each other and in which setup has not yet been extensively investigated. Here we performed a thorough and systematic study in order to assess which 2D geometry reproduces best the 3D spherical shell. In a first set of models, we investigated the effects of the geometry on thermal convection in steady‐state setups while varying a broad range of parameters. Additional thermal evolution models of three terrestrial bodies, namely Mercury, the Moon, and Mars, which have different interior structures, were used to compare the 2D and 3D geometries. Our investigations show that the 2D spherical annulus geometry provides results closer to models in a 3D spherical shell compared to the 2D cylindrical geometry. Our study indicates where acceptable differences can be expected when using a 2D instead of a 3D geometry and where to be cautious when interpreting the results.〈/p〉
    Description: Plain Language Summary: In geodynamic modeling, numerical models are used in order to investigate how the interior of a terrestrial planet evolves from the earliest stage, after the planetary formation, up to present day. Often, the mathematical equations that are used to model the physical processes in the interior of rocky planets are discretized and solved using geometric meshes. The most commonly applied geometries are the 3D spherical shell, the 2D cylinder, and the 2D spherical annulus. While being the most accurate and realistic, the 3D geometry is expensive in terms of computing power and time of execution. On the other hand, 2D geometries provide a reduced accuracy but are computationally faster. Here we perform an extensive comparison between 2D and 3D geometries in scenarios of increasing complexity. The 2D spherical annulus geometry shows much closer results to the 3D spherical shell when compared to the 2D cylinder and should be given preference in 2D modeling studies.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Interior dynamics models using the 2D spherical annulus geometry match the results of a 3D spherical shell better than the 2D cylinder〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The difference between 2D and 3D geometries decreases when models are heated from below by the core and from within by radioactive elements〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The 2D spherical annulus shows negligible differences to 3D for the thermal evolution of Mercury and the Moon, and acceptable values for Mars〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Ministry of Science, Research and the Arts Baden‐Württemberg
    Description: Federal Ministry of Education and Research
    Description: https://doi.org/10.5281/zenodo.8047757
    Keywords: ddc:523 ; mantle convection ; thermal evolution ; spherical annulus ; Mars ; Moon ; Mercury
    Language: English
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  • 5
    Publication Date: 2024-05-23
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉NASA's Juno mission delivered gravity data of exceptional quality. They indicate that the zonal winds, which rule the dynamics of Jupiter's cloud deck, must slow down significantly beyond a depth of about 3,000 km. Since the underlying inversion is highly non‐unique additional constraints on the flow properties at depth are required. These could potentially be provided by the magnetic field and its Secular Variation (SV) over time. However, the role of these zonal winds in Jupiter's magnetic field dynamics is little understood. Here we use numerical simulations to explore the impact of the zonal winds on the dynamo field produced at depth. We find that the main effect is an attenuation of the non‐axisymmetric field, which can be quantified by a modified magnetic Reynolds number Rm that combines flow amplitude and electrical conductivity profile. Values below Rm = 3 are required to retain a pronounced non‐axisymmetric feature like the Great Blue Spot (GBS), which seems characteristic for Jupiter's magnetic field. This allows for winds reaching as deep as 3,400 km. A SV pattern similar to the observation can only be found in some of our models. Its amplitude reflects the degree of cancellation between advection and diffusion rather than the zonal wind velocity at any depth. It is therefore not straightforward to make inferences on the deep structure of cloud‐level winds based on Jupiter's SV.〈/p〉
    Description: Plain Language Summary: The dynamics in Jupiter's cloud layer is dominated by eastward and westward directed wind jets that circumvent the planet and reach velocities of up to 150 m per second. For the first time, NASA's Juno mission could measure the tiny gravity changes caused by these winds. The data show that the winds reach down to a depth of about 3,000 km, roughly 4% of Jupiter's radius. However, the interpretation is difficult and several alternative wind profiles have been suggested. In this paper we use numerical simulations to explore how these winds would affect Jupiter's magnetic field, which has also been measured with high precision by Juno. The field shows a strong inward‐directed local patch just south of the equator, called the GBS. The impact of the winds on the magnetic field rapidly increases with depth because of the increase in the electrical conductivity. Our simulations show that winds reaching deeper than about 3,400 km would practically wipe out the GBS. This confirms that they have to remain shallower. Juno also observed an east‐ward drift of the GBS. While some of our simulations also show an east‐ward drift it is typically much too slow.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉We study the magnetic field variations caused by Jupiter's deep‐reaching surface winds for various flow and electrical conductivity models〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Zonal winds reaching deeper than 3,400 km would yield a very axisymmetric surface field and are thus unrealistic〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉It seems questionable that Jupiter's secular variation carries any useful information on the zonal winds〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Engineering and Physical Sciences Research Council http://dx.doi.org/10.13039/501100000266
    Description: https://doi.org/10.17617/3.CNVRWD
    Keywords: ddc:523 ; Jupiter ; magnetic field ; atmospheric dynamics ; zonal winds
    Language: English
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  • 6
    Publication Date: 2024-05-23
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The microphysical structure of the lunar regolith provides information on the geologic history of the Moon. We used remote sensing measurements of thermal emission and a thermophysical model to determine the microphysical properties of the lunar regolith. We expand upon previous investigations by developing a microphysical thermal model, which more directly simulates regolith properties, such as grain size and volume filling factor. The modeled temperatures are matched with surface temperatures measured by the Diviner Lunar Radiometer Experiment on board the Lunar Reconnaissance Orbiter. The maria and highlands are investigated separately and characterized in the model by a difference in albedo and grain density. We find similar regolith temperatures for both terrains, which can be well described by similar volume filling factor profiles and mean grain sizes obtained from returned Apollo samples. We also investigate a significantly lower thermal conductivity for highlands, which formally also gives a very good solution, but in a parameter range that is well outside the Apollo data. We then study the latitudinal dependence of regolith properties up to ±80° latitude. When assuming constant regolith properties, we find that a variation of the solar incidence‐dependent albedo can reduce the initially observed latitudinal gradient between model and Diviner measurements significantly. A better match between measurements and model can be achieved by a variation in intrinsic regolith properties with a decrease in bulk density with increasing latitude. We find that a variation in grain size alone cannot explain the Diviner measurements at higher latitudes.〈/p〉
    Description: Plain Language Summary: The Moon is covered by a layer of fine grained material called regolith. To extract information about the regolith, such as grain size or stratification, we used data from the Diviner instrument on board the Lunar Reconnaissance Orbiter. Diviner measures the surface temperature of the regolith for each location on the Moon and all times during day and night. To derive regolith properties, we developed a model and varied its model parameters until the simulated surface temperatures matched the measured ones. We applied the model up to a latitude of 80° and find as the best solution a decrease in regolith packing density with increasing latitude. We also find that a variation of regolith grain size alone cannot explain the measurements. These predictions are valuable for planning future missions targeting higher latitudes and can be compared with future in situ measurements and returned samples. However, the fraction of sunlight that actually heats the regolith is quite unknown, especially at high latitudes. A variation of this fraction can explain the measured surface temperatures reasonably well even without a variation of the regolith properties with latitude.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉We developed a microphysical thermal model accounting for regolith grain size and volume filling factor〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The best match between model and Lunar Reconnaissance Orbiter/Diviner data was achieved with a decrease in bulk density between 30° and 80° latitude〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉We also found a reasonable agreement between observed and modeled surface temperatures when varying the solar incidence dependent albedo〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: LRO project
    Description: https://doi.org/10.17189/WJ0S-W188
    Description: https://doi.org/10.5281/zenodo.8433837
    Description: https://doi.org/10.5281/zenodo.10781188
    Keywords: ddc:523 ; Moon ; regolith ; Diviner ; thermal modeling ; lunar
    Language: English
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  • 7
    Publication Date: 2024-05-23
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Teleseismic back‐projection imaging has emerged as a powerful tool for understanding the rupture propagation of large earthquakes. However, its application often suffers from artifacts related to the receiver array geometry. We developed a teleseismic back‐projection technique that can accommodate data from multiple arrays. Combined processing of P and pP waveforms may further improve the resolution. The method is suitable for defining arrays ad‐hoc to achieve a good azimuthal distribution for most earthquakes. We present a catalog of short‐period rupture histories (0.5–2.0 Hz) for all earthquakes from 2010 to 2022 with 〈italic〉M〈/italic〉〈sub〉〈italic〉W〈/italic〉〈/sub〉 ≥ 7.5 and depth less than 200 km (56 events). The method provides automatic estimates of rupture length, directivity, speed, and aspect ratio, a proxy for rupture complexity. We obtained short‐period rupture length scaling relations that are in good agreement with previously published relations based on estimates of total slip. Rupture speeds were consistently in the sub‐Rayleigh regime for thrust and normal earthquakes, whereas a tenth of strike‐slip events propagated at supershear speeds. Many rupture histories exhibited complex behaviors, for example, rupture on conjugate faults, bilateral propagation, and dynamic triggering by a P wave. For megathrust earthquakes, ruptures encircling asperities were frequently observed, with downdip, updip, and balanced patterns. Although there is a preference for short‐period emissions to emanate from central and downdip parts of the megathrust, emissions updip of the main asperity are more frequent than suggested by earlier results.〈/p〉
    Description: Plain Language Summary: Back‐projection is an earthquake imaging method based on seismic waveforms recorded remotely at a group of seismometers (seismic array). Here, we develop a new approach to combine backprojections from multiple arrays and seismic waveforms and use it to derive a catalog of large earthquake rupture histories from 2010 to 2022, providing a map view of the high‐frequency radiation emitted along the fault. The method automatically estimates the earthquake rupture length, speed, directivity, and aspect ratio. Based on these estimates, we obtained scaling relations between the earthquake magnitude and rupture length that agree with classical relationships. We identified strike‐slip earthquakes propagating at supershear, that is, faster than the shear wave speed, the usual limit for self‐sustaining rupture propagation. We observed complex rupture behaviors, for example, multiple faults activated, bilateral ruptures, and triggering of the main phase of a rupture by a primary (P) wave from the earliest part of the rupture. For subduction earthquakes, high‐frequency emissions were often observed, forming a ring around the fault interface patches (asperities) where the main slip occurs. There was a preference for high‐frequency radiation to emanate from central and deeper parts of the subducting plate interface, but shallower emissions were more frequent than expected from previous literature.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉We provide a complete catalog of high‐frequency rupture histories for 〈italic〉M〈/italic〉 ≥ 7.5 events 2010–2022〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉We develop a semi‐automatic method for estimating rupture length, speed, directivity, and aspect ratio〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Both encircling ruptures and emissions updip of slip asperities common in megathrust earthquakes〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: National Agency for Research and Development (ANID)
    Description: https://doi.org/10.5880/GFZ.2.4.2024.001
    Keywords: ddc:551.22 ; back‐projection ; megathrust earthquakes ; complex ruptures ; supershear ruptures ; scaling relations ; earthquake rupture catalog
    Language: English
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  • 8
    Publication Date: 2023-09-13
    Description: At the Blanco transform fault system (BTFS) off Oregon, 138 local earthquakes and 84 double‐couple focal mechanisms from ocean‐bottom‐seismometer recordings jointly discussed with bathymetric features reveal a highly segmented transform system without any prominent fracture zone traces longer than 100 km. In the west, seismicity is focused at deep troughs (i.e., the West and East Blanco, and Surveyor Depressions). In the east, the BTFS lacks a characteristic transform valley and instead developed the Blanco Ridge, which is the most seismically active feature, showing strike‐slip and dip‐slip faulting. Sandwiched between the two main segments of the BTFS is the Cascadia Depression, representing a short intra‐transform spreading segment. Seismic slip vectors reveal that stresses at the eastern BTFS are roughly in line with plate motion. In contrast, stresses to the west are clockwise skewed, indicating ongoing reorganization of the OTF system. As we observed no prominent fracture zones at the BTFS, plate tectonic reconstructions suggest that the BTFS developed from non‐transform offsets rather than pre‐existing transform faults during a series of ridge propagation events. Our observations suggest that the BTFS can be divided into two oceanic transform systems. The eastern BTFS is suggested to be a mature transform plate boundary since ∼0.6 Ma. In contrast, the western BTFS is an immature transform system, which is still evolving to accommodate far‐field stress change. The BTFS acts as a natural laboratory to yield processes governing the development of oceanic transform faults.
    Description: Plain Language Summary: The Blanco transform fault system (BTFS) northwest off the coast of Oregon is seismically very active. We used 1 year of ocean bottom seismometer data collected between September 2012 and October 2013 to locate 138 local earthquakes. The events align perfectly with the morphologic features of the BTFS, dividing the BTFS into five transform segments and two short intra‐transform spreading centers. Furthermore, we observe different seismotectonic behaviors of the western and eastern BTFS based on the along‐strike variation in morphology, magnetization, focal depth distribution, and strain partitioning. Although many segmented oceanic transform systems were formed from a single transform fault in response to rotations in plate motion, the BTFS turns out to be originated from non‐transform offsets between ridge segments, as we observed no prominent fracture zone traces neither in morphology nor gravity field data. A clockwise shift in the Juan de Fuca/Pacific pole of rotation at ∼5 Ma followed by a series of ridge propagation events initiated the formation of the BTFS, integrated each segment of the BTFS by shortening the ridge segments in between. Our observations suggest that the Blanco Ridge and the Gorda transform segment in the eastern BTFS were formed at ∼1.6 and 0.6 Ma, respectively, and ever since, the eastern BTFS became a mature transform boundary. In contrast, seismic slip vectors comparing to plate motion directions reveal that stresses in the western BTFS are systematically skewed, suggesting the immature transform plate boundary is still adjusting to the new stress regime.
    Description: Key Points: Local seismicity of the Blanco transform fault system (BTFS) reveals along‐strike variations dominated by strike‐slip and oblique dip‐slip. The BTFS developed from non‐transform offsets rather than discrete transform faults in response to plate rotation and ridge propagation. The BTFS consists of a mature plate boundary in the east and an immature system in the west, separated by a central spreading center.
    Description: China Scholarship Council http://dx.doi.org/10.13039/501100004543
    Description: https://doi.org/10.7914/SN/X9_2012
    Description: https://www.gmrt.org/GMRTMapTool/
    Description: https://mrdata.usgs.gov/magnetic/
    Keywords: ddc:551.22 ; Blanco transform fault system ; local seismicity ; tectonic evolution ; transform plate boundary
    Language: English
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  • 9
    Publication Date: 2023-09-13
    Description: The Martian magnetosphere contains elements of induced and intrinsic origin. To display them one must use different coordinate systems. Although the solar‐electric coordinate system (Mars Solar Electric [MSE]) adequately describes the main features of the induced magnetosphere, it removes/suppresses aspects caused by the crustal magnetic sources while rotating the spacecraft position to the MSE‐coordinate system and averaging over many orbits. On the other hand, to observe effects of the crustal field one should use the solar orbital coordinates (Mars Solar Orbital [MSO]). To find a compromise and keeping in mind that the most probable value of the clock angle of the interplanetary magnetic field (IMF) on the Mars orbit is ∼90° we can consider separately cases with positive and negative B〈sub〉y〈/sub〉 components of the IMF. It is shown that dynamics of ion fluxes in the distant regions of the magnetosphere is mainly controlled by induced features. However, reconnection of the draping IMF with crustal field leads to a twisting of the classical draping configuration. Despite of the very intricate local geometry of the crustal field, the low‐order harmonics of the magnetic field and mainly the dipole component determine the reconnection sites, at least, statistically for many Mars rotations. For different signs of the By component of the IMF these sites occur either in the +Y‐MSO or −Y‐MSO hemispheres. As a result, statistically the magnetosphere of Mars looks like a hybrid magnetosphere formed during the solar wind interaction with the obstacle which simultaneously contains an extended ionosphere and a weak dipole magnetic field.
    Description: Key Points: The Martian magnetosphere contains elements of induced and intrinsic origin. Dynamics of ion fluxes in the magnetic tail, is mainly controlled by induced features. Reconnection of the interplanetary magnetic field with low‐order harmonics of the crustal field leads to twisting of the tail and formation of hybrid magnetosphere.
    Description: DFG
    Description: https://pds-ppi.igpp.ucla.edu/mission/MAVEN
    Keywords: ddc:523 ; Martian magnetosphere
    Language: English
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  • 10
    Publication Date: 2023-11-27
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉For the first time, we measured the ellipticity of direct Rayleigh waves at intermediate periods (15–35 s) on Mars using the recordings of three large seismic Martian events, including S1222a, the largest event recorded by the InSight mission. These measurements, together with P‐to‐s receiver functions and P‐wave reflection times, were utilized for performing a joint inversion of the local crustal structure at the InSight landing site. Our inversion results are compatible with previously reported intra‐crustal discontinuities around 10 and 20 km depths, whereas the preferred models show a strong discontinuity at ∼37 km, which is interpreted as the crust‐mantle interface. Additionally, we support the presence of a shallow low‐velocity layer of 2–3 km thickness. Compared to nearby regions, lower seismic wave velocities are derived for the crust, suggesting a higher porosity or alteration of the whole local crust.〈/p〉
    Description: Plain Language Summary:: As never before on Mars, we measured the characteristics of seismic waves traveling along the Martian surface that carry information about the crustal structure at the InSight site. We combined these measurements with two other local‐scale independent observations to derive a consolidated model for the crust underneath the InSight lander. Our results suggest a Martian crust with 4 layers and, particularly, one thin layer of about 2 km thickness close to the surface. The crust‐mantle discontinuity was found at ∼37 km depth, where the sharpest change in seismic wave velocity is observed. Overall, the seismic wave velocities of the local Martian crust at the InSight site are lower than those derived in other regions on Mars, which suggests a higher porosity or local alteration.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Rayleigh waves ellipticity was measured between periods 15–35 s at the InSight landing site using large seismic events, including S1222a〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉A 4‐layer crust, including a shallow low‐velocity layer, is required to explain the ellipticity, receiver functions and P‐wave lag times〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Low crustal velocities are derived for the InSight site, which may be due to high porosity or heavy alteration at local scale〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: National Aeronautics and Space Administration
    Description: Agence Nationale de la Recherche http://dx.doi.org/10.13039/501100001665
    Description: https://doi.org/10.12686/a19
    Description: https://doi.org/10.18715/SEIS.INSIGHT.XB_2016
    Description: https://doi.org/10.7914/SN/BQ
    Description: https://www.globalcmt.org/CMTsearch.html
    Description: https://github.com/scarrascom/Rellipy
    Description: https://doi.org/10.5281/zenodo.8051337
    Description: http://www.geopsy.org/
    Keywords: ddc:523 ; martian crust ; marsquakes ; Rayleigh waves ellipticity ; receiver functions
    Language: English
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  • 11
    Publication Date: 2023-12-12
    Description: Strain energy from tectonic loading can be partly released through aseismic creep. Earthquake repeaters, repeatedly activated brittle fault patches surrounded by creep, indicate steady‐state creep that affects the amount of seismic energy available for the next large earthquake along a plate contact. The offshore Main Marmara Fault (MMF) of the North Anatolian Fault Zone represents a seismic gap capable of generating a M 〉 7 earthquake in direct vicinity to the mega‐city Istanbul. Based on a newly compiled seismicity catalog, we identify repeating earthquakes to resolve the spatial creep variability along the MMF during a 15‐year period. We observe a maximum of seismic repeaters indicating creep along the central and western MMF segments tapering off toward the locked onshore Ganos fault in the west, and the locked offshore Princes Islands segment immediately south of Istanbul in the east. This indicates a high degree of spatial creep variability along the Istanbul‐Marmara seismic gap.
    Description: Plain Language Summary: The relative motion of tectonic plates deforms these plates along their contact zone until the plate contact ruptures in an earthquake. However, some of this deformation can be released without earthquakes by so‐called aseismic creep in which the plates creep past each other. Within this creep zone, sometimes some brittle patches exist that interlock during the plate creep and rupture repeatedly in smaller earthquakes that are very similar. They are called earthquake repeaters. In the Sea of Marmara south of Istanbul lies the contact between the Eurasian and the Anatolian plates, the so‐called Main Marmara Fault (MMF). This plate contact did not rupture for a long time and thus a large magnitude event is expected here. We observe a large number of earthquake repeaters in the western offshore part of the MMF while no earthquake repeaters are found toward the east south of Istanbul or onshore toward the west. These areas seem to be locked and might accumulate deformation for a future large earthquake. The zones in between show an intermediate behavior with fewer earthquake repeaters indicating less creep. These results are important for the seismic risk and hazard assessment for the mega‐city of Istanbul.
    Description: Key Points: Earthquake repeaters along the Main Marmara Fault are identified based on a newly derived homogeneous earthquake catalog spanning 15 years. Seismic creep estimated from these repeaters is highly variable along‐strike with higher creep values along the western part. A repeating earthquake sequence showing accelerated activity after a nearby Mw 5.2 earthquake is observed.
    Description: Helmholtz Association http://dx.doi.org/10.13039/501100009318
    Description: https://doi.org/10.5880/GFZ.4.2.2023.002
    Description: http://doi.org/10.7914/SN/TU
    Description: http://doi.org/10.7914/SN/KO
    Description: http://doi.org/10.7914/SN/PZ
    Description: http://doi.org/10.7914/SN/TB
    Description: http://alomax.free.fr/nlloc/
    Description: https://www.ldeo.columbia.edu/%7Efelixw/hypoDD.html
    Description: http://doi.org/10.5281/zenodo.3407866
    Description: https://doi.org/10.1029/2019gc008515
    Keywords: ddc:551.22 ; repeating earthquakes ; Marmara Sea ; fault creep ; seismic cyle ; seismic gap
    Language: English
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  • 12
    Publication Date: 2023-10-26
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Planetary impacts have shaped the surfaces and interiors of planets. They were particularly critical in the last stage of planetary accretion, as they have eventually formed terrestrial planets. During these large supersonic collisions, shock waves melted the impactor and the target, and formed silicate magma oceans. Because the propagation of shock waves and the melting is faster than the excavation of an impact crater, the cratering stage can be considered as a purely hydrodynamic process. Here, we use both laboratory impact experiments in water and numerical simulations to investigate the crater dimensions resulting from the impact of a liquid impactor onto a liquid target. We show that our numerical models reproduce the laboratory experiments at subsonic impact velocities. We then explore the effect of both the Froude number, which is the ratio of the impactor kinetic energy to gravity, and the Mach number, which is the ratio of the impact speed to the sound speed. We vary these two parameters independently in impact simulations, going from subsonic to supersonic conditions. We obtain a new scaling law for the crater dimensions that describes the transition from subsonic to supersonic impacts. Our results indicate that the transition between these two regimes results from a change in the partitioning of the impactor kinetic energy into potential energy in the crater and internal energy. Finally, our scaling suggests that, in the limit of large Mach numbers, the crater depth depends only on the sound velocity and gravity, and is independent of the impact speed.〈/p〉
    Description: Plain Language Summary: Planetary formation involved a large number of very energetic collisions. Such impacts generated shock waves which led to widespread melting and the formation of magma oceans. Understanding the dynamics of impacts into magma oceans is of great importance as these collisions set the initial temperature and composition of terrestrial planets and satellites. Laboratory experiments and numerical simulations have been used to investigate large impacts. However, each approach has pros and cons. Liquid impact experiments can produce the small scales responsible for the mixing between the impactor and the target, but they fail to reproduce shock waves and supersonic speeds. In contrast, current numerical simulations reach supersonic conditions but produce a limited amount of turbulence and mixing. In this study, we bridge the gap between these two methods and improve our understanding of the effect of the impact velocity on the cratering process. Using the code iSALE, we numerically reproduce water impact experiments at low subsonic velocities. We then explore supersonic conditions in impact simulations. We obtain a new scaling law predicting the crater depth in more realistic impact conditions and show that it is limited only by the sound speed for large impact velocities.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉The shock physics code iSALE is successfully benchmarked against subsonic water impact experiments〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉A scaling law is proposed for the crater depth as a function of the Mach and Froude numbers which are varied as independent parameters〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉In the limit of high Mach numbers, our scaling suggests that the maximum crater depth is controlled by the sound velocity and gravity, but not by the impact speed〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: DFG
    Description: EPSRC
    Description: National Aeronautics and Space Administration
    Description: NSF Physics Frontier Center
    Description: Programme National de Planétologie
    Description: CNES
    Description: Alfred P. Sloan Foundation
    Description: https://isale-code.github.io/
    Keywords: ddc:523 ; impact cratering ; pi‐scaling ; magma ocean ; scaling laws ; fluid dynamics
    Language: English
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  • 13
    Publication Date: 2023-12-16
    Description: We report on observations made by the Mars Atmosphere and Volatile EvolutioN spacecraft at Mars, in the region of the ion plume. We observe that in some cases, when the number density of oxygen ions is comparable to the density of the solar wind protons interaction between both plasmas leads to formation in the magnetosheath of mini induced magnetospheres possessing all typical features of induced magnetospheres typically observed at Mars or Venus: a pileup of the magnetic field at the head of the ion cloud, magnetospheric cavity, partially void of solar wind protons, draping of the interplanetary magnetic field around the mini obstacle, formation of a magnetic tail with a current sheet, in which protons are accelerated by the magnetic field tensions. These new observations may shed a light on the mechanism of formation of induced magnetospheres.
    Description: Plain Language Summary: There is a class of the induced planetary magnetospheres when the absence of intrinsic magnetic field allows a direct interaction of solar wind with planetary atmospheres/ionospheres. We have shown the existence of mini‐induced magnetospheres at Mars. When the density of the extracted from the ionosphere oxygen ions becomes comparable with the proton density in solar wind mini‐induced magnetospheres with all typical features of the planetary induced magnetospheres arise.
    Description: Key Points: Oxygen ions extracted from the Martian ionosphere interact with shocked solar wind in the magnetosheath. When the ion densities of both plasmas become comparable the mini induced magnetospheres are built. These Magnetospheres possess all typical features of the classical induced magnetospheres.
    Description: NASA
    Description: DFG
    Description: https://pds-ppi.igpp.ucla.edu/mission/MAVEN/MAVEN/MAG
    Description: https://pds-ppi.igpp.ucla.edu/mission/MAVEN/MAVEN/STATIC
    Keywords: ddc:523 ; Mars ; solar wind ; induced magnetosphere ; ionosphere ; magnetic barrier ; magnetic tail
    Language: English
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  • 14
    Publication Date: 2023-12-15
    Description: The lithosphere of the Moon has been deformed by tectonic processes for at least 4 billion years, resulting in a variety of tectonic surface features. Extensional large lunar graben formed during an early phase of net thermal expansion before 3.6 Ga. With the emplacement of mare basalts at ∼3.9–4.0 Ga, faulting and folding of the mare basalts initiated, and wrinkle ridges formed. Lunar wrinkle ridges exclusively occur within the lunar Maria and are thought to be the result of superisostatic loading by dense mare basalts. Since 3.6 Ga, the Moon is in a thermal state of net contraction, which led to the global formation of small lobate thrust faults called lobate scarps. Hence, lunar tectonism recorded changes in the global and regional stress fields and is therefore an important archive for the thermal evolution of the Moon. Here, we mapped tectonic features in the non‐mascon basin Mare Tranquillitatis and classified these features according to their respective erosional states. This classification aims to provide new insights into the timing of lunar tectonism and the associated stress fields. We found a wide time range of tectonic activity, ranging from ancient to recent (3.8 Ga to 〈50 Ma). Early wrinkle ridge formation seems to be closely related to subsidence and flexure. For the recent and ongoing growth of wrinkle ridges and lobate scarps, global contraction with a combination of recession stresses and diurnal tidal stresses, as well as with a combination of South Pole‐Aitken ejecta loading and true polar wander are likely.
    Description: Plain Language Summary: The lithosphere of the Moon has been deformed by tectonic processes for at least 4 billion years, resulting in a variety of tectonic surface features. Simple compressional asymmetric landforms are called lobate scarps and complex compressional features, which form as a result of the combination of faulting and folding, are known as wrinkle ridges. Lunar wrinkle ridges only occur within the lunar Maria. It has been argued that their formation is linked to the subsidence of the dense mare basalts, which would have happened in the early history of the Moon. We mapped all of these features within a dark lunar region called Mare Tranquillitatis and then studied their morphology on high‐resolution images. Based on their morphology, we found a wide time range of tectonic activity, ranging from ancient to recent. Large wrinkle ridges seem to be ancient and influenced by subsidence. Smaller wrinkle ridges and lobate scarps show signs of recent activity. They likely formed recently within the last hundred million years because of the Moon's current state of global compression.
    Description: Key Points: Early compressional tectonism in Tranquillitatis, in the form of wrinkle ridges, is presumably related to subsidence and basin loading. Later tectonism could reflect the evolution from a basin‐localized to a global stress field and the continued growth of ancient faults. Recent wrinkle ridge and lobate scarp formation in Tranquillitatis occurred in the last 50 Ma and is influenced by a global stress field.
    Description: https://doi.org/10.5281/zenodo.7551409
    Description: https://darts.isas.jaxa.jp/planet/pdap/selene/
    Description: https://doi.org/10.17189/1520341
    Description: http://imbrium.mit.edu/DATA/SLDEM2015
    Description: https://doi.org/10.17189/1519529
    Description: https://quickmap.lroc.asu.edu/
    Description: http://www.yongtechnology.com/download/georose
    Keywords: ddc:523 ; Moon ; tectonics ; wrinkle ridges ; lobate scarps ; lithosphere ; tectonic mapping
    Language: English
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  • 15
    Publication Date: 2023-12-14
    Description: Laser‐induced breakdown spectroscopy, as utilized by the ChemCam instrument onboard the Curiosity rover, detected enhanced abundances of the element copper. Since landing in Gale crater (6 August 2012), 10 enhancements in copper abundance were observed during 3007 Martian days (sols) of rover operations and 24 km of driving (as of 20 January 2021). The most prominent ones were found in the Kimberley area on the crater floor (Aeolis Palus) and in Glen Torridon (GT) on the lower flanks of Aeolis Mons (Mt. Sharp). Enhancements in copper record the former existence of modestly acidic and oxidizing fluids, which were more oxidizing in Kimberley than in GT. Of the two main types of bedrock in the lowest part of GT, Mg‐rich “coherent” and K‐rich “rubbly” (named based on their outcrop expression), copper was detected only in coherent, not in rubbly bedrock. The difference between these two types of bedrock may be due to difference in provenance. Alternatively, based on a recently developed lacustrine‐groundwater mixing model, we suggest that rubbly bedrock was altered by modestly acidic, shallow‐subsurface lake water that leached out both copper and manganese, while coherent bedrock was affected by dominantly alkaline fluids which would be consistent with its mineralogical composition (including siderite) as returned by the CheMin instrument onboard the rover. Higher up in GT, ChemCam data indicated significant gradients in the copper concentration in coherent bedrock on a local scale of only a few meters, which suggests a different alteration style and possibly different types of diagenetic fluids.
    Description: Plain Language Summary: Gale crater, Mars, about 152‐km in diameter and 3.6 Ga in age, has a central mound that is partly of sedimentary origin. To date (July 2022), the NASA rover Curiosity has been exploring the crater floor and the lower‐most 600 m (in elevation) of sediments of that mound. ChemCam, an instrument mounted on top of the remote‐sensing mast utilizing Laser‐Induced Breakdown Spectroscopy, has been measuring chemical composition and specifically copper abundances along the rover traverse. We identified 10 areas of copper enhancement along Curiosity's traverse. In the Kimberley formation on the crater floor, copper was identified in a manganese‐rich sandstone. Later on, some 350 m above Kimberley, high copper abundances were detected in magnesium‐rich mudstone and in iron‐rich sandstone in the Jura and Knockfarril Hill member, respectively. Following earlier work about copper in Gale crater (Payré et al., 2019, https://doi.org/10.1016/j.icarus.2018.12.015), we postulate a copper‐rich source region north of Gale crater and suggest that copper‐rich detrital material delivered to these areas in Gale crater. Taking into account the chemical and mineralogical composition of these types of bedrock, we conclude that copper was mobilized by later acidic and oxidizing fluids.
    Description: Key Points: High copper abundances (200–400 ppm) are found in specific areas along the rover traverse. In the Jura member in Glen Torridon (GT), copper is detected only in coherent bedrock, not in rubbly bedrock. In the Knockfarril Hill member in GT, there is evidence for the redistribution of copper and iron by acidic, oxidizing fluids.
    Description: DFG
    Description: NASA Mars Exploration Program
    Description: CNES
    Description: CNRS
    Keywords: ddc:523 ; Mars ; copper ; diagenesis ; Gale crater ; ChemCam ; Curiosity rover
    Language: English
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  • 16
    Publication Date: 2024-01-12
    Description: Thematic map creation is a meticulous process that requires several steps to be accomplished regardless of the type of map to be produced, from data collection, through data exploitation and map publication in print, image, and GIS format. Examples are geolithological, and geomorphological maps in which most of the highest time‐consuming tasks are those related to the discretization of single objects. Introducing also interpretative biases because of the different experience of the mappers in identifying a set of unique characteristics that describe those objects. In this setting, Deep Learning Computer Vision techniques could play a key role but lack the availability of a complete set of tools specific for planetary mapping. The aim of this work is to develop a comprehensive set of ready‐to‐use tools for landforms mapping based on validated Deep Learning methodologies and open‐source libraries. We present DeepLandforms, the first pre‐release of a toolset for landform mapping using Deep Learning that includes all the components for data set preparation, model training, monitoring, and inference. In DeepLandforms, users have full access to the workflow and control over all the processes involved, granting complete control and customization capabilities. In order to validate the applicability of our tool, in this work we present the results achieved using DeepLandforms in the science case of mapping sinkhole‐like landforms on Mars, as a first example that can lead us into multiple and diverse future applications.
    Description: Plain Language Summary: The creation of maps is a complex set of several tasks that, regardless of the type of map, are often very time‐consuming. For instance, all the occurrences of a specific object, natural or man‐made in a defined area, need to be identified, drawn and classified manually. Mapping large objects in small areas is an easy task but may be unmanageable in cases such as small landforms on the entire surface of a planet. Nowadays, especially on Earth, researchers and professionals take advantages of highly specialized software based on a technique called Deep Learning. Such software are almost never free nor ready‐to‐use and often requires higher knowledge in computer programming languages. In this work, we present the first pre‐release of a novel open‐source computer software, nearly ready‐to‐use, that provides all the instruments for approaching Deep Learning for automatic landforms mapping. We present also the results obtained by trying this software using data of Mars's surface to map sinkhole‐like landforms.
    Description: Key Points: Instance Segmentation methodology is used to map landforms obtaining vectorial data in geopackage file format. A newly developed composite toolset to perform image pre‐processing, data labeling, model training and inference tasks is presented. The results of a prime case of mapping pit and skylights on Mars surface are showed.
    Description: European Union's Horizon 2020 research and innovation programme
    Description: https://doi.org/10.5281/zenodo.7351391
    Description: https://doi.org/10.5281/zenodo.7488867
    Description: https://ode.rsl.wustl.edu/odeholdings/Mars_holdings.html
    Keywords: ddc:523 ; mapping ; Mars ; pits ; skylight ; deep learning ; toolset
    Language: English
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  • 17
    Publication Date: 2023-07-20
    Description: The seismic activity of a planet can be described by the corner magnitude, events larger than which are extremely unlikely, and the seismic moment rate, the long‐term average of annual seismic moment release. Marsquake S1222a proves large enough to be representative of the global activity of Mars and places observational constraints on the moment rate. The magnitude‐frequency distribution of relevant Marsquakes indicates a $b$‐value of 1.06. The moment rate is likely between $1.55\times {10}^{15}\mathrm{N}\mathrm{m}/\mathrm{a}$ and $1.97\times {10}^{18}\mathrm{N}\mathrm{m}/\mathrm{a}$, with a marginal distribution peaking at $4.9\times {10}^{16}\mathrm{N}\mathrm{m}/\mathrm{a}$. Comparing this with pre‐InSight estimations shows that these tended to overestimate the moment rate, and that 30% or more of the tectonic deformation may occur silently, whereas the seismicity is probably restricted to localized centers rather than spread over the entire planet.
    Description: Plain Language Summary: The seismic moment rate is a measure for how fast quakes accumulate deformation of the planet's rigid outer layer, the lithosphere. In the past decades, several models for the deformation rate of Mars were developed either from the traces quakes leave on the surface, or from mathematical models of how quickly the planet's interior cools down and shrinks. The large marsquake that occurred on the 4th of May 2022 now allows a statistical estimation of the deformation accumulated on Mars per year, and thus to confront these models with reality. It turns out that, although there is a considerable overlap, the models published prior to InSight tend to overestimate the seismic moment rate, and hence the ongoing deformation on Mars. Possible explanations are that 30% or more of the deformation occurs silently, that is, without causing quakes, or that not the entire planet is seismically active but only specific regions.
    Description: Key Points: A single large marsquake suffices to constrain the global seismic moment rate. Pre‐InSight estimations tended to overestimate the moment rate. Either a significant part of the ongoing deformation occurs silent, or seismic activity is restricted to some activity centers, or both.
    Description: Eidgenössische Technische Hochschule Zürich http://dx.doi.org/10.13039/501100003006
    Description: National Aeronautics and Space Administration http://dx.doi.org/10.13039/100000104
    Description: UK Space Agency http://dx.doi.org/10.13039/100011690
    Description: Deutsches Zentrum für Luft‐ und Raumfahrt http://dx.doi.org/10.13039/501100002946
    Description: Insight SFI Research Centre for Data Analytics http://dx.doi.org/10.13039/501100021525
    Description: http://dx.doi.org/10.18715/SEIS.INSIGHT.XB_2016
    Description: http://doi.org/10.17189/1517570
    Keywords: ddc:523 ; Mars ; InSight ; seismic moment rate ; S1222a
    Language: English
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  • 18
    Publication Date: 2023-07-27
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Results from the Cassini‐Huygens space mission at Enceladus revealed a substantial inventory of organic species embedded in plume and E ring ice grains originating from a global subsurface and putative habitable ocean. Compositional analysis by the Cosmic Dust Analyzer indicated the presence of aromatic species and constrained some structural features, although their exact nature remains unclear. As indicated by many studies, among other organic species, low‐mass aromatics likely played a role in the emergence of life on Earth and may be linked to potential prebiotic or biogenic chemistry on icy moons. Here, we study the behavior of single‐ringed aromatic compounds—benzoic acid and two isomeric derivatives, 2,3‐dihydroxybenzoic acid and 2,5‐dihydroxybenzoic acid—using Laser‐Induced Liquid Beam Ion Desorption (LILBID), an analogue setup to simulate the impact ionization mass spectra of ice grains in space. These compounds share common structural features but also exhibit differences in functional groups and substituent positions. We investigate the fragmentation behavior and spectral appearance of each molecule over three simulated impact velocities, in both positive and negative ion modes. Parent compounds can be distinguished easily from their derivatives due to various spectral differences, including the (de)protonated molecular ion peaks appearing at different 〈italic〉m〈/italic〉/〈italic〉z〈/italic〉 values. We conclude that distinction between structural isomers in LILBID is more challenging, but some insights can be revealed by considering intermolecular bonding regimes. This work will guide future investigations into elucidating the composition of isomeric biosignatures in ice grains, relevant for future space missions to Enceladus and Europa.〈/p〉
    Description: Plain Language Summary: The Cassini‐Huygens space mission discovered a plume at Enceladus that ejects gases and frozen ice grains originating from an ocean of liquid water below its icy shell. In these ice grains, a range of interesting organic molecules were discovered by Cassini's Cosmic Dust Analyzer mass spectrometer. Organic molecules are important in the search for life beyond Earth as they form the basis of all known Earth life, and active biology elsewhere would likely have a discernible effect on the local inventory of organic species. One class of organic, with a ring structure of carbon atoms, called aromatics, were discovered in the plume. We investigate the spectral appearance of one example of aromatic compound, benzoic acid, as well as two similar compounds with additional chemical groups attached to the aromatic ring. The two similar compounds have the same mass and general structure, but slightly different arrangements of the additional groups, known as isomers. We find that it is simple to distinguish mass spectral features between benzoic acid and its related compounds, but more difficult to explain the differences between the isomers. This work will assist the analysis of mass spectrometry data from future habitability‐investigating space missions to ocean‐bearing icy moons.〈/p〉
    Description: Key Points: Cassini revealed a variety of organic compounds including clear evidence of aromatics in the plume of Enceladus. Identifying mass spectral features of isomeric organics enhances our ability to assess the astrobiological potential of Enceladus/Europa. Parent aromatic compounds can be easily distinguished from their derivatives in ice grains with impact ionization mass spectrometry.
    Description: European Research Council Consolidator
    Description: http://dx.doi.org/10.17169/refubium-37960
    Description: https://lilbid-db.planet.fu-berlin.de/
    Keywords: ddc:523 ; mass spectrometry ; LILBID and impact ionization ; aromatics and isomeric derivatives ; Enceladus and Europa ; space missions ; habitability
    Language: English
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  • 19
    Publication Date: 2023-07-27
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The Radiation Assessment Detector (RAD) on board the Mars Science Laboratory's Curiosity rover has been monitoring the surface radiation environment on Mars for just over 10 years. It has been found by Wimmer‐Schweingruber et al. (2015, 〈ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1002/2015gl066664"〉https://doi.org/10.1002/2015gl066664〈/ext-link〉) that within the narrow view cone of RAD, the directionality of the radiation field is close to but not completely isotropic. In order to better understand the directionality of the surface radiation over a wide range of zenith angles (〈italic〉θ〈/italic〉), we perform a three‐dimensional Geant4 Monte Carlo simulation to derive the 〈italic〉θ〈/italic〉‐dependence of the surface dose rate. The results show that galactic cosmic ray protons, coming in at 〈italic〉θ〈/italic〉 ∼ 74° make the greatest contribution to the surface dose. For helium ions, this angle is at around 46°. This is a consequence of the increasing column depth at larger zenith angles and the complex interplay of the destruction of primary and the creation of secondary particles as the primary cosmic ray interacts with the Martian atmosphere. We also compared the simulated results with the RAD measurements and found a reasonable agreement. Our results are important for future human exploration of Mars, for instance, to estimate the effectiveness of radiation shielding of a given geometry or for optimizing the radiation shielding design of a Martian habitat.〈/p〉
    Description: Plain Language Summary: Space agencies and private companies are working to place humans on the surface of Mars. Astronauts would be exposed to a different and considerably harsher radiation environment on Mars than humans are on Earth. Space radiation is largely determined by galactic cosmic rays, which have sufficient energy to reach the Martian surface. Thus, a better understanding of the radiation on the surface of Mars is needed. The shielding provided by the atmosphere increases with the zenith angle, and it also causes an increase in the creation of secondary particles. To better understand this, we perform a Geant4 Monte Carlo simulation to derive the dependence of the surface dose rate on the zenith angle 〈italic〉θ〈/italic〉. The results show that the radiation dose on the surface of Mars depends on the incoming angle of the primary radiation. Moreover, the radiation dose rate is significantly modulated by solar activity, and the Mars surface dose rate differs by about 50% between solar maximum and minimum periods. We validate our simulation by comparing the dose measured by the Mars Science Laboratory Radiation Assessment Detector and find good agreement.〈/p〉
    Description: Key Points: We model the downward radiation dose on the surface of Mars and find that it only depends weakly on the zenith angle. The surface dose rate depends on solar modulation, and weaker modulation results in higher dose rate for each.The local topographical features influence the Martian surface radiation.
    Description: Deutsches Zentrum für Luft‐und Raumfahrt http://dx.doi.org/10.13039/501100002946
    Description: Jet Propulsion Laboratory http://dx.doi.org/10.13039/100006196
    Description: Strategic Priority Program of CAS
    Description: National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809
    Description: Civil Aerospace Technologies
    Description: NASA Johnson Space Center
    Description: https://doi.org/10.17189/1519761
    Description: https://doi.org/10.17189/1519760
    Description: https://doi.org/10.17189/1523028
    Description: https://doi.org/10.5281/zenodo.7257306
    Keywords: ddc:523 ; space radiation ; Mars exploration ; MSL mission ; zenith angle
    Language: English
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  • 20
    Publication Date: 2023-07-27
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉In this paper we describe a method to compute spatial scales for images acquired by NASA's Mars Curiosity rover (Mars Science Laboratory, MSL). The method is based on the assumption that the rover stands on an infinite plane that may have any orientation with respect to the local gravity vector. While not new, it is the first time that this method is systematically applied to Martian images acquired by a lander. A continuously run software pipeline processes the images acquired by the rover within a 20 m radius, adds approximate scalebars to the raw images, and generates, whenever possible, rectified (warped) versions of those images. The products of this software pipeline and the chemical compositions of relevant rover science targets from NASA's Planetary Data System archive, are made available to the public via the Approximate Scale for Images and Chemistry website, which has been developed in collaboration with the Planetary Data System Analyst's Notebook for the MSL mission. Hyperlinks connect the two resources.〈/p〉
    Description: Plain Language Summary: We developed a software pipeline that calculates the spatial scale of images acquired by NASA's Mars Curiosity rover. The software pipeline is linked to a new website: the Approximate Scale for Images and Chemistry, in which the scalebar products are paired with information about the shape, size, color, and chemical composition of the imaged site, obtained by the rover suite of instruments. The images mimic the vantage point of human eyes and are therefore well‐suited to inspire field geologists (including those mainly working on Earth) to interpret Martian geologic features.〈/p〉
    Description: Key Points: A systematic method to generate approximate scalebars for obliquely acquired Martian landscape images was developed. A newly created Approximate Scale for Images and Chemistry (ASIC) website links images, color, spatial scale, and chemistry, as returned by NASA's Curiosity rover in Gale crater. The ASIC website is complementary and strongly linked to the Analyst's Notebook, the data resource for Martian/lunar landed missions.
    Description: Deutsche Forschungsgemeinschaft
    Description: Project DEAL
    Description: https://asic.mps.mpg.de/
    Description: https://an.rsl.wustl.edu/msl/
    Description: http://pds-geosciences.wustl.edu/msl/msl-m-chemcam-libs-4_5-rdr-v1/mslccm_1xxx/data/moc/
    Description: http://pds-geosciences.wustl.edu/msl/msl-m-chemcam-libs-4_5-rdr-v1/mslccm_1xxx/extras/rmi_mosaics/
    Description: http://pds-geosciences.wustl.edu/msl/msl-m-chemcam-libs-4_5-rdr-v1/mslccm_1xxx/extras/rmi_contours_in_mcam_images/
    Description: http://pds-geosciences.wustl.edu/msl/msl-m-apxs-4_5-rdr-v1/mslapx_1xxx/extras/
    Keywords: ddc:523 ; Mars ; Curiosity rover ; images ; spatial scale ; science targets ; chemistry
    Language: English
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  • 21
    Publication Date: 2023-07-21
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Parameterised by the Love number 〈italic〉k〈/italic〉〈sub〉2〈/sub〉 and the tidal quality factor 〈italic〉Q〈/italic〉, and inferred from lunar laser ranging (LLR), tidal dissipation in the Moon follows an unexpected frequency dependence often interpreted as evidence for a highly dissipative, melt‐bearing layer encompassing the core‐mantle boundary. Within this, more or less standard interpretation, the basal layer's viscosity is required to be of order 10〈sup〉15〈/sup〉–10〈sup〉16〈/sup〉 Pa s and its outer radius is predicted to extend to the zone of deep moonquakes. While the reconciliation of those predictions with the mechanical properties of rocks might be challenging, alternative lunar interior models without the basal layer are said to be unable to fit the frequency dependence of tidal 〈italic〉Q〈/italic〉. The purpose of our paper is to illustrate under what conditions the frequency‐dependence of lunar tidal 〈italic〉Q〈/italic〉 can be interpreted without the need for deep‐seated partial melt. Devising a simplified lunar model, in which the mantle is described by the Sundberg‐Cooper rheology, we predict the relaxation strength and characteristic timescale of elastically accommodated grain boundary sliding in the mantle that would give rise to the desired frequency dependence. Along with developing this alternative model, we test the traditional model with a basal partial melt; and we show that the two models cannot be distinguished from each other by the available selenodetic measurements. Additional insight into the nature of lunar tidal dissipation can be gained either by measurements of higher‐degree Love numbers and quality factors or by farside lunar seismology.〈/p〉
    Description: Plain Language Summary: As the Moon raises ocean tides on the Earth, the Earth itself gives rise to periodic deformation of the Moon. Precise measurements of lunar shape and motion can reveal those deformations and even relate them to our natural satellite's interior structure. In this work, we discuss two interpretations of those measurements. According to the first one, the lunar interior is hot and a small part of it might have melted, forming a thick layer of weak material buried more than 1,000 km deep under the lunar surface. According to the second one, there is no such layer, and the measured deformation can be explained by the behavior of solid rocks at relatively low temperatures. We show that the two possibilities cannot be distinguished from each other by the existing data.〈/p〉
    Description: Key Points: A lunar mantle governed by the Andrade model fits selenodetic constraints only with a very weak frequency dependence of tidal dissipation. We seek the parameters of two more complex models that may explain the anomalous frequency dependence of tidal 〈italic〉Q〈/italic〉 measured by lunar laser ranging. Both a dissipative basal layer and elastically accommodated grain‐boundary sliding in the deep mantle can result in the same tidal response.
    Description: Czech Science Foundation
    Description: https://doi.org/10.5281/zenodo.7788121
    Keywords: ddc:523 ; Moon ; tidal dissipation ; interior structure
    Language: English
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  • 22
    Publication Date: 2023-07-21
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉A seismic swarm affected the 53.3°–54.3° Latitude North section of the Mid‐Atlantic Ridge from 26 September to 10 December 2022. We rely on regional, teleseismic and array data to relocate 61 hypocenters and derive 77 moment tensors. The 2022 swarm released a cumulative moment equivalent to Mw 6.3. Seismicity was shallow (7 ± 3 km depth). Most earthquakes are located along the ridge axis with typical, NS oriented normal faulting mechanisms, but a few among the largest and latest earthquakes have unusual thrust mechanisms and locations as far as ∼25 km from the ridge. We attribute the swarm to a shallow magmatic intrusion, with a vertical dike first propagating ∼60 km along axis, accompanied by shallow normal faulting, and then thickening and triggering thrust earthquakes off the ridge, in response to compressive stress buildup. The unrest provides a rare example of an energetic, magmatic driven swarm episode at the mid‐ocean ridge.〈/p〉
    Description: Plain Language Summary: The largest plate boundary systems on Earth are Mid‐ocean ridges (MOR), where the plates continuously drift apart and new lithosphere is constantly being formed. Although the process is well understood, we rarely detect spreading events at MOR, mainly because these regions are remote and local monitoring is rarely possible. In September–November 2022 a large, unusual seismic swarm occurred along a spreading center ridge segment of the North Mid‐Atlantic Ridge. Despite the remoteness of the region, we managed to model regional and teleseismic data to perform earthquake relocation, depth estimation and moment tensor inversion. In this way, we could reconstruct the geometry and the evolution of the seismicity. We found that in the early days of the swarm, seismicity migrated unilaterally over ∼60 km along the ridge axis, from North to South, triggering normal faulting earthquakes, which are typical at MOR. Later, large thrust mechanisms, anomalous in an extensional environment, appeared and quickly became predominant. We explain seismological observations by a magmatic intrusion, which first propagated southward, producing shallow normal faulting earthquakes above the vertical magma dike, and later thickened, increasing compressional stresses on its sides, and triggering large thrust earthquakes.〈/p〉
    Description: Key Points: Analysis of a short, intense seismic swarm at the Mid‐Atlantic Ridge. Identification of unusual, thrust focal mechanisms in an extensional environment. Swarm triggered by dike intrusion at the mid‐ocean ridge.
    Description: German BMBF project EWRICA
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.5281/zenodo.8089070
    Keywords: ddc:551.22 ; seismic swarm ; Mid‐Atlantic Ridge ; seismicity ; magma dyke
    Language: English
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  • 23
    Publication Date: 2023-06-16
    Description: The angular momentum of the Earth‐Moon system was initially dominated by Earth's rotation with a short solar day of around 5 hr duration. Since then, Earth gradually transferred angular momentum through tidal friction to the orbit of the Moon, resulting in an increasing orbital radius and a deceleration of Earth's rotation. Geologic observations of tidal deposits can be used to verify and constrain models of lunar orbital evolution. In this work we reexamine the oldest tidal record suitable for analysis from the Moodies Group, South Africa, with an age of 3.22 billion years. Time frequency analysis of the series of thicknesses of the sandstone‐shale layers yields a periodicity of 15.0 layers, taking into account the possibility of missing laminae. Assuming a mixed tidal system, the duration of two neap‐spring‐neap cycles was 30.0 lunar days for dominant semidiurnal or 30.0 sidereal days for dominant diurnal tides. We derive the relationship between this observation and the past Earth‐Moon distance and re‐visit related published work. We find that the Earth‐Moon distance 3.2 billion years ago was about 70% of today's value. The Archean solar day was around 13 hr long. The ratio of solar to lunar tide‐raising torque controls the leakage of angular momentum from the Earth‐Moon system, but deviation from the assumed ratio of 0.211 results in only moderate changes. A duration of a postulated 21‐hr atmospheric resonance shorter than 200 million years would be consistent with our observation; it would significantly alter the Earth‐Moon distance.
    Description: Plain Language Summary: After its formation 4.5 billion years ago, the Moon circled Earth in a low orbit while Earth rotated faster than today around its axis. In the course of time, the Moon gradually evolved to a higher orbit while the rotation of Earth slowed due to the frictional effect of tides. Theoretical models can describe the evolution of the distance between Earth and the Moon with time until today. Counting the thickness of thin sandstone‐shale couplets of known age, which are layered due to tides, can constrain these models. In this work we reexamine the oldest of these geological records in the Moodies Group of South Africa, with an age of 3.2 billion years. The thickness of layers changes with a periodicity of 15 layers which is assumed to originate from varying strengths of currents between successive spring tides. Kepler's third law and the law of conservation of angular momentum allow us to derive the parameters of the lunar orbit from this measurement. According to our analysis, the Earth‐Moon distance was around 70% of today's value 3.2 billion years ago. The faster rotation rate of Earth resulted in a length of day of around 13 hr.
    Description: Key Points: Time frequency analysis yields 30.0 layers per two neap‐spring‐neap cycles, taking missing laminae in the tidal record into account. Earth‐Moon distance of ca. 70% of today's value 3.2 billion years ago results in a solar day of 13 hr duration. Duration of 21‐hr atmospheric resonance for 〈200 million years is consistent with our observation, alters estimate of Earth‐Moon distance.
    Keywords: ddc:523 ; Earth‐Moon system ; lunar orbital evolution ; tidal friction ; Moodies Group ; tidal deposits ; time‐frequency analysis
    Language: English
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  • 24
    Publication Date: 2023-06-12
    Description: Soils and landscapes are bridges of space and time, as they simultaneously and authentically show essential aspects that were previously separated by time and space (such as cultural and activity-related aspects from past and present) to the trained observer - albeit only in excerpts. Therefore, this article presents a series of impact indicators for soil changes, starting with extreme (anthropogenic) interventions and ending with equally extreme ("natural") events. An essential difference to specifically planning-relevant or human ecological concepts, which, for example, specify land use/load categories, is that the following impact indicators perceive soils as a phenomenon in themselves and do not define them through attributed functions. Particular attention is focused on their changeability and vital development potential, as well as on their property as a sphere of penetration of living and material things, with emphasis on the noetic effect. The intervention or event spaces on the earth's surface can be differentiated quantitatively through the type, strength, and duration of the phenomena. The intensity of all processes can be described by amplitude (the strength of the interventions/events) and frequency (the repetition rate of the interventions/events) and can be specifically identified and quantified by, for example, material inputs or outputs per unit of time. For the first time, there would be a system for measuring the ecological quality of anthropogenic land use, which could serve as an "alert system for the external technological culture," and could help us become aware of our "inner" culture.
    Description: research
    Keywords: ddc:550 ; Boden ; Landschaft ; Bodendegeneration ; Deutschland ; Anthropogene Bodenveränderung
    Language: German
    Type: doc-type:article
    Format: 9
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  • 25
    Publication Date: 2023-06-19
    Description: Energetic particle acceleration and energization in planetary magnetotails are often associated with dipolarization fronts characterized by a rapid increase of the meridional component of the magnetic field. Despite many studies of dipolarization events in Earth's magnetotail, Jupiter’s magnetotail provides an almost ideal environment to study high‐energetic ion acceleration by dipolarization fronts because of its large spatial scales and plasma composition of heavy and light ions. In this study, we focus on the response of different high‐energetic ion intensities (H, He, S, and O) to prominent magnetic dipolarization fronts inside the Jovian magnetotail. We investigate if ion energization and acceleration are present in the observations around the identified dipolarization fronts. Therefore, we present a statistical study of 87 dipolarization front signatures, which are identified in the magnetometer data of the Juno spacecraft from July 2016 to July 2021. For the ion intensity analysis, we use the energetic particle observations from the Jupiter Energetic Particle Detector Instrument. Our statistical study reveals that less than half of the identified events are accompanied by an increase of the ion intensities, while most of the other events show no significant change in the ion intensity dynamics. In about 40% of the events located in the dawn sector a significant decrease of the energy spectral index is detected indicating ion acceleration by the dipolarization fronts.
    Description: Key Points: Eighty‐seven prominent dipolarization front signatures are observed in the MAG data during Juno's prime mission during 21:00–05:30 local time. Less than half of the identified events are accompanied by an increase of the ion intensities. In 40% of the events observed on the dawn side a significant decrease of the energy spectral index indicates ion acceleration by the fronts.
    Description: Volkswagen Foundation http://dx.doi.org/10.13039/501100001663
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.17189/1519711
    Description: https://doi.org/10.17189/1519713
    Keywords: ddc:523 ; Juno ; Jovian magnetotail ; energetic ions ; dipolarization fronts ; JEDI
    Language: English
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  • 26
    Publication Date: 2023-10-24
    Description: Small stress changes such as those from sea level fluctuations can be large enough to trigger earthquakes. If small and large earthquakes initiate similarly, high‐resolution catalogs with low detection thresholds are best suited to illuminate such processes. Below the Sea of Marmara section of the North Anatolian Fault, a segment of ≈ $\approx $150 km is late in its seismic cycle. We generated high‐resolution seismicity catalogs for a hydrothermal region in the eastern Sea of Marmara employing AI‐based and template matching techniques to investigate the link between sea level fluctuations and seismicity over 6 months. All high resolution catalogs show that local seismicity rates are larger during time periods shortly after local minima of sea level, when it is already rising. Local strainmeters indicate that seismicity is promoted when the ratio of differential to areal strain is the largest. The strain changes from sea level variations, on the order of 30–300 nstrain, are sufficient to promote seismicity.
    Description: Plain Language Summary: Quasi‐periodic phenomena are a natural probe to test how the Earth's responses to a certain stress perturbation. High‐resolution catalogs with low detection thresholds may provide a new opportunity to look for this type of earthquake triggering. A segment of 150 km below the Sea of Marmara section of the North Anatolian Fault is late in its seismic cycle. Here, we generated high‐resolution seismicity catalogs for 6 months covering a hydrothermal region south of Istanbul in the eastern Sea of Marmara including seismicity up to MW 4.5. For first time in this region, we document a strong effect of the Sea of Marmara water level changes on the local seismicity. Both high‐resolution catalogs show that local seismicity rates are significantly larger during time periods shortly after local minima on sea level, when the sea level is rising. The available local instrumentation provided an estimate of the strain changes that were sufficient to promote seismicity. If such small stress perturbations from sea level changes are enough to trigger seismicity, it may suggest that the region is very close to failure.
    Description: Key Points: We generated enhanced seismicity catalogs to investigate the potential link between sea level change and seismicity in a hydrothermal region. Higher seismicity rates from the entire and declustered catalogs are observed during time periods when sea level is rising. Strain estimates from local strainmeters show that seismicity was promoted during reduced normal and enhanced shear strain conditions.
    Description: Helmholtz Association http://dx.doi.org/10.13039/501100009318
    Description: Alexander von Humboldt‐Stiftung http://dx.doi.org/10.13039/100005156
    Description: National Science Foundation http://dx.doi.org/10.13039/100000001
    Description: National Aeronautics and Space Administration http://dx.doi.org/10.13039/100000104
    Description: VW momentum
    Description: https://tdvms.afad.gov.tr/
    Description: http://www.koeri.boun.edu.tr/sismo/2/earthquake-catalog/
    Description: https://www.unavco.org/data/strain-seismic/bsm-data/bsm-data.html
    Keywords: ddc:551.22 ; seismicity catalog ; sea level change ; hydrothermal region ; strain ; strainmeter ; solid Earth tides
    Language: English
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  • 27
    Publication Date: 2024-01-19
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Faults and fractures may emplace fresh material onto Europa's surface, originating from shallow reservoirs within the ice shell or directly from the subsurface ocean. Ménec Fossae is a region of particular interest as it displays the interaction of several geological features, including bands, double ridges, chaotic terrains, and fossae, within a relatively small area. These features might affect the emplacement of buried material and subsequent exposure of fresh volatiles, prime targets for the upcoming 〈italic〉JUICE〈/italic〉 and 〈italic〉Europa Clipper〈/italic〉 missions in order to assess Europa's astrobiological potential. Previous studies have already revealed that a deep central trough is present at Ménec Fossae, flanked by several subparallel minor troughs and by a few asymmetrical scarps with lobate planforms. The presence of such features has motivated this study, given its potential to provide clear indications on the tectonic regime involved. Through detailed geomorphological‐structural mapping using 〈italic〉Galileo〈/italic〉 Solid State Imager data and terrain analysis on Digital Terrain Models, we could develop a novel hypothesis on the formation mechanisms that might have been involved in the study area. We propose that Ménec Fossae has been shaped by transtensional (strike‐slip with an extensional component) tectonic activity, as indicated by the orientation and relationship of the tectonic features present. Likely, such transtensional tectonism occurred above or associated with shallow subsurface water, consistent with the overall morphology and topography of the study area and the presence of chaotic terrains and double ridges. These results strengthen the case for widely distributed shallow water reservoirs within Europa's ice shell.〈/p〉
    Description: Plain Language Summary: Tectonic cracks, which can originate from shallow water bodies within the icy crust or directly from the subsurface ocean, may emplace fresh material onto Europa's surface. This kind of material is a prime target for upcoming space missions to assess Europa's habitability. We investigated the area of Ménec Fossae, which is characterized by many different geological features and structures within a relatively small area and can therefore provide clues on the mechanisms that shaped it. Our analyses were based on imaging and new topographic data, we developed a new hypothesis involving a combination of different tectonic styles as the driving processes for the formation of this area. This kind of tectonic activity could be related to a liquid water pocket located at a shallow depth within Europa's icy crust, which might explain the concurrent presence of some particular geological features in the area. These findings strengthen the case for the wide distribution of shallow water pockets distributed within the icy crust, which could allow future space missions to more easily assess Europa's habitability.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Detailed geomorphological‐structural analysis of Ménec Fossae has been conducted, using imaging and newly processed topographic data〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Ménec Fossae has been shaped by transtensional tectonic activity, potentially related to the emplacement of a shallow water reservoir〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The hypothesis that shallow water reservoirs are widely distributed within Europa's ice shell is strengthened〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: HORIZON EUROPE European Research Council http://dx.doi.org/10.13039/100019180
    Description: https://doi.org/10.17189/1520425
    Description: https://doi.org/10.5066/P9VKKK7C
    Description: https://doi.org/10.35003/8CU23S
    Keywords: ddc:523 ; Europa ; tectonics ; strike‐slip ; digital terrain models ; shallow water bodies ; Europa Clipper
    Language: English
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  • 28
    Publication Date: 2024-01-19
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉We analyze envelopes of 233 and 22 〈italic〉M〈/italic〉〈sub〉L〈/sub〉0.0 to 〈italic〉M〈/italic〉〈sub〉L〈/sub〉1.8 earthquakes induced by two geothermal stimulations in the Helsinki, Finland, metropolitan area. We separate source spectra and site terms and determine intrinsic attenuation and the scattering strength of shear waves in the 3–200 Hz frequency range using radiative transfer based synthetic envelopes. Displacement spectra yield scaling relations with a general deviation from self‐similarity, with a stronger albeit more controversial signal from the weaker 2020 stimulation. The 2020 earthquakes also tend to have a smaller local magnitude compared to 2018 earthquakes with the same moment magnitude. We discuss these connections in the context of fluid effects on rupture speed or medium properties. Site terms demonstrate that the spectral amplification relative to two reference borehole sites is not neutral at the other sensors; largest variations are observed at surface stations at frequencies larger than 30 Hz. Intrinsic attenuation is exceptionally low with 〈mml:math id="jats-math-1" display="inline"〉〈mml:semantics〉〈mml:mrow〉〈mml:msubsup〉〈mml:mi〉Q〈/mml:mi〉〈mml:mi mathvariant="normal"〉i〈/mml:mi〉〈mml:mrow〉〈mml:mo〉−〈/mml:mo〉〈mml:mn〉1〈/mml:mn〉〈/mml:mrow〉〈/mml:msubsup〉〈/mml:mrow〉〈mml:annotation encoding="application/x-tex"〉 ${Q}_{\mathrm{i}}^{-1}$〈/mml:annotation〉〈/mml:semantics〉〈/mml:math〉 values down to 2.4 × 10〈sup〉−5〈/sup〉 at 20 Hz, which allows the observation of a diffuse reflection at the ∼50 km deep Moho. Scattering strength is in the range of globally observed data with 〈mml:math id="jats-math-2" display="inline"〉〈mml:semantics〉〈mml:mrow〉〈mml:msubsup〉〈mml:mi〉Q〈/mml:mi〉〈mml:mrow〉〈mml:mi mathvariant="normal"〉s〈/mml:mi〉〈mml:mi mathvariant="normal"〉c〈/mml:mi〉〈/mml:mrow〉〈mml:mrow〉〈mml:mo〉−〈/mml:mo〉〈mml:mn〉1〈/mml:mn〉〈/mml:mrow〉〈/mml:msubsup〉〈/mml:mrow〉〈mml:annotation encoding="application/x-tex"〉 ${Q}_{\mathrm{s}\mathrm{c}}^{-1}$〈/mml:annotation〉〈/mml:semantics〉〈/mml:math〉 between 10〈sup〉−3〈/sup〉 and 10〈sup〉−4〈/sup〉. The application of the employed Qopen analysis program to the 2020 data in a retrospective monitoring mode demonstrates its versatility as a seismicity processing tool. The diverse results have implications for scaling relations, hazard assessment and ground motion modeling, and imaging and monitoring using ballistic and scattered wavefields in the crystalline Fennoscandian Shield environment.〈/p〉
    Description: Plain Language Summary: We analyze seismograms from earthquakes that were induced during two geothermal stimulation experiments in the Helsinki, Finland, metropolitan area, in 2018 and 2020. We process long signals including later parts of the seismograms to solve the persistent problem of separating the effects of the earthquake source process, of the bedrock, and of the ground immediately below a seismic sensor on the observed data. The high data quality allows us to measure systematic differences in some fundamental earthquake source parameters between events induced during the two stimulations. We attribute this to the effect of the fluids that were pumped into the 6 km deep rock formations. These observations are important since natural earthquakes and earthquakes induced by such underground engineering activities are governed by the same physical mechanisms. We also find that the bedrock in southern Finland is characterized by some of the lowest seismic attenuation values that have so far been measured in different tectonic environments. Last, the so‐called site effects at the instrument locations show a diverse amplification pattern in a wide frequency range, which is important for the assessment of shaking scenarios in the area.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉We find lower stress drop values for events induced by the 2020 compared to the 2018 stimulation and a deviation from self‐similar scaling〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The observation of a diffuse reflection at the 50 km deep Moho highlights the low intrinsic attenuation in the Fennoscandian Shield〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Site effect terms between 3 and 200 Hz show diverse frequency and site dependent patterns with high‐frequency amplification〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Academy of Finland
    Description: Geophysical Instrument Pool Potsdam
    Description: Institute of Seismology
    Description: University of Helsinki
    Description: https://github.com/trichter/qopen_finland
    Description: https://doi.org/10.23729/39cfac4f-4d0d-4fb4-83dc-6f67e8ba8dce
    Description: https://doi.org/10.23729/cdfd937c-37d5-46b0-9c16-f6e0c10bc81f
    Description: https://doi.org/10.23729/6d15a5ea-7671-4bab-88a1-71f4ed962276
    Keywords: ddc:551.22 ; seismic attenuation ; wave scattering and diffraction ; induced earthquakes ; earthquake source observations ; site effects ; Fennoscandian Shield
    Language: English
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  • 29
    Publication Date: 2023-11-14
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Standard models of force balance along Jovian field lines predict the location of the Io Plasma Torus to be the centrifugal equator of Jupiter’s magnetosphere, that is, the position along the magnetic field lines farthest away from Jupiter’s rotational axis. In many models, the centrifugal equator is assumed to lay on a plane, calculated from a (shifted) dipole magnetic field, rather than on a warped surface which incorporates Jupiter’s higher magnetic field moments. In this work, we use Hubble Space Telescope observations of the Io Main Footprint to constrain density, scale height, and lateral position of the Io Plasma Torus. Therefore, we employ the leading angle of the footprints to calculate expected travel times of Alfvén waves and carry out an inversion of the observations. For the magnetic field, we use the JRM33 magnetic field model. The inversion results show peak densities between 〈italic〉ρ〈/italic〉〈sub〉0〈/sub〉 = 1,830 cm〈sup〉−3〈/sup〉 and 〈italic〉ρ〈/italic〉〈sub〉0〈/sub〉 = 2,032 cm〈sup〉−3〈/sup〉 and scale heights between 〈italic〉H〈/italic〉 = 0.92〈italic〉R〈/italic〉〈sub〉〈italic〉J〈/italic〉〈/sub〉 and 〈italic〉H〈/italic〉 = 0.97〈italic〉R〈/italic〉〈sub〉〈italic〉J〈/italic〉〈/sub〉 consistent with current literature values. Using a warped multipole centrifugal equator instead of a planar dipole increases the quality of the fit by about 25%. We additionally develop two tests to confirm that the multipole centrifugal equator from the JRM33 model fits explains the applied data set better than the dipole centrifugal equator. The quadropole moments alter Io’s relative position to the torus, which changes the plasma density around Io by up to Δ〈italic〉ρ〈/italic〉/〈italic〉ρ〈/italic〉 = 20%.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Based on the Io Footprint positions, we show quantitatively that the Io Plasma Torus is centered on the centrifugal equator of Jupiter’s multipole magnetic field〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Position of the Io Footprint can be used to constrain a density model of the Io Plasma Torus〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The displacement of the Io Plasma Torus due to higher magnetic field moments can change the plasma density at Io by up to 20%〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: HORIZON EUROPE European Research Council
    Description: International Space Science Institute (ISSI) in Bern, through ISSI International Team project 515
    Description: https://doi.org/10.5281/zenodo.8214702
    Keywords: ddc:523 ; Io Plasma Torus ; inversion ; Io Footprint ; Alfven wings ; magnetic field model
    Language: English
    Type: doc-type:article
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  • 30
    Publication Date: 2024-04-03
    Description: The main sources of the ambient seismic wavefield in the microseismic frequency band (peaking in the ∼0.04–0.5 Hz range) are earth's oceans, namely the wind‐driven surface gravity waves (SGW) that couple oscillations into the seafloor and the upper crust underneath. Cyclones (e.g., hurricanes, typhoons) and other atmospheric storms are efficient generators of high ocean waves that in turn generate distinct microseismic signatures. In this study, we perform a polarization (i.e., three‐component) beamforming analysis of microseismic (0.05–0.16 Hz) retrograde Rayleigh and Love waves during major Atlantic hurricanes using a virtual array of seismometers in Eastern Canada. Oceanic hindcasts and meteorological data are used for comparison. No continuous generation of microseism along the hurricane track is observed but rather an intermittent signal generation. Both seismic surface wave types show clear cyclone‐related microseismic signatures that are consistent with a colocated generation at near‐coastal or shallow regions, however the Love wavefield is comparatively less coherent. We identify two different kinds of intermittent signals: (a) azimuthally progressive signals that originate with a nearly constant spatial lag pointing toward the trail of the hurricanes and (b) azimuthally steady signals remaining nearly constant in direction of arrival even days after the hurricane significantly changed its azimuth. This high complexity highlights the need for further studies to unravel the interplay between site‐dependent geophysical parameters, SGW forcing at depth and microseismic wavefield radiation and propagation, as well as the potential use of cyclone microseisms as passive natural sources.
    Description: Plain Language Summary: Ocean waves are responsible for the generation of microseisms, faint ground vibrations with complex characteristics and which comprise a major portion of the background seismic noise of the earth. In this study, we implement an onshore seismic detection method to study microseisms generated by cyclones in the North Atlantic ocean (hurricanes), as these are known to be major generators of large ocean waves. We observed that cyclones only seem to generate detectable microseisms as they move over certain regions in the ocean, namely near coastal or shallow water regions. The direction of arrival of these microseisms is sometimes constant, at other times it shifts azimuth along with the hurricanes. Understanding the relationship between ocean waves and cyclone‐related microseisms is an important step for the potential use of these vibrations to study the earth, ocean and atmosphere.
    Description: Key Points: Primary and secondary microseismic Love and Rayleigh waves excited by Atlantic cyclones were detected via onshore polarization beamforming. We observed microseisms related to cyclones as they pass over the northwestern Atlantic margin off Newfoundland. Some microseisms have constant direction of arrival, others are azimuthally progressive and reflect the advance of the cyclone.
    Description: German Research Foundation
    Description: https://doi.org/10.7289/V5NK3BZP
    Description: https://www.fdsn.org/networks/detail/CN/
    Description: http://ds.iris.edu/wilber3/
    Description: ftp://ftp.ifremer.fr/ifremer/ww3/HINDCAST
    Keywords: ddc:551.22 ; ambient seismic noise ; ocean microseisms ; hurricanes ; ocean gravity waves ; array seismology ; marine geophysics
    Language: English
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  • 31
    Publication Date: 2024-02-12
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Chaos terrains are geologically young and extensively disrupted surface features of Europa, thought to be an expression of the subsurface ocean interacting with the surface. The most prominent examples of this terrain on Europa are Conamara Chaos, and Thera and Thrace Maculae, all prime targets for the upcoming JUICE and Europa Clipper missions to assess the astrobiological potential of Europa. Of the three features, Thrace Macula is currently the least studied and understood. It intersects both Agenor Linea to the north and Libya Linea to the south, two important regional‐scale bands whose interaction with Thrace is yet to be fully unraveled, especially in terms of their relative ages of emplacement and activity. Using Galileo Solid State Imager data and Digital Terrain Models, we conducted detailed structural mapping and terrain analysis to develop a novel hypothesis on the mechanisms involved in the study area. We find that Thrace Macula is bordered along most sides by preexisting strike‐slip faults that have constrained its emplacement and areal distribution. We determine a sequence of events in the area involving the formation of Agenor Linea, followed by that of Libya Linea first and Thrace Macula later, and ultimately by strike‐slip tectonic activity likely driven by Libya Linea, that displaced a portion of Thrace Macula. Therefore, Thrace's subsurface material, uprising along faults postdating its formation, represents the freshest possible that could be sampled by future spacecraft in this region, a major consideration for the upcoming Europa Clipper mission.〈/p〉
    Description: Plain Language Summary: Europa, an icy moon of Jupiter with a large subterranean water reservoir, has unique surface features known as chaos terrains, believed to result from interactions between its subsurface ocean and surface. Of these terrains, Conamara Chaos and Thera and Thrace Maculae are prime targets for upcoming missions to investigate the astrobiological potential of Europa. However, Thrace Macula, which is situated between Agenor Linea to the north and Libya Linea to the south (two large‐scale bands, linear geological features), remains poorly understood. In this study, we used detailed mapping of faults and lineaments, together with topographical analysis, to propose a new hypothesis for the formation and evolution of Thrace Macula. Our findings suggest that preexisting tectonic faults constrained its emplacement and distribution, while a sequence of events starting with the formation of Agenor Linea, followed by Libya Linea first and Thrace Macula later, culminated in strike‐slip tectonic activity likely driven by Libya Linea that displaced a portion of Thrace Macula. These results imply that future spacecraft could sample Thrace's subsurface material uplifting along faults postdating its formation, the freshest available in this region. This research sheds light on Europa's regional history and its astrobiological potential.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉We conducted structural analysis on Thrace Macula, a chaotic terrain on Europa, based on imaging and newly processed topographic data〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉We found that preexisting strike‐slip faults border Thrace Macula and have constrained its emplacement and areal distribution〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉We provide insights into the history of Thrace and identify it as a prime location for future missions to sample fresh subsurface material〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: HORIZON EUROPE European Research Council http://dx.doi.org/10.13039/100019180
    Description: https://doi.org/10.17189/1520425
    Description: https://doi.org/10.5066/P9VKKK7C
    Description: https://doi.org/10.17169/refubium-38694
    Keywords: ddc:523 ; Europa ; chaos ; Thrace Macula ; strike‐slip tectonics ; Digital Terrain Models ; Europa Clipper
    Language: English
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  • 32
    Publication Date: 2024-05-23
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The 6 February 2023, 〈italic〉M〈/italic〉〈sub〉〈italic〉w〈/italic〉〈/sub〉 7.8 Pazarcık earthquake in the Turkey‐Syria border region raises the question of whether such a large earthquake could have been foreseen, as well as what is the maximum possible magnitude (〈italic〉M〈/italic〉〈sub〉max〈/sub〉) of earthquakes on the East Anatolian Fault (EAF) system and on continental transform faults in general. To answer such questions, knowledge of past earthquakes and of their causative faults is necessary. Here, we integrate data from historical seismology, paleoseismology, archeoseismology, and remote sensing to identify the likely source faults of fourteen 〈italic〉M〈/italic〉〈sub〉〈italic〉w〈/italic〉〈/sub〉 ≥ 7 earthquakes between 1000 CE and the present in the region. We find that the 2023 Pazarcık earthquake could have been foreseen in terms of location (the EAF) and timing (an earthquake along this fault was if anything overdue), but not magnitude. We hypothesize that the maximum earthquake magnitude for the EAF is in fact 8.2, that is, a single end‐to‐end rupture of the entire fault, and that the 2023 Pazarcık earthquake did not reach 〈italic〉M〈/italic〉〈sub〉max〈/sub〉 by a fortuitous combination of circumstances. We conclude that such unusually large events are hard to model in terms of recurrence intervals, and that seismic hazard assessment along continental transforms cannot be done on individual fault systems but must include neighboring systems as well, because they are not kinematically independent at any time scale.〈/p〉
    Description: Plain Language Summary: On 6 February 2023, there was a magnitude 7.8 earthquake in the Turkey‐Syria border region. It surprised many people, including many Earth scientists, because of where it happened (on the East Anatolian fault [EAF]) and because of how large it was. People wondered whether it could have been foreseen, and how large an earthquake on this fault can really be. To figure this out, we looked at the history of earthquakes in the region in the last 1,000 years. We used information from historical seismology, paleoseismology, archeoseismology, and remote sensing to identify the faults that caused 14 earthquakes with magnitude 7 or greater in this region. We found that the location (EAF) and timing (it was due any time) of the 2023 earthquake were foreseeable, but not the magnitude. In fact, we believe that the maximum magnitude for the EAF is 8.2, and that the 2023 earthquake was below this maximum just by accident. It is hard to say how often such large events can happen, because many different things need to align. We also believe that it is necessary to look at neighboring fault systems when estimating seismic hazards, because they interact.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉We identified the source faults of 14 large earthquakes along the East Anatolian and northern Dead Sea fault systems〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Maximum magnitude for the East Anatolian Fault (EAF) zone is approximately 8.2〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Continental transforms may be described as having a collective memory〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: https://doi.org/10.5270/ESA-c5d3d65
    Description: https://doi.org/10.1029/2019EA000658
    Description: https://doi.org/10.5194/essd-14-4489-2022
    Description: https://doi.org/10.25577/EWT8-KY06
    Description: https://dx.doi.org/10.5285/df93e92a3adc46b9a5c4bd3a547cd242
    Description: https://doi.org/10.5066/P985I7U2
    Description: https://app.box.com/v/textureshading
    Keywords: ddc:551.22 ; East Anatolian fault ; Dead Sea fault ; seismic gap ; seismic hazards ; source fault ; maximum earthquake magnitude
    Language: English
    Type: doc-type:article
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  • 33
    Publication Date: 2024-05-23
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Craters on the lunar surface can provide valuable information about the timing and sequence of surface‐forming processes on the Moon. A commonly used method for age determination is the analysis of the crater size‐frequency distribution (CSFD) to which a production function (PF) is fitted that represents the size‐frequency distribution of the impactors. However, the commonly used PF of Neukum (1983) is valid for crater diameters between 10 m and 300 km. Neukum et al. (2001, 〈ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1007/978-94-017-1035-0_3"〉https://doi.org/10.1007/978-94-017-1035-0_3〈/ext-link〉) revised the PF for crater diameters of 100 m–200 km. However, it is suggested to also be valid for the diameter range of 10 m–300 km as well. To assess whether we can extend a PF to craters ≤10 m in diameter, we investigated the slopes of the CSFDs of small craters formed on ejecta of young Copernican‐aged craters Giordano Bruno, Moore F, North Ray, and South Ray. A PF for smaller diameters would allow dating of young geological units, which are typically small, and would reduce the statistical error in age determinations, since smaller craters are more abundant. However, small craters are strongly influenced by geological factors, such as target properties, crater degradation, and secondary craters. For craters between 10 and 20 m we obtain a steeper CSFD slope than Neukum's proposed −3 slope (cumulative), whereas for craters ≤10 m the slope is about −3. We conclude that the PF of Neukum (1983) provides a reasonable CSFD slope for smaller craters, although it was not developed for this crater diameter range.〈/p〉
    Description: Plain Language Summary: Since the formation of the Moon, impactors have randomly hit the lunar surface. Older areas have larger and more abundant craters compared to younger areas. This relationship allows the determination of relative ages for different surfaces. A mathematical function can be fitted to the number and size of craters. This function has a specific shape and can be used to date a surface. Frequently used functions are valid between crater diameters of 10 m and 300 km. Dating young geological units is only possible if the observed craters are 〈bold〉≥〈/bold〉10 m in diameter. Therefore, an extension of these functions to crater diameters ≤10 m would be beneficial. However, small craters are strongly influenced by geological factors, such as target properties, crater degradation, and secondary craters. We consider these influences in our investigation. To compare our results with previous findings, we look more closely at the slope of the function that results from the number and size of the craters. Generally, we find that one function fits well for craters ≤10 m, even though it was not designed for this diameter range. This allows a more robust age determination because small craters are more abundant, reducing the statistical error.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉We studied small craters on young ejecta blankets to evaluate if the lunar production function (PF) is viable for craters ≤10 m〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The crater size‐frequency distributions (CSFDs) indicate that the PF can indeed be extended to crater diameters ≤10 m〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Our observed slopes of CSFDs at the studied Copernican‐aged craters are consistent with previous findings〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Deutsches Zentrum für Luft‐ und Raumfahrt http://dx.doi.org/10.13039/501100002946
    Description: https://doi.org/10.35003/V9AFAZ
    Description: https://doi.org/10.17189/1520341
    Description: https://ode.rsl.wustl.edu/moon/
    Description: https://wms.lroc.asu.edu/lroc/rdr_product_select
    Description: https://astrogeology.usgs.gov/search/map/Moon/Clementine/UVVIS/Lunar_Clementine_UVVIS_Warp_ClrRatio_Global_200m
    Description: https://aaronclauset.github.io/powerlaws/
    Keywords: ddc:523 ; crater size‐frequency distribution ; production function ; slope ; small craters ; Moon
    Language: English
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  • 34
    Publication Date: 2023-11-27
    Description: On 12 August 2021, a 〉220 s lasting complex earthquake with M〈sub〉w〈/sub〉 〉 8.2 hit the South Sandwich Trench. Due to its remote location and short interevent times, reported earthquake parameters varied significantly between different international agencies. We studied the complex rupture by combining different seismic source characterization techniques sensitive to different frequency ranges based on teleseismic broadband recordings from 0.001 to 2 Hz, including point and finite fault inversions and the back‐projection of high‐frequency signals. We also determined moment tensor solutions for 88 aftershocks. The rupture initiated simultaneously with a rupture equivalent to a M〈sub〉w〈/sub〉 7.6 thrust earthquake in the deep part of the seismogenic zone in the central subduction interface and a shallow megathrust rupture, which propagated unilaterally to the south with a very slow rupture velocity of 1.2 km/s and varying strike following the curvature of the trench. The slow rupture covered nearly two‐thirds of the entire subduction zone length, and with M〈sub〉w〈/sub〉 8.2 released the bulk of the total moment of the whole earthquake. Tsunami modeling indicates the inferred shallow rupture can explain the tsunami records. The southern segment of the shallow rupture overlaps with another activation of the deeper part of the megathrust equivalent to M〈sub〉w〈/sub〉 7.6. The aftershock distribution confirms the extent and curvature of the rupture. Some mechanisms are consistent with the mainshocks, but many indicate also activation of secondary faults. Rupture velocities and radiated frequencies varied strongly between different stages of the rupture, which might explain the variability of published source parameters.
    Description: Plain Language Summary: The earthquake of 12 August 2021 along the deep‐sea trench of the South Sandwich Islands in the South Atlantic reached a magnitude of 8.2 and triggered a tsunami. The automatic earthquake parameter determination of different agencies showed very different results shortly after the earthquake and partially underestimated the tsunami potential of the earthquake. A possible reason was the complex rupture process and that the tsunami was generated by a long and shallow slow slip rupture sandwiched between more conventional fast slip subevents at its northern and southern ends. In addition, the fault surface, which extended over 450 km, was highly curved striking 150°–220°. We investigated the different components of the seismic wavefields in different frequency ranges and with different methods. The analysis shows how even complex earthquakes can be deciphered by combining analyzing methods. The comparison with aftershocks and the triggered tsunami waves confirms our model that explains the South Sandwich rupture by four subevents in the plate boundary along the curved deep‐sea trench. Here, the depth, rupture velocities, and slip on each segment of the rupture vary considerably. The method can also be applied to other megathrust earthquakes and help to further improve tsunami warnings in the future.
    Description: Key Points: A combination of multiple approaches, inversion setups, and frequency ranges deciphered the complex earthquake of 2021 South Sandwich. The rupture consisted of four subevents with the largest occurring as a shallow slow rupture parallel to the South Sandwich Trench. Forward modeling proves that the large, shallow thrust subevent caused the recorded tsunami.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Agencia Nacional de Investigación y Desarrollo http://dx.doi.org/10.13039/501100020884
    Description: https://ds.iris.edu/wilbert3/find_event
    Description: https://www.usgs.gov/natural-hazards/earthquake-hazards/lists-maps-and-statistics
    Description: http://www.ioc-sealevelmonitoring.org/
    Description: https://doi.org/10.7289/V5C8276M
    Description: https://www.gfz-potsdam.de/en/software/tsunami-wave-propagations-easywave
    Keywords: ddc:551.22 ; 2021 South Sandwich Earthquake ; seismic characteristics ; tsunamigenic characteristics
    Language: English
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  • 35
    Publication Date: 2024-01-12
    Description: We investigate the small‐scale magnetic field fluctuations and their associated turbulent nature in the Io flux tube (IFT) connected to Io's footprint tail (IFPT). Our study is based on the recent magnetic field measurements by the Juno spacecraft during the PJ12 Juno flyby. Here, we are interested in understanding what type of turbulence is consistent with the fluctuations in the quasi‐dispersionless frequency range of 0.2–800 Hz as observed by Sulaiman et al. (2020), https://doi.org/10.1029/2020GL088432. Knowledge of the turbulent fluctuations is important to constrain the acceleration mechanisms for ions and electrons in the IFT. In this work, we suggest that the observed temporal fluctuations in the spacecraft frame correspond to Doppler‐shifted spatial fluctuation structured perpendicular to the background magnetic field. This would imply an alternative reinterpretation of the spectral index of the observed magnetic power spectral density to be potentially the result of weak‐MHD and sub‐ion scale kinetic Alfvén wave turbulence in the low‐frequency regime. Our theoretical modelings show that turbulence can be driven both in the torus region and at high‐latitudes rendering results in agreement with the Juno measurements. Calculated turbulence heating rates are consistent with observed energy fluxes in the IFT and represent efficient drivers for particle acceleration. Moreover, a widening of the IFPT structure with respect to the IFT extent is consistent with propagating dispersive Alfvén waves modified by kinetic effects on their group velocities.
    Description: Key Points: Low‐frequency Juno observations in the Io flux tube (IFT) tail represent structures perpendicular to background magnetic field. Magnetic field fluctuations observed in the Io footprint tail (IFPT) are consistent with weak‐MHD and sub‐ion kinetic Alfvén wave turbulence. Dispersion effects on group velocity of Alfvén waves widens the IFT consistent with the observed width of the IFPT.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.17189/1519711
    Description: https://doi.org/10.17189/1522461
    Keywords: ddc:523 ; Io ; Juno observations ; Alfvén waves ; magnetic field fluctuations
    Language: English
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  • 36
    Publication Date: 2023-01-14
    Description: The seasonal deposition and sublimation of CO2 constitute a major element in Martian volatile cycles. We reprocess the Mars Orbiter Laser Altimeter (MOLA) data and apply co‐registration procedures to obtain spatio‐temporal variations in levels of the Seasonal North Polar Cap (SNPC). The maximum level over the Residual North Polar Cap (RNPC) is 1.3 m, approximately half of that at the south pole (2.5 m). However, the maximum level in the dune fields at Olympia Undae can be up to 3.8 m. Furthermore, off‐season decreases up to 3 m during the northern winter at Olympia Undae are observed. These are likely due to metamorphism effects accentuated by the reduced snowfall at this period. Meanwhile, off‐season increases of up to 2 m during the northern spring are noted, the cause of which remains to be explored. The volume of the SNPC peaks at the end of northern winter and is estimated to be approximately 9.6 × 1012 m3, which is 2% more than that of the Seasonal South Polar Cap. The bulk density of the SNPC can go through phased decreases in accordance with phased accumulation at northern high‐latitudes. These findings can put important constraints on the Martian volatile cycling models.
    Description: Plain Language Summary: Due to its axial tilt, seasons also exist on Mars. Up to one third of the atmosphere's CO2 is in annual exchange with the polar regions through seasonal deposition/sublimation processes. Here, we make use of previously proposed approaches of analyzing the Mars Orbiter Laser Altimeter profiles and obtain spatio‐temporal level variations of the Seasonal North Polar Cap (SNPC). Particularly, we bring attention to abnormal behavior of the SNPC in the dune fields at Olympia Undae. Maximum level there can be all the way up to 4 m which is much higher than a maximum of 1.5 m over the Residual North Polar Cap. Meanwhile, off‐season decreases during the northern winter with magnitudes up to 3 m and off‐season increases during the northern spring of magnitudes up to 2 m are observed. These could possibly be related to metamorphism of the seasonal deposits and phased snowfall. The maximum volume of the SNPC is constrained to be 9.6 × 1012 m3. The bulk density of the SNPC does not continuously increase as previously assumed but can go through phased decreases in accordance with phased snowfall at the north pole. These findings can put important constraints on the Martian climate models.
    Description: Key Points: Through co‐registration of laser altimetry profiles, spatio‐temporal level variations of the Seasonal North Polar Cap (SNPC) of Mars are obtained. Maximum level of the SNPC can be up to 3.8 m at Olympia Undae and up to 1.3 m over the Residual North Polar Cap. Northern winter decreases of up to 3 m and northern spring increases of up to 2 m are observed at Olympia Undae.
    Description: China Scholarship Council
    Description: Deutsche Forschungsgemeinschaft
    Description: Institut National des Sciences de l’Univers
    Description: Centre National de la Recherche Scientifique
    Description: Centre National d’Etudes Spatiales
    Description: https://doi.org/10.17632/x953mzxxvv.1
    Description: https://doi.org/10.17632/z59b9nd6s9.2
    Description: https://pds-geosciences.wustl.edu/missions/mgs/pedr.html
    Description: https://naif.jpl.nasa.gov/pub/naif/pds/data/mgs-m-spice-6-v1.0/mgsp_1000/data/
    Description: https://www.uahirise.org/hiwish/browse
    Keywords: ddc:523 ; Mars ; seasonal polar cap ; CO2 ice ; MOLA ; level variation ; pseudo cross‐over
    Language: English
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  • 37
    Publication Date: 2023-01-15
    Description: Key knowledge about planetary composition can be recovered from the study of thermal infrared spectral range datasets. This range has a huge diagnostic potential because it contains diagnostic absorptions from a planetary surface and atmosphere. The main goal of this study is to process and interpret the dataset from the Thermal Infrared channel (TIRVIM) which is part of the Atmospheric Chemistry Suite of the ExoMars2016 Trace Gas Orbiter mission to find and characterize dust and water ice clouds in the atmosphere. The method employed here is based on the application of principal component analysis and target transformation techniques to extract the independent variable components present in the analyzed dataset. Spectral shapes of both atmospheric dust and water ice aerosols have been recovered from the analysis of TIRVIM data. The comparison between our results with those previously obtained on Thermal Emission Spectrometer (TES) data and with previous analysis on TIRVIM data, validates the methodology here applied, showing that it allows to correctly recover the atmospheric spectral endmembers present in the TIRVIM data. Moreover, comparison with atmospheric retrievals on PFS, TES and IRIS data, allowed us to assess the temporal stability and homogeneity of dust and water ice components in the Martian atmosphere over a time period of almost 50 years.
    Description: Plain Language Summary: The analysis of thermal infrared datasets from planetary bodies is of key importance for the understanding of a planet's climate evolution and history: it contains valuable information about composition, temperature and state of the atmosphere. Moreover, surface properties and the surface‐atmosphere interaction can be studied. Here we investigated new thermal infrared data from the Thermal Infrared channel instrument of the ExoMars Trace Gas Orbiter with the main goal of carefully identifying Martian atmospheric dust and water ice clouds components. A methodology based on principal component and target transformation factor analysis techniques has been applied. Based on our results, this methodology can correctly recover both atmospheric dust and water ice aerosols spectral shapes and their abundances in the Martian atmosphere.
    Description: Key Points: First successful application of principal components and target transformation techniques to high‐resolution Thermal Infrared channel (TIRVIM) data. Spectral shapes of both atmospheric dust and water ice clouds are recognized and recovered. TIRVIM data are successfully modeled through a linear combination of the recovered water ice and dust end‐members.
    Description: Roscosmos and ESA
    Description: https://doi.org/10.5281/zenodo.7032738
    Keywords: ddc:523 ; Martian atmosphere ; TIRVIM data
    Language: English
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  • 38
    Publication Date: 2023-01-21
    Description: Seismicity models are probabilistic forecasts of earthquake rates to support seismic hazard assessment. Physics‐based models allow extrapolating previously unsampled parameter ranges and enable conclusions on underlying tectonic or human‐induced processes. The Coulomb Failure (CF) and the rate‐and‐state (RS) models are two widely used physics‐based seismicity models both assuming pre‐existing populations of faults responding to Coulomb stress changes. The CF model depends on the absolute Coulomb stress and assumes instantaneous triggering if stress exceeds a threshold, while the RS model only depends on stress changes. Both models can predict background earthquake rates and time‐dependent stress effects, but the RS model with its three independent parameters can additionally explain delayed aftershock triggering. This study introduces a modified CF model where the instantaneous triggering is replaced by a mean time‐to‐failure depending on the absolute stress value. For the specific choice of an exponential dependence on stress and a stationary initial seismicity rate, we show that the model leads to identical results as the RS model and reproduces the Omori‐Utsu relation for aftershock decays as well stress‐shadowing effects. Thus, both CF and RS models can be seen as special cases of the new model. However, the new stress response model can also account for subcritical initial stress conditions and alternative functions of the mean time‐to‐failure depending on the problem and fracture mode.
    Description: Plain Language Summary: One of the most pressing questions in earthquake physics is understanding where and when earthquakes occur and how seismicity is related to stress changes in the Earth's crust. This question is even more important today because humans are increasingly influencing stresses in the Earth by exploiting the subsurface. So far, two classes of physics‐based seismicity models have been used primarily. One assumes instantaneous earthquake occurrence when stress exceeds a threshold, and the other is based on the nucleation of earthquakes according to friction laws determined in the laboratory. Both models are very different in their approaches, have advantages and disadvantages, and are limited in their applicability. In this paper, we introduce a new concept of seismicity models, which is very simple and short to derive and combines the strengths of both previous models, as shown in various applications to human‐related seismicity. The forecasts of both traditional models turn out to be special cases of the new model.
    Description: Key Points: We introduce a modified Coulomb Failure seismicity model in which a mean time‐to‐failure replaces instantaneous triggering. The model explains the main features of time‐dependent seismicity, including aftershock activity and stress shadow effects. As a special case, it includes the rate‐state model solutions but can also handle subcritical stresses and other fracture types.
    Description: European Unions 2020 research and innovation programme
    Description: https://github.com/torstendahm/tdsr
    Keywords: ddc:551.22 ; seismicity ; physics based model ; earthquake physics
    Language: English
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  • 39
    Publication Date: 2023-01-21
    Description: An earthquake‐induced stress drop on a megathrust instigates different responses on the upper plate and slab. We mimic homogenous and heterogeneous megathrust interfaces at the laboratory scale to monitor the strain relaxation on two elastically bi‐material plates by establishing analog velocity weakening and neutral materials. A sequential elastic rebound follows the coseismic shear‐stress drop in our elastoplastic‐frictional models: a fast rebound of the upper plate and the delayed and smaller rebound on the elastic belt (model slab). A combination of the rebound of the slab and the rapid relaxation (i.e., elastic restoration) of the upper plate after an elastic overshooting may accelerate the relocking of the megathrust. This acceleration triggers/antedates the failure of a nearby asperity and enhances the early slip reversal in the rupture area. Hence, the trench‐normal landward displacement in the upper plate may reach a significant amount of the entire interseismic slip reversal and speeds up the stress build‐up on the upper plate backthrust that emerges self‐consistently at the downdip end of the seismogenic zones. Moreover, the backthrust switches its kinematic mode from a normal to reverse mechanism during the coseismic and postseismic stages, reflecting the sense of shear on the interface.
    Description: Plain Language Summary: Subduction zones, where one tectonic plate slides underneath the other, host the largest earthquakes on earth. Two plates with different physical properties define the upper and lower plates in the subduction zones. A frictional interaction at the interface between these plates prevents them from sliding and builds up elastic strain energy until the stress exceeds their strength and releases accumulated energy as an earthquake. The source of the earthquake is located offshore; hence illuminating the plates' reactions to the earthquakes is not as straightforward as the earthquakes that occur inland. Here we mimic the subduction zone at the scale of an analog model in the laboratory to generate analog earthquakes and carefully monitor our simplified model by employing a high‐resolution monitoring technique. We evaluate the models to examine the feedback relationship between upper and lower plates during and shortly after the earthquakes. We demonstrate that the plates respond differently and sequentially to the elastic strain release: a seaward‐landward motion of the upper plate and an acceleration in the lower plate sliding underneath the upper plate. Our results suggest that these responses may trigger another earthquake in the nearby region and speed up the stress build‐up on other faults.
    Description: Key Points: Seismotectonic scale models provide high‐resolution observations to study the surface deformation signals from shallow megathrust earthquakes. Surface displacement time‐series suggest a sequential elastic rebound of the upper plate and slab during great subduction megathrust earthquakes. Slip reversal may be caused by rapid restoration of the upper plate after overshooting and amplified upper plate motion.
    Description: SUBITOP Marie Sklodowska‐Curie Action project from the European Union's EU Framework Programme
    Description: Deutsche Forschungsgemeinschaft
    Description: https://doi.org/10.5880/fidgeo.2022.024
    Keywords: ddc:551.22 ; analog modeling ; megathrust earthquake ; seismic cycle ; elastic rebound ; upper plate ; overshooting
    Language: English
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  • 40
    Publication Date: 2023-01-12
    Description: Transient magnetic reconnection plays an important role in energetic particle acceleration in planetary magnetospheres. Jupiter's magnetosphere provides a unique natural laboratory to study processes of energy transport and transformation. Strong electric fields in spatially confined structures such as plasmoids can be responsible for ion acceleration to high energies. In this study we focus on the effectiveness of ion energization and acceleration in plasmoids. Therefore, we present a statistical study of plasmoid structures in the predawn magnetotail, which were identified in the magnetometer data of the Juno spacecraft from 2016 to 2018. We additionally use the energetic particle observations from the Jupiter Energetic Particle Detector Instrument which discriminates between different ion species. We are particularly interested in the analysis of the acceleration and energization of oxygen, sulfur, helium, and hydrogen ions. We investigate how the event properties, such as the radial distance and the local time of the observed plasmoids in the magnetotail, affect the ion intensities close to the current sheet center. Furthermore, we analyze if ion acceleration is influenced by magnetic field turbulence inside the plasmoids. We find significant heavy ion acceleration in plasmoids close to the current sheet center which is in line with the previous statistical results based on Galileo observations conducted by Kronberg et al. (2019, https://doi.org/10.1029/2019JA026553). The observed effectiveness of the acceleration is dependent on the position of Juno in the magnetotail during the plasmoid event observation. Our results show no correlation between magnetic field turbulence and nonadiabatic acceleration for heavy ions during plasmoids.
    Description: Key Points: Intensity of heavy ions is strongly increased during plasmoids close to the current sheet center. Significant increase of heavy ion intensities is observed in plasmoids with larger wave power. Acceleration of heavy and light ions in plasmoids due to resonant interaction with the magnetic field fluctuations could not be observed.
    Description: Volkswagen Foundation (VolkswagenStiftung) http://dx.doi.org/10.13039/501100001663
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: NASA
    Description: https://pds-ppi.igpp.ucla.edu/
    Keywords: ddc:523 ; plasmoids ; Juno ; JEDI ; ion acceleration
    Language: English
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  • 41
    Publication Date: 2023-01-13
    Description: Recent observations by the Juno spacecraft have shown that electrons contributing to Jupiter's main auroral emission appear to be frequently characterized by broadband electron distributions, but also less often mono‐energetic electron distributions are observed as well. In this work, we quantitatively derive the occurrence rates of the various electron distributions contributing to Jupiter's aurora. We perform a statistical analysis of electrons measured by the JEDI‐instrument within 30–1,200 keV from Juno's first 20 orbits. We determine the electron distributions, either pancake, field‐aligned, mono‐energetic, or broadband, through energy and pitch angles to associate various acceleration mechanisms. The statistical analysis shows that field‐aligned accelerated electrons at magnetic latitudes greater than 76° are observed in 87.6% ± 7.2% of the intervals time averaged over the dipole L‐shells according the main oval. Pancake distributions, indicating diffuse aurora, are prominent at smaller magnetic latitudes (〈76°) with an occurrence rate of 86.2% ± 9.6%. Within the field‐aligned electron distributions, we see broadband distributions 93.0% ± 3.8% of the time and a small fraction of isolated mono‐energetic distribution structures 7.0% ± 3.8% of the time. Furthermore, these occurrence statistics coincide with the findings from our energy flux statistics regarding the electron distributions. Occurrence rates thus also characterize the overall energetics of the different distribution types. This study indicates that stochastic acceleration is dominating the auroral processes in contrast to Earth where the discrete aurora is dominating.
    Description: Plain Language Summary: With the Juno spacecraft arriving in the magnetosphere of Jupiter, first flyby particle measurements have changed the knowledge about the developing process of Jupiter's intense aurora. The observations of auroral particles show a stochastic behavior rather than a preference for specific energy. Our statistical analysis of the first 20 flybys at Jupiter compares the occurrence of different particle distributions and highlights the importance of different generation theories for Jupiter's aurora. A generation via stochastic rather than mono‐energetic behavior is deduced and supports previous observations.
    Description: Key Points: We present a statistical study of Jupiter's auroral electrons within 30–1,200 keV based on Juno's first 20 perijoves. Broadband electron distributions dominates Jupiter's main auroral zone as they are observed in 93% ± 3% of the intervals studied here. Dominance of broadband distributions underlines the importance of a turbulent or stochastic acceleration process.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Universität zu Köln http://dx.doi.org/10.13039/501100008001
    Description: https://lasp.colorado.edu/home/mop/files/2015/02/CoOrd_systems7.pdf
    Description: https://pds-ppi.igpp.ucla.edu/mission/JUNO/JNO/JEDI
    Description: https://lasp.colorado.edu/home/mop/files/2020/04/20190412_Imai_MagFootReader_UIowa_rev.pdf
    Keywords: ddc:523 ; auroral precipitation budget ; particle distribution ; Jupiter ; Juno
    Language: English
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  • 42
    Publication Date: 2023-01-19
    Description: Along ultraslow spreading ridges melt is distributed unequally, but melt focusing guides melt away from amagmatic segments toward volcanic centers. An interplay of tectonism and magmatism is thought to control melt ascent, but the detailed process of melt extraction is not yet understood. We present a detailed image of the seismic velocity structure of the Logachev volcanic center and adjacent region along the Knipovich Ridge. With travel times of P‐ and S‐waves of 3,959 earthquakes we performed a local earthquake tomography. We simultaneously inverted for source locations, velocity structure and the Vp/Vs‐ratio. An extensive low velocity anomaly coincident with high Vp/Vs‐ratios 〉1.9 lies underneath the volcanic center at depths of 10 km below sea level in an aseismic area. More shallow, tightly clustered earthquake swarms connect the anomaly to a shallow anomaly with high Vp/Vs‐ratio beneath the basaltic seafloor. We consider the deep low‐velocity anomaly to represent an area of partial melt from which melts ascent vertically to the surface and northwards into the adjacent segment. By comparing tomographic studies of the Logachev and Southwest Indian Ridge Segment‐8 volcano we conclude that volcanic centers of ultraslow spreading ridges host spatially confined, circular partial melt areas below 10 km depth, in contrast to the shallow extended melt lenses along fast spreading ridges. Lateral feeding over distances of 35 km is possible at orthogonal spreading segments, but limited at the obliquely spreading Knipovich Ridge.
    Description: Plain Language Summary: Mid‐ocean ridges mark the tectonic plate boundaries, where the plates drift apart. Fresh magma rises into the gap and builds new seafloor. The slower the plates drift apart, the less magma is present underneath the ridge. At very slow spreading ridges there is not enough magma to build new seafloor along the entire length of the ridge. Rather, melt is guided toward individual volcanic centers spaced at about 100 km, where melt accumulates and ascents. In our study we try to find melt storage areas and ascent paths of such a volcanic center. With velocities of different seismic wave types from earthquakes we map the velocity structure of the area underneath the major Logachev volcanic center. Lower velocities indicate an area partly including melt at depths of more than 10 km, far deeper than at mid‐ocean ridges with sufficient melt supply. From the deep magma reservoir, many earthquake swarms map the long ascent path of melt to the surface. The interplay of magmatic and tectonic activity is important here. In a comparison with results from another volcanic center, we find that lateral magma feeding is possible in orthogonal spreading, but limited in oblique spreading, as at the Knipovich Ridge.
    Description: Key Points: Active volcanic centers at ultraslow spreading ridges host deeper and more confined partial melt areas than faster spreading ridges. Earthquake swarms delineate melt ascent paths from the partial melt area to the surface. Lateral feeding at shallow depths into subordinate segments is prevented by ridge obliquity.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.22 ; ultraslow spreading ; Knipovich Ridge ; local earthquake tomography ; seismicity ; mid‐ocean ridge ; partial melt area
    Language: English
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  • 43
    Publication Date: 2023-01-20
    Description: We constrain Europa's tenuous atmosphere on the subsolar hemisphere by combining two sets of observations: oxygen emissions at 1,304 and 1,356 Å from Hubble Space Telescope (HST) spectral images and Galileo magnetic field measurements from its closest encounter, the E12 flyby. We describe Europa's atmosphere with three neutral gas species: global molecular (O2) and atomic oxygen (O), and localized water (H2O) present as a near‐equatorial plume and as a stable distribution concentrated around the subsolar point on the moon's trailing hemisphere. Our combined modeling based on the ratio of OI 1,356 to OI 1,304 Å emissions from Roth (2021; https://doi.org/10.1029/2021gl094289) and on magnetic field data allows us to derive constraints on the density and location of O2 and H2O in Europa's atmosphere. We demonstrate that 50% of the O2 and between 50% and 75% of the H2O abundances from Roth (2021; https://doi.org/10.1029/2021gl094289) are required to jointly explain the HST and Galileo measurements. These values are conditioned on a column density of O close to the upper limit of 6 × 1016 m−2 derived by Roth (2021; https://doi.org/10.1029/2021gl094289), and on a strongly confined stable H2O atmosphere around the subsolar point. Our analysis yields column densities of 1.2 × 1018 m−2 for O2, and 1.5 × 1019 to 2.2 × 1019 m−2 at the subsolar point for H2O. Both column densities, however, still lie within the uncertainties of Roth (2021; https://doi.org/10.1029/2021gl094289). Our results provide additional evidence for the existence of a stable H2O atmosphere at Europa.
    Description: Key Points: We combine Hubble Space Telescope spectral images and Galileo magnetometer data to constrain the density and location of water vapor in Europa's atmosphere. We simulate the plasma interaction for the Galileo E12 flyby with a three‐component atmosphere: global O2, stable confined H2O, and a plume. Using 50% of O2 and from 50% to 75% of H2O column densities from Roth (2021) yields magnetic field signatures consistent with both observations.
    Description: European Research Council http://dx.doi.org/10.13039/100010663
    Description: http://doi.org/10.17189/1519667
    Keywords: ddc:523 ; Europa ; Jupiter ; moon‐magnetosphere interaction ; icy moons ; atmosphere
    Language: English
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  • 44
    Publication Date: 2024-01-15
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉On 7 June 2021 the Juno spacecraft visited Ganymede and provided the first in situ observations since Galileo's last flyby in 2000. The measurements obtained along a one‐dimensional trajectory can be brought into global context with the help of three‐dimensional magnetospheric models. Here we apply the magnetohydrodynamic model of Duling et al. (2014, 〈ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1002/2013ja019554"〉https://doi.org/10.1002/2013ja019554〈/ext-link〉) to conditions during the Juno flyby. In addition to the global distribution of plasma variables we provide mapping of Juno's position along magnetic field lines, Juno's distance from closed field lines and detailed information about the magnetic field's topology. We find that Juno did not enter the closed field line region and that the boundary between open and closed field lines on the surface matches the poleward edges of the observed auroral ovals. To estimate the sensitivity of the model results, we carry out a parameter study with different upstream plasma conditions and other model parameters.〈/p〉
    Description: Plain Language Summary: In June 2021 the Juno spacecraft flew close to Ganymede, the largest moon of Jupiter, and explored its magnetic and plasma environment. Ganymede's own magnetic field forms a magnetosphere, which is embedded in Jupiter's large‐scale magnetosphere, and which is unique in the solar system. The vicinity of Ganymede is separated into regions that differ in whether the magnetic field lines connect to Ganymede's surface at both or one end or not at all. These regions are deformed by the plasma flow and determine the state of the plasma and the location of Ganymede's aurora. We perform simulations of the plasma flow and interaction to reveal the three‐dimensional structure of Ganymede's magnetosphere during the flyby of Juno. The model provides the three‐dimensional state of the plasma and magnetic field, predicted locations of the aurora and the geometrical magnetic context for Juno's trajectory. These results are helpful for the interpretation of the in situ and remote sensing obtained during the flyby. We find that Juno did not cross the region with field lines that connect to Ganymede's surface at both ends. Considering possible values for unknown model parameters, we also estimate the uncertainty of the model results.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Our magnetohydrodynamic model illustrates the state of Ganymede's magnetosphere during Juno's flyby and locates its trajectory outside closed field lines〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The location of the open‐closed‐field line‐boundary is predicted and matches the poleward edges of the aurora as observed by Juno〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉We investigate model uncertainties caused by incomplete knowledge of upstream conditions and other parameters〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: H2020 European Research Council http://dx.doi.org/10.13039/100010663
    Description: University of Iowa http://dx.doi.org/10.13039/100008893
    Description: National Aeronautics and Space Administration http://dx.doi.org/10.13039/100000104
    Description: Southwest Research Institute http://dx.doi.org/10.13039/100011766
    Description: http://www.netpurgatory.com/zeusmp.html
    Description: https://doi.org/10.17189/1519711
    Description: https://doi.org/10.5281/zenodo.7096938
    Description: https://doi.org/10.5281/zenodo.7105334
    Keywords: ddc:523 ; Ganymede ; Juno spacecraft ; MHD model ; magnetosphere ; magnetohydrodynamics ; simulation
    Language: English
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  • 45
    Publication Date: 2023-11-14
    Description: We report results of Hubble Space Telescope observations from Ganymede's orbitally trailing side which were taken around the flyby of the Juno spacecraft on 7 June 2021. We find that Ganymede's northern and southern auroral ovals alternate in brightness such that the oval facing Jupiter's magnetospheric plasma sheet is brighter than the other one. This suggests that the generator that powers Ganymede's aurora is the momentum of the Jovian plasma sheet north and south of Ganymede's magnetosphere. Magnetic coupling of Ganymede to the plasma sheet above and below the moon causes asymmetric magnetic stresses and electromagnetic energy fluxes ultimately powering the auroral acceleration process. No clear statistically significant timevariability of the auroral emission on short time scales of 100s could be resolved. We show that electron energy fluxes of several tens of mW m−2 are required for its OI 1,356 Å emission making Ganymede a very poor auroral emitter.
    Description: Plain Language Summary: Jupiter's moon Ganymede is the largest moon in the solar system and the only known moon with an intrinsic magnetic field and two auroral ovals around its north and south poles. Earth also possesses two auroral ovals, which are bands of emission around its poles. This emission is also referred to as northern and southern lights. We use the Hubble Space Telescope to observe Ganymede's aurora around the time when NASA's Juno spacecraft had a close flyby at Ganymede. We find that the brightness of the northern and southern ovals alternate in intensity with a period of 10 hr. Additionally, we derive that an energy flux of several tens of milli‐Watt per square meter is necessary to power the auroral emission. This energy flux comes from energetic electrons accelerated in the vicinity of Ganymede.
    Description: Key Points: Hubble Space Telescope observations of Ganymede's orbitally trailing hemisphere on 7 June 2021 in support of Juno flyby. Brightness ratio of northern and southern auroral ovals oscillates such that the oval facing the Jovian plasma sheet is brighter. Oscillation suggests the aurora is driven by magnetic stresses coupling the moon's magnetic field to the surrounding Jovian plasma sheet.
    Description: European Research Council, ERC
    Description: NASA
    Description: http://archive.stsci.edu/hst/
    Keywords: ddc:523 ; Ganymede ; auroral ovals ; Hubble Space Telescope ; Juno spacecraft
    Language: English
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  • 46
    Publication Date: 2024-03-25
    Description: We use interferometric synthetic aperture radar observations to investigate the fault geometry and afterslip evolution within 3 years after a mainshock. The postseismic observations favor a ramp‐flat structure in which the flat angle should be lower than 10°. The postseismic deformation is dominated by afterslip, while the viscoelastic response is negligible. A multisegment, stress‐driven afterslip model (hereafter called the SA‐2 model) with depth‐varying frictional properties better explains the spatiotemporal evolution of the postseismic deformation than a two‐segment, stress‐driven afterslip model (hereafter called the SA‐1 model). Although the SA‐2 model does not improve the misfit significantly, this multisegment fault with depth‐varying friction is more physically plausible given the depth‐varying mechanical stratigraphy in the region. Compared to the kinematic afterslip model, the mechanical afterslip models with friction variation tend to underestimate early postseismic deformation to the west, which may indicate more complex fault friction than we expected. Both the kinematic and stress‐driven models can resolve downdip afterslip, although it could be affected by data noise and model resolution. The transition depth of the sedimentary cover basement interface inferred by afterslip models is ∼12 km in the seismogenic zone, which coincides with the regional stratigraphic profile. Because the coseismic rupture propagated along a basement‐involved fault while the postseismic slip may activate the frontal structures and/or shallower detachments in the sedimentary cover, the 2017 Sarpol‐e Zahab earthquake may have acted as a typical event that contributed to both thick‐ and thin‐skinned shortening of the Zagros in both seismic and aseismic ways.
    Description: Plain Language Summary: The 2017 Mw 7.3 Sarpol‐e Zahab earthquake is the largest instrumentally recorded event to have ruptured in the Zagros fold thrust belt. Although much work has been conducted for a better understanding of the relationship between crustal shortening and seismic and aseismic slip of the earthquakes in the Zagros, active debate remains. Here, we use interferometric synthetic aperture radar observations to study the fault geometry and afterslip evolution within 3 years after the 2017 Mw 7.3 Sarpol‐e Zahab earthquake. For postseismic deformation sources, afterslip and viscoelastic relaxation are considered to be possible causes of postseismic deformation. Our results show that the kinematic afterslip model can spatiotemporally explain the postseismic deformation. However, the mechanical afterslip models tend to underestimate the earlier western part of the postseismic deformation, which may indicate a more complex spatial heterogeneity of the frictional property of the fault plane. We find that there is deep afterslip downdip of coseismic slip from both the kinematic and stress‐driven afterslip models, although it could be affected by data noise and model resolution. We additionally find that the viscoelastic response is negligible. Postseismic slip on more complex geological structures may also be reactivated and triggered, combined with geodetic inversions, geological cross‐section data and local structures in the Zagros.
    Description: Key Points: The Spatiotemporal evolution of postseismic observations favors a ramp‐flat structure in which the flat angle should be lower than 10°, Depth‐varying friction is required to better simulate the rate‐strengthening afterslip evolution. Downdip afterslip can be resolved by afterslip models, although it relies on data accuracy and model resolution.
    Description: National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809
    Description: China Scholarship Council http://dx.doi.org/10.13039/501100004543
    Description: Ministry of Science and Technology in Taiwan
    Description: https://www.asf.alaska.edu/
    Description: http://irsc.ut.ac.ir/
    Description: https://www.globalcmt.org/
    Description: https://doi.org/10.5281/zenodo.7113073
    Keywords: ddc:551.22 ; Zagros fold thrust belt ; Sarpol-e Zahab earthquake ; postseismic observations ; postseismic deformation ; InSAR
    Language: English
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  • 47
    Publication Date: 2024-02-21
    Description: Subsurface oceans rich in salts may be prevalent in the icy worlds of the outer solar system. Surface observations have led to various hypotheses for the transport of materials from the seafloor to the surface by hydrothermal plumes, and raise questions about heat transfer mechanisms. Chemical heterogeneity affects the vigor of convection, the forms of plumes, the generation and destruction of stratified or finger structures in the ocean, and thus the transport of heat and materials from the interior to the surface. Here, we investigate the layering phenomenon in a double‐diffusive convection system, which can occur when both the temperature and concentration influence the density of the fluid. The persistence of layers may depend on the buoyancy ratio, the Rayleigh number, boundary conditions, and initial conditions, which alter the chemical distribution and thus the balance between thermal and chemical buoyancies. Our simulations suggest that the layering could exist for a longer duration if the buoyancy ratio is raised with boundary conditions that maintain a large concentration difference. When the layers are present, heat and material transport are significantly inhibited through the subsurface ocean from the silicate interior to the base of the icy shell.
    Description: Plain Language Summary: The subsurface oceans of icy satellites are almost certainly salt to some degree, and this gives rise to the possibility of layering by the process of double‐diffusive convection. The evolution of layers has long been a topic of interest for the terrestrial ocean, and under subsurface ocean conditions there are additional motives to study this phenomenon, as the layers can hinder heat and material transport and thus have to be taken into account when considering the evolution of the icy moons and what could be observed on the surface. We investigate the evolution of layers in a double‐diffusive convection system, where both the temperature and the concentration affect the density of the fluid. We examine the development of the first and subsequent layers, how they emerge and finally disappear, and what could prolong their lifetimes.
    Description: Key Points: Layer formation is possible in a subsurface ocean that is heated from below, enriched in salts at the bottom and fresher on top. Layering is a transient feature, but this can be long lasting if the concentration difference between the top and bottom is large. As heat and material transport is inhibited while layers exist, the subsurface ocean may not be efficient in transport.
    Description: DFG
    Description: https://doi.org/10.35003/OIT7ZO
    Keywords: ddc:523 ; subsurface oceans ; icy moons ; layering ; transport mechanism
    Language: English
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  • 48
    Publication Date: 2024-02-15
    Description: Hydraulic fracturing (HF) operations are widely associated with induced seismicity in the Western Canadian Sedimentary Basin. This study correlates injection parameters of 12,903 HF stages in the Kiskatinaw area in northeast British Columbia with an enhanced catalog containing 40,046 earthquakes using a supervised machine learning approach. It identifies relevant combinations of geological and operational parameters related to individual HF stages in efforts to decipher fault activation mechanisms. Our results suggest that stages targeting specific geological units (here, the Lower Montney formation) are more likely to induce an earthquake. Additional parameters positively correlated with earthquake likelihood include target formation thickness, injection volume, and completion date. Furthermore, the COVID‐19 lockdown may have reduced the potential cumulative effect of HF operations. Our results demonstrate the value of machine learning approaches for implementation as guidance tools that help facilitate safe development of unconventional energy technologies.
    Description: Plain Language Summary: Hydraulic fracturing (HF), a technique used in unconventional energy production, increases rock permeability to enhance fluid movement. Its use has led to an unprecedented increase of associated earthquakes in the Western Canadian Sedimentary Basin in the last decade, among other regions. Numerous studies have investigated the relationship between induced earthquakes and HF operations, but the connection between specific geological and operational parameters and earthquake occurrence is only partly understood. Here, we use a supervised machine learning approach with publicly available injection data from the British Columbia Oil and Gas Commission to identify influential HF parameters for increasing the likelihood of a specific operation inducing an earthquake. We find that geological parameters, such as the target formation and its thickness, are most influential. A small number of operational parameters are also important, such as the injected fluid volume and the operation date. Our findings demonstrate an approach with the potential to develop tools to help enable the continued development of alternative energy technology. They also emphasize the need for public access to operational data to estimate and reduce the hazard and associated risk of induced seismicity.
    Description: Key Points: We use supervised machine learning to investigate the relationship between hydraulic fracturing operation parameters and induced seismicity. Geological properties and a limited number of operational parameters predominantly influence the probability of an induced earthquake. The approach has the potential to guide detailed investigations of injection parameters critical for inducing earthquakes.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Gouvernement du Canada Natural Sciences and Engineering Research Council of Canada http://dx.doi.org/10.13039/501100000038
    Description: https://doi.org/10.5281/zenodo.5501399
    Description: https://ds.iris.edu/gmap/XL
    Description: https://files.bcogc.ca/thinclient/
    Description: https://open.canada.ca/data/en/dataset/7f245e4d-76c2-4caa-951a-45d1d2051333
    Description: https://github.com/obspy/obspy
    Description: https://github.com/eqcorrscan/EQcorrscan
    Description: https://github.com/smousavi05/EQTransformer
    Description: https://github.com/Dal-mzhang/REAL
    Description: https://scikit-learn.org/stable/
    Description: https://docs.fast.ai/
    Description: https://xgboost.readthedocs.io/en/stable/
    Description: https://github.com/slundberg/shap
    Description: https://docs.generic-mapping-tools.org/latest/
    Keywords: ddc:551.22 ; induced seismicity ; machine learning ; hydraulic fracturing
    Language: English
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  • 49
    Publication Date: 2023-09-12
    Description: Poloidal–toroidal magnetic field decomposition is a useful application of the Mie representation and the decomposition method enables us to determine the current density observationally and unambiguously in the local region of magnetic field measurement. The application and the limits of the decomposition method are tested against the Mercury magnetic field simulation in view of BepiColombo’s arrival at Mercury in 2025. The simulated magnetic field data are evaluated along the planned Mercury Planetary Orbiter (MPO) trajectories and the current system that is crossed by the spacecraft is extracted from the magnetic field measurements. Afterwards, the resulting currents are classified in terms of the established current system in the vicinity of Mercury. Graphical Abstract
    Description: österreichische forschungsförderungsgesellschaft http://dx.doi.org/10.13039/501100004955
    Description: deutsches ministerium für wirtschaft und energie
    Description: deutsche forschungs gesellschaft
    Description: Technische Universität Braunschweig (1042)
    Keywords: ddc:523 ; Poloidal–toroidal decomposition ; Magnetospheric current systems ; Capon’s method
    Language: English
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  • 50
    Publication Date: 2023-09-13
    Description: Archaeological structures built across active faults and ruptured by earthquakes have been used as markers to measure the amount of displacement caused by ground motion and thus to estimate the magnitude of ancient earthquakes. The example used in this study is the Crusader fortress at Tel Ateret (Vadum Iacob) in the Jordan Gorge, north of the Sea of Galilee, a site which has been ruptured repeatedly since the Iron Age. We use detailed laser scans and discrete element models of the fortification walls to deduce the slip velocity during the earthquake. Further, we test whether the in-situ observed deformation pattern of the walls allows quantification of the amount both sides of the fault moved and whether post-seismic creep contributed to total displacement. The dynamic simulation of the reaction of the fortification wall to a variety of earthquake scenarios supports the hypothesis that the wall was ruptured by two earthquakes in 1202 and 1759 CE. For the first time, we can estimate the slip velocity during the earthquakes to 3 and 1 m/s for the two events, attribute the main motion to the Arabian plate with a mostly locked Sinai plate, and exclude significant creep contribution to the observed displacements of 1.25 and 0.5 m, respectively. Considering a minimum long-term slip rate at the site of 2.6 mm/year, there is a deficit of at least 1.6 m slip corresponding to a potential future magnitude 7.5 earthquake; if we assume ~5 mm/year geodetic rate, the deficit is even larger.
    Description: Universität zu Köln (1017)
    Keywords: ddc:551.22 ; Archaeoseismology ; Back calculation of ground motion ; Fault slip-velocity ; Tell Ateret ; Dead sea Fault
    Language: English
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  • 51
    Publication Date: 2023-12-05
    Description: Even though micropolar theories are widely applied for engineering applications such as the design of metamaterials, applications in the study of the Earth’s interior still remain limited and in particular in seismology. This is due to the lack of understanding of the required elastic material parameters present in the theory as well as the eigenfrequency ωr which is not observed in seismic data. By showing that the general dynamic equations of the Timoshenko’s beam is a particular case of the micropolar theory we are able to connect micropolar elastic parameters to physically measurable quantities. We then present an alternative micropolar model that, based on the same physical basis as the original model, circumvents the problem of the original eigenfrequency ωr laking in seismological data. We finally validate our model with a seismic experiment and show it is relevant to explain observed seismic dispersion curves.
    Description: Westfälische Wilhelms-Universität Münster (1056)
    Keywords: ddc:551.22 ; Timoshenko beam theory ; plate theory ; Cosserat theory ; micropolar theory ; seismology
    Language: English
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  • 52
    Publication Date: 2023-08-25
    Description: The Earth-like planets and moons in our solar system have iron-rich cores, silicate mantles, and a basaltic crust. Differentiated icy moons can have a core and a mantle and an outer water–ice layer. Indirect evidence for several icy moons suggests that this ice is underlain by or includes a water-rich ocean. Similar processes are at work in the interiors of these planets and moons, including heat transport by conduction and convection, melting and volcanism, and magnetic field generation. There are significant differences in detail, though, in both bulk chemical compositions and relative volume of metal, rock and ice reservoirs. For example, the Moon has a small core [~ 0.2 planetary radii (RP)], whereas Mercury’s is large (~ 0.8 RP). Planetary heat engines can operate in somewhat different ways affecting the evolution of the planetary bodies. Mercury and Ganymede have a present-day magnetic field while the core dynamo ceased to operate billions of years ago in the Moon and Mars. Planets and moons differ in tectonic style, from plate-tectonics on Earth to bodies having a stagnant outer lid and possibly solid-state convection underneath, with implications for their magmatic and atmosphere evolution. Knowledge about their deep interiors has improved considerably thanks to a multitude of planetary space missions but, in comparison with Earth, the data base is still limited. We describe methods (including experimental approaches and numerical modeling) and data (e.g., gravity field, rotational state, seismic signals, magnetic field, heat flux, and chemical compositions) used from missions and ground-based observations to explore the deep interiors, their dynamics and evolution and describe as examples Mercury, Venus, Moon, Mars, Ganymede and Enceladus.
    Description: Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR) (4202)
    Keywords: ddc:523 ; Interior structure ; Terrestrial planets and moons ; Space exploration ; Gravity ; Rotation ; Magnetic fields ; Thermal evolution
    Language: English
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  • 53
    Publication Date: 2023-07-20
    Description: Monitoring small magnitude induced seismicity requires a dense network of seismic stations and high-quality recordings in order to precisely determine events’ hypocentral parameters and mechanisms. However, microseismicity (e.g. swarm activity) can also occur in an area where a dense network is unavailable and recordings are limited to a few seismic stations at the surface. In this case, using advanced event detection techniques such as template matching can help to detect small magnitude shallow seismic events and give insights about the ongoing process at the subsurface giving rise to microseismicity. In this paper, we study shallow microseismic events caused by hydrofracking of the PNR-2 well near Blackpool, UK, in 2019 using recordings of a seismic network which was not designed to detect and locate such small events. By utilizing a sparse network of surface stations, small seismic events are detected using template matching technique. In addition, we apply a full-waveform moment tensor inversion to study the focal mechanisms of larger events (ML 〉 1) and used the double-difference location technique for events with high-quality and similar waveforms to obtain accurate relative locations. During the stimulation period, temporal changes in event detection rate were in agreement with injection times. Focal mechanisms of the events with high-quality recordings at multiple stations indicate a strike-slip mechanism, while a cross-section of 34 relocated events matches the dip angle of the active fault.
    Description: Karlsruher Institut für Technologie (KIT) (4220)
    Description: https://earthquakes.bgs.ac.uk/data/broadband_stationbook.html
    Keywords: ddc:551.22 ; Event detection ; Microseismicity ; Source modeling ; Template matching
    Language: English
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  • 54
    Publication Date: 2023-07-20
    Description: The parameterization of the magnetospheric field contribution, generated by currents flowing in the magnetosphere is of major importance for the analysis of Mercury’s internal magnetic field. Using a combination of the Gauss and the Mie representation (toroidal–poloidal decomposition) for the parameterization of the magnetic field enables the analysis of magnetic field data measured in current carrying regions in the vicinity of Mercury. In view of the BepiColombo mission, the magnetic field resulting from the plasma interaction of Mercury with the solar wind is simulated with a hybrid simulation code and the internal Gauss coefficients for the dipole, quadrupole and octupole field are reconstructed from the data, evaluated along the prospective trajectories of the Mercury Planetary Orbiter (MPO) using Capon’s method. Especially, it turns out that a high-precision determination of Mercury’s octupole field is expectable from the future analysis of the magnetic field data measured by the magnetometer on board MPO. Furthermore, magnetic field data of the MESSENGER mission are analyzed and the reconstructed internal Gauss coefficients are in reasonable agreement with the results from more conventional methods such as the least-square fit.
    Description: Österreichische Forschungsförderungsgesellschaft http://dx.doi.org/10.13039/501100004955
    Description: Deutsches Zentrum für Luft- und Raumfahrt http://dx.doi.org/10.13039/501100002946
    Description: Technische Universität Braunschweig (1042)
    Keywords: ddc:523 ; Mie representation ; Poloidal and toroidal magnetic fields ; Thin shell approximation ; Gauss representation ; Capon’s method
    Language: English
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  • 55
    Publication Date: 2023-07-21
    Description: In the past, several destructive earthquakes have occurred in the North African Atlas Mountain ranges located along the Africa–Eurasia plate boundary. Although the region is rich with impressive archaeological sites, including those in modern Tunisia, few comprehensive archaeoseismological studies have been conducted. Historic sources account at least three damaging earthquakes in the Kairouan area in central Tunisia between AD 859 and 1041. Little is known about which faults triggered these earthquakes or the size of these events. The water supply of the city of Kairouan depended on a 32-km-long aqueduct with a large bridge (now partially collapsed) at the confluence of the de Mouta and Cherichira rivers. The original bridge of Roman construction was retrofitted twice during the Aghlabid period (AD 800–903) and probably in AD 995 during the Fatimid period. The ruined section of the bridge shows damage which might be related to the AD 859 earthquake shaking. Here, we present a detailed study of the history, the status and the damage of the Cherichira aqueduct bridge using previous historic accounts and written works, a 3D laser scan model, local geological and seismological characteristics, and include results of radiocarbon dating and a timeline of events. In addition to earthquake ground motions, we consider severe flash floods on the bridge as a potential cause of the damage. We estimate the severity of such flash floods and develop a model with 18 earthquake scenarios on local reverse and strike-slip faults with magnitudes between MW 6.1 and 7.2. While a few damage patterns might be indicative of flooding, most damage can be attributed to earthquakes. It is highly probable that the earthquake in AD 859 caused enough damage to the Aghlabid bridge to render it dysfunctional; however, to resolve the question of whether another earthquake in AD 911 or 1041 caused the complete destruction of the previously retrofitted aqueduct by the Fatimids requires dating of additional sections of the bridge.
    Description: Universität zu Köln (1017)
    Keywords: ddc:551.22 ; Archaeoseismology ; Cherichira aqueduct ; Kairouan ; Historic earthquake ; Flash flood ; Laser scan ; Dating ; Synthetic seismogram
    Language: English
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  • 56
    Publication Date: 2023-06-20
    Description: All nuclear explosions are banned by the Comprehensive Nuclear-Test-Ban Treaty. In the context of the treaty a verification regime was put into place to detect, locate, and characterize nuclear explosions at any time, by anyone and everywhere on the Earth. The International Monitoring System, which plays a key role in the verification regime, was set up by the Preparatory Commission of the Comprehensive Nuclear-Test-Ban Treaty Organization. Out of the several different monitoring techniques applied in the International Monitoring System the seismic waveform approach is the most effective and reliable technology for monitoring nuclear explosions underground. This study introduces a deterministic method of threshold monitoring that allows to asses a lower body wave magnitude limit of a potential seismic event in a certain geographical region, that can be detected by those seismic stations being part of the International Monitoring System network. The method is based on measurements of ambient seismic noise levels at the individual seismic stations along with global distance corrections terms for the body wave magnitude. The results suggest that an average global detection capability of approximately body wave magnitude 4.0 can be achieved using only stations from the primary seismic network of the International Monitoring System. The incorporation of seismic stations from the auxiliary seismic network leads to a slight improvement of the detection capability, while the use and analysis of wave arrivals from distances greater than 120∘ results in a significant improvement of the detection capability. Temporal variations in terms of hourly and monthly changes of the global detection capability can not be observed. Overall, comparisons between detection capability and manually retrieved body wave magnitudes from the Reviewed Event Bulletin suggest, that our method yields a more conservative estimation of the detection capability and that in reality detection thresholds might be even lower than estimated.
    Description: Bundesanstalt für Geowissenschaften und Rohstoffe (BGR) (4230)
    Keywords: ddc:551.22 ; International monitoring system ; seismology ; detection capability ; ambient seismic noise ; body wave magnitude correction curves
    Language: English
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  • 57
    Publication Date: 2023-06-20
    Description: An experimental multi-parameter structural monitoring system has been installed on the Kurpsai dam, western Kyrgyz Republic. This system consists of equipment for seismic and strain measurements for making longer- (days, weeks, months) and shorter- (minutes, hours) term observations, dealing with, for example seasonal (longer) effects or the response of the dam to ground motion from noise or seismic events. Fibre-optic strain sensors allow the seasonal and daily opening and closing of the spaces between the dam’s segments to be tracked. For the seismic data, both amplitude (in terms of using differences in amplitudes in the Fourier spectra for mapping the modes of vibration of the dam) and their time–frequency distribution for a set of small to moderate seismic events are investigated and the corresponding phase variabilities (in terms of lagged coherency) are evaluated. Even for moderate levels of seismic-induced ground motion, some influence on the structural response can be detected, which then sees the dam quickly return to its original state. A seasonal component was identified in the strain measurements, while levels of noise arising from the operation of the dam's generators and associated water flow have been provisionally identified.
    Description: Bundesministerium für Forschung und Technologie http://dx.doi.org/10.13039/501100004937
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:551.22 ; Structural health monitoring ; Dam engineering ; Operational and environmental effects ; Strong-motion ; Strain ; Elastic response ; Kurpsai dam
    Language: English
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  • 58
    Publication Date: 2023-06-12
    Description: Even though micropolar theories are widely applied for engineering applications such as the design of metamaterials, applications in the study of the Earth’s interior still remain limited and in particular in seismology. This is due to the lack of understanding of the required elastic material parameters present in the theory as well as the eigenfrequency $\omega _r$ which is not observed in seismic data. By showing that the general dynamic equations of the Timoshenko’s beam is a particular case of the micropolar theory we are able to connect micropolar elastic parameters to physically measurable quantities. We then present an alternative micropolar model that, based on the same physical basis as the original model, circumvents the problem of the original eigenfrequency $\omega _r$ laking in seismological data. We finally validate our model with a seismic experiment and show it is relevant to explain observed seismic dispersion curves.
    Description: Westfälische Wilhelms-Universität Münster (1056)
    Keywords: ddc:551.22 ; Timoshenko beam theory ; plate theory ; Cosserat theory ; micropolar theory ; seismology
    Language: English
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  • 59
    Publication Date: 2023-06-12
    Description: Seismic events produced by block rotations about vertical axis occur in many geodynamic contexts. In this study, we show that these rotations can be accounted for using the proper theory, namely micropolar theory, and a new asymmetric moment tensor can be derived. We then apply this new theory to the Kaikōura earthquake (2016/11/14), Mw 7.8, one of the most complex earthquakes ever recorded with modern instrumental techniques. Using advanced numerical techniques, we compute synthetic seismograms including a full asymmetric moment tensor and we show that it induces measurable differences in the waveforms proving that seismic data can record the effects of the block rotations observed in the field. Therefore, the theory developed in this work provides a full framework for future dynamic source inversions of asymmetric moment tensors.
    Description: Westfälische Wilhelms-Universität Münster (1056)
    Keywords: ddc:551.22 ; Seismology ; asymmetric moment tensor ; micropolar theory ; Kaikōura earthquake
    Language: English
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  • 60
    Publication Date: 2023-06-22
    Description: Sometimes, a rather high stress drop characterizes earthquakes induced by underground fluid injections or productions. In addition, long-term fluid operations in the underground can influence a seismogenic reaction of the rock per unit volume of the fluid involved. The seismogenic index is a quantitative characteristic of such a reaction. We derive a relationship between the seismogenic index and stress drop. This relationship shows that the seismogenic index increases with the average stress drop of induced seismicity. Further, we formulate a simple and rather general phenomenological model of stress drop of induced earthquakes. This model shows that both a decrease of fault cohesion during the earthquake rupture process and an enhanced level of effective stresses could lead to high stress drop. Using these two formulations, we propose the following mechanism of increasing induced seismicity rates observed, e.g., by long-term gas production at Groningen. Pore pressure depletion can lead to a systematic increase of the average stress drop (and thus, of magnitudes) due to gradually destabilizing cohesive faults and due to a general increase of effective stresses. Consequently, elevated average stress drop increases seismogenic index. This can lead to seismic risk increasing with the operation time of an underground reservoir.
    Description: PHASE University consortium project of Freie Universität Berlin
    Description: Freie Universität Berlin (1008)
    Keywords: ddc:551.22 ; Induced seismicity ; Hydrocarbon production ; Fluid injection ; Geo-Energy ; Seismic hazard ; Reservoir Geomechancs
    Language: English
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  • 61
    Publication Date: 2024-02-28
    Description: The AlpArray experiment and the deployment of Swath-D together with the dense permanent network in Italy allow for detailed imaging of the spatio-temporal imaging complexity of seismic wave-fields within the greater Alpine region. The distance of any point within the area to the nearest station is less than 30 km, resulting in an average inter-station distance of about 45 km. With a much denser deployment in a smaller region of the Alps (320 km in length and 140 km wide), the Swath-D network possesses an average inter-station distance of about 15 km. We show that seismogram sections with a spatial sampling of less than 5 km can be obtained using recordings of these regional arrays for just a single event. Multiply reflected body waves can be observed for up to 2 h after source time. In addition, we provide and describe animations of long-period seismic wave-fields using recordings of about 1300–1600 broadband stations for six representative earthquakes. These illustrate the considerable spatio-temporal variability of the wave-field’s properties at a high lateral resolution. Within denser station distributions like those provided by Swath-D, even shorter period body and surface wave features can be recovered. The decrease of the horizontal wavelength from P to S to surface waves, deviations from spherically symmetric wavefronts, and the capability to detect multi-orbit arrivals are demonstrated qualitatively by the presented wave-field animations, which are a valuable tool for educational, quality control, and research purposes. We note that the information content of the acquired datasets can only be adequately explored by application of appropriate quantitative methods accounting for the considerable complexity of the seismic wave-fields as revealed by the now available station configuration.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Christian-Albrechts-Universität zu Kiel (3094)
    Keywords: ddc:551.22 ; Seismology ; Wave-fields ; Animations ; Alps ; AlpArray ; Swath-D
    Language: English
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  • 62
    Publication Date: 2023-06-05
    Description: A 6 degrees-of-freedom (6DoF) sensor, measuring three components of translational acceleration and three components of rotation rate, provides the full history of motion it is exposed to. In Earth sciences 6DoF sensors have shown great potential in exploring the interior of our planet and its seismic sources. In space sciences, apart from navigation, 6DoF sensors are, up to now, only rarely used to answer scientific questions. As a first step of establishing 6DoF motion sensing deeper into space sciences, this article describes novel scientific approaches based on 6DoF motion sensing with substantial potential for constraining the interior structure of planetary objects and asteroids. Therefore we estimate 6DoF-signal levels that originate from lander–surface interactions during landing and touchdown, from a body’s rotational dynamics as well as from seismic ground motions. We discuss these signals for an exemplary set of target bodies including Dimorphos, Phobos, Europa, the Earth’s Moon and Mars and compare those to self-noise levels of state-of-the-art sensors.
    Description: Horizon 2020 http://dx.doi.org/10.13039/501100007601
    Description: Projekt DEAL
    Keywords: ddc:523 ; Planetary exploration ; Planetary seismology ; Librations ; Tides ; 6DoF sensors
    Language: English
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  • 63
    Publication Date: 2023-07-20
    Description: Natural earthquakes often have very few observable foreshocks which significantly complicates tracking potential preparatory processes. To better characterize expected preparatory processes before failures, we study stick-slip events in a series of triaxial compression tests on faulted Westerly granite samples. We focus on the influence of fault roughness on the duration and magnitude of recordable precursors before large stick–slip failure. Rupture preparation in the experiments is detectable over long time scales and involves acoustic emission (AE) and aseismic deformation events. Preparatory fault slip is found to be accelerating during the entire pre-failure loading period, and is accompanied by increasing AE rates punctuated by distinct activity spikes associated with large slip events. Damage evolution across the fault zones and surrounding wall rocks is manifested by precursory decrease of seismic b-values and spatial correlation dimensions. Peaks in spatial event correlation suggest that large slip initiation occurs by failure of multiple asperities. Shear strain estimated from AE data represents only a small fraction (〈 1%) of total shear strain accumulated during the preparation phase, implying that most precursory deformation is aseismic. The relative contribution of aseismic deformation is amplified by larger fault roughness. Similarly, seismic coupling is larger for smooth saw-cut faults compared to rough faults. The laboratory observations point towards a long-lasting and continuous preparation process leading to failure and large seismic events. The strain partitioning between aseismic and observable seismic signatures depends on fault structure and instrument resolution.
    Description: Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ http://dx.doi.org/10.13039/501100010956
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:551.22 ; Earthquakes ; rupture ; stick–slip tests ; seismic ; aseismic
    Language: English
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  • 64
    Publication Date: 2023-07-20
    Description: We use global data from the Lunar Orbiter Laser Altimeter (LOLA) to retrieve the lunar tidal Love number h2 and find h2 = 0.0387 ± 0.0025. This result is in agreement with previous estimates from laser altimetry using crossover points of LOLA profiles. The Love numbers k2 and h2 are key constraints on planetary interior models. We further develop and apply a retrieval method based on a simultaneous inversion for the topography and the tidal signal benefiting from the large volume of LOLA data. By the application to the lunar tides, we also demonstrate the potential of the method for future altimetry experiments at other planetary bodies. The results of this study are very promising with respect to the determination of Mercury’s and Ganymede’s h2 from future altimeter measurements.
    Description: DLR Space Administration
    Description: International Max Planck Research School on Solar System Science at the University of Göttingen
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:523 ; Tides ; Laser altimetry ; Lunar Orbiter Laser Altimeter ; Lunar interior
    Language: English
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  • 65
    Publication Date: 2023-06-08
    Description: Groningen is the largest onshore gas field under production in Europe. The pressure depletion of the gas field started in 1963. In 1991, the first induced micro-earthquakes have been located at reservoir level with increasing rates in the following decades. Most of these events are of magnitude less than 2.0 and cannot be felt. However, maximum observed magnitudes continuously increased over the years until the largest, significant event with ML=3.6 was recorded in 2014, which finally led to the decision to reduce the production. This causal sequence displays the crucial role of understanding and modeling the relation between production and induced seismicity for economic planing and hazard assessment. Here we test whether the induced seismicity related to gas exploration can be modeled by the statistical response of fault networks with rate-and-state-dependent frictional behavior. We use the long and complete local seismic catalog and additionally detailed information on production-induced changes at the reservoir level to test different seismicity models. Both the changes of the fluid pressure and of the reservoir compaction are tested as input to approximate the Coulomb stress changes. We find that the rate-and-state model with a constant tectonic background seismicity rate can reproduce the observed long delay of the seismicity onset. In contrast, so-called Coulomb failure models with instantaneous earthquake nucleation need to assume that all faults are initially far from a critical state of stress to explain the delay. Our rate-and-state model based on the fluid pore pressure fits the spatiotemporal pattern of the seismicity best, where the fit further improves by taking the fault density and orientation into account. Despite its simplicity with only three free parameters, the rate-and-state model can reproduce the main statistical features of the observed activity.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.22 ; Induced seismicity ; Modeling ; Statistical seismology ; Forecast
    Language: English
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  • 66
    Publication Date: 2023-06-20
    Description: The selection of ground motion models, and the representation of their epistemic uncertainty in the form of a logic tree, is one of the fundamental components of probabilistic seismic hazard and risk analysis. A new ground motion model (GMM) logic tree has been developed for the 2020 European seismic hazard model, which develops upon recently compiled ground motion data sets in Europe. In contrast to previous European seismic hazard models, the new ground model logic tree is built around the scaled backbone concept. Epistemic uncertainties are represented as calibrations to a reference model and aim to characterise the potential distributions of median ground motions resulting from variability in source scaling and attenuation. These scaled backbone logic trees are developed and presented for shallow crustal seismic sources in Europe. Using the new European strong motion flatfile, and capitalising on recent perspectives in ground motion modelling in the scientific literature, a general and transferable procedure is presented for the construction of a backbone model and the regionalisation of epistemic uncertainty. This innovative approach forms a general framework for revising and updating the GMM logic tree at national and European scale as new strong motion data emerge in the future.
    Description: Horizon 2020 http://dx.doi.org/10.13039/501100007601
    Keywords: ddc:551.22 ; Probabilistic seismic hazard assessment ; Ground motion models ; Epistemic uncertainty ; Regionalisation
    Language: English
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  • 67
    Publication Date: 2023-06-20
    Description: The simulation of broad-band (0.1 to 10 + Hz) ground-shaking over deep and spatially extended sedimentary basins at regional scales is challenging. We evaluate the ground-shaking of a potential M 6.5 earthquake in the southern Lower Rhine Embayment, one of the most important areas of earthquake recurrence north of the Alps, close to the city of Cologne in Germany. In a first step, information from geological investigations, seismic experiments and boreholes is combined for deriving a harmonized 3D velocity and attenuation model of the sedimentary layers. Three alternative approaches are then applied and compared to evaluate the impact of the sedimentary cover on ground-motion amplification. The first approach builds on existing response spectra ground-motion models whose amplification factors empirically take into account the influence of the sedimentary layers through a standard parameterization. In the second approach, site-specific 1D amplification functions are computed from the 3D basin model. Using a random vibration theory approach, we adjust the empirical response spectra predicted for soft rock conditions by local site amplification factors: amplifications and associated ground-motions are predicted both in the Fourier and in the response spectra domain. In the third approach, hybrid physics-based ground-motion simulations are used to predict time histories for soft rock conditions which are subsequently modified using the 1D site-specific amplification functions computed in method 2. For large distances and at short periods, the differences between the three approaches become less notable due to the significant attenuation of the sedimentary layers. At intermediate and long periods, generic empirical ground-motion models provide lower levels of amplification from sedimentary soils compared to methods taking into account site-specific 1D amplification functions. In the near-source region, hybrid physics-based ground-motions models illustrate the potentially large variability of ground-motion due to finite source effects.
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:551.22 ; Ground-motion modelling ; Site effects ; Scenario ; Random vibration theory ; Hybrid modelling
    Language: English
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  • 68
    Publication Date: 2023-06-20
    Description: Regions of low seismicity present a particular challenge for probabilistic seismic hazard analysis when identifying suitable ground motion models (GMMs) and quantifying their epistemic uncertainty. The 2020 European Seismic Hazard Model adopts a scaled backbone approach to characterise this uncertainty for shallow seismicity in Europe, incorporating region-to-region source and attenuation variability based on European strong motion data. This approach, however, may not be suited to stable cratonic region of northeastern Europe (encompassing Finland, Sweden and the Baltic countries), where exploration of various global geophysical datasets reveals that its crustal properties are distinctly different from the rest of Europe, and are instead more closely represented by those of the Central and Eastern United States. Building upon the suite of models developed by the recent NGA East project, we construct a new scaled backbone ground motion model and calibrate its corresponding epistemic uncertainties. The resulting logic tree is shown to provide comparable hazard outcomes to the epistemic uncertainty modelling strategy adopted for the Eastern United States, despite the different approaches taken. Comparison with previous GMM selections for northeastern Europe, however, highlights key differences in short period accelerations resulting from new assumptions regarding the characteristics of the reference rock and its influence on site amplification.
    Description: Horizon 2020 Framework Programme http://dx.doi.org/10.13039/100010661
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:551.22 ; Ground motion models ; Stable craton ; Regionalisation ; Epistemic uncertainty ; Europe
    Language: English
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  • 69
    Publication Date: 2023-06-20
    Description: To complement the new European Strong-Motion dataset and the ongoing efforts to update the seismic hazard and risk assessment of Europe and Mediterranean regions, we propose a new regionally adaptable ground-motion model (GMM). We present here the GMM capable of predicting the 5% damped RotD50 of PGA, PGV, and SA(T = 0.01 − 8 s) from shallow crustal earthquakes of 3 ≤ M W ≤ 7.4 occurring 0 〈 RJB ≤ 545 km away from sites with 90 ≤ Vs30 ≤ 3000 m s−1 or 0.001 ≤ slope ≤ 1 m m−1. The extended applicability derived from thousands of new recordings, however, comes with an apparent increase in the aleatory variability (σ). Firstly, anticipating contaminations and peculiarities in the dataset, we employed robust mixed-effect regressions to down weigh only, and not elimi nate entirely, the influence of outliers on the GMM median and σ. Secondly, we regionalised the attenuating path and localised the earthquake sources using the most recent models, to quantify region-specific anelastic attenuation and locality-specific earthquake characteristics as random-effects, respectively. Thirdly, using the mixed-effect variance–covariance structure, the GMM can be adapted to new regions, localities, and sites with specific datasets. Consequently, the σ is curtailed to a 7% increase at T 〈 0.3 s, and a sub stantial 15% decrease at T ≥ 0.3 s, compared to the RESORCE based partially non-ergodic GMM. We provide the 46 attenuating region-, 56 earthquake localities-, and 1829 site-spe cific adjustments, demonstrate their usage, and present their robustness through a 10-fold cross-validation exercise.
    Description: SIGMA2 consortium (EDF, CEA, PG&E, SwissNuclear,. Areva, CEZ, CRIEPI)
    Description: H2020 Research Infrastructures http://dx.doi.org/10.13039/100010666
    Keywords: ddc:551.22 ; Ground-motion model ; Response spectra ; Robust mixed-effects regression ; Regionally adaptable ; Seismic hazard and risk ; Europe
    Language: English
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  • 70
    Publication Date: 2023-06-20
    Description: We perform a spectral decomposition of the Fourier amplitude spectra disseminated along with the Engineering Strong Motion (ESM) flat file for Europe and Middle East. We apply a non-parametric inversion schema to isolate source, propagation and site effects, introducing a regionalization for the attenuation model into three domains. The obtained propagation and source components of the model are parametrized in terms of geometrical spreading, quality factor, seismic moment, and corner frequency assuming a ω2 source model. The non-parametric spectral attenuation values show a faster decay for earthquakes in Italy than in the other regions. Once described in terms of geometrical spreading and frequency-dependent quality factor, slopes and breakpoint locations of the piece-wise linear model for the geometrical spreading show regional variations, confirming that the non-parametric models capture the effects of crustal heterogeneities and differences in the anelastic attenuation. Since they are derived in the framework of a single inversion, the source spectra of the largest events which have occurred in Europe in the last decades can be directly compared and the scaling of the extracted source parameters evaluated. The Brune stress drop varies over about 2 orders of magnitude (the 5th, 50th and 95th percentiles of the ∆σ distribution are 0.76, 2.94, and 13.07 MPa, respectively), with large events having larger stress drops. In particular, the 5th, 50th and 95th percentiles for M 〉 5.5 are 2.87, 6.02, and 23.5 MPa, respectively whereas, for M 〈 5.5, the same percentiles are 0.73, 2.84, and 12.43 MPa. If compared to the residual distributions associated to a ground motion prediction equation previously derived using the same Fourier amplitude spectra, the source parameter and the empirical site amplification effects correlate well with the inter-event and inter-station residuals, respectively. Finally, we calibrated both non-parametric and parametric attenuation models for estimating the stress drop from the ratio between Arias intensity and significant duration. The results confirm that computing the Arias stress drop is a suitable approach for complementing the seismic moment with information controlling the source radiation at high frequencies for rapid response applications.
    Description: https://esm.mi.ingv.it//flatfile-2018/
    Keywords: ddc:551.22 ; Ground motion models ; Spectral decomposition ; Arias intensity ; Source parameters
    Language: English
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  • 71
    Publication Date: 2023-06-09
    Description: Microzonation is one of the essential tools in seismology to mitigate earthquake damage by estimating the near-surface velocity structure and developing land usage plans and intelligent building design. The number of microzonation studies increased in the last few years as induced seismicity becomes more relevant, even in low-risk areas. While of vital importance, especially in densely populated cities, most of the traditional techniques suffer from different shortcomings. The microzonation technique presented here tries to reduce the existing ambiguity of the inversion results by the combination of single-station six-component (6C) measurements, including three translational and three rotational motions, and more traditional H/V techniques. By applying this new technique to a microzonation study in the downtown area of Munich (Germany) using an iXblue blueSeis-3A rotational motion sensor together with a Nanometrics Trillium Compact seismometer, we were able to estimate Love and Rayleigh wave dispersion curves. These curves together with H/V spectral ratios are then inverted to obtain P- and S-wave velocity profiles of the upper 100 m. In addition, there is a good correlation between the estimated velocity models and borehole-derived lithology, indicating the potential of this single-station microzonation approach.
    Description: European Research Council https://doi.org/10.13039/501100000781
    Description: Bundesministerium für Wirtschaft und Energie https://doi.org/10.13039/501100006360
    Keywords: ddc:551.22 ; Microzonation ; Rotational seismology ; Ambient noise
    Language: English
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  • 72
    Publication Date: 2023-06-09
    Description: Clustering algorithms can be applied to seismic catalogs to automatically classify earthquakes upon the similarity of their attributes, in order to extract information on seismicity processes and faulting patterns out of large seismic datasets. We describe here a Python open-source software for density-based clustering of seismicity named seiscloud, based on the pyrocko library for seismology. Seiscloud is a tool to dig data out of large local, regional, or global seismic catalogs and to automatically recognize seismicity clusters, characterized by similar features, such as epicentral or hypocentral locations, origin times, focal mechanisms, or moment tensors. Alternatively, the code can rely on user-provided distance matrices to identify clusters of events sharing indirect features, such as similar waveforms. The code can either process local seismic catalogs or download selected subsets of seismic catalogs, accessing different global seismicity catalog providers, perform the seismic clustering over different steps in a flexible, easily adaptable approach, and provide results in form of declustered seismic catalogs and a number of illustrative figures. Here, the algorithm usage is explained and discussed through an application to Northern Chile seismicity.
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:551.22 ; Seismicity ; Clustering ; Location ; Moment tensor
    Language: English
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  • 73
    Publication Date: 2023-06-09
    Description: This is the editoral of a special issue that is focused on the multidisciplinary approach to cultural heritage preservation, with special care to the impact of earthquakes and their associated effects. For that, we have collected a number of representative studies involving the different research fields, each addressing the problem through a specialized methodological perspective. The final goal is to set up a common ground for interaction, highlighting the need for scientific collaboration and coordinated inter- vention. Below, we briefly summarize the main contri- butions to this special issue, which have been rationally sorted to highlight the diversity in the backgrounds of the different authors and in their methodological approaches, but at the same time to emphasize similar aspects of the addressed problematics and common objectives.
    Keywords: ddc:551.22 ; Geophysics/Geodesy ; Structural Geology ; Hydrogeology ; Geotechnical Engineering & Applied Earth Sciences
    Language: English
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  • 74
    Publication Date: 2023-06-09
    Description: Since the mid-1990s, the local seismic network of the University of Cologne has produced digital seismograms. The data all underwent a daily routine processing. For this study, we re-processed data of almost a quarter century of seismicity in the Northern Rhine Area (NRA), including the Lower Rhine Embayment (LRE) and the Eifel Mountain region (EMR). This effort included refined discrimination between tectonic earthquakes, mine-induced events, and quarry blasts. While routine processing comprised the determination of local magnitude ML, in the course of this study, source spectra-based estimates for moment magnitude MW for 1332 earthquakes were calculated. The resulting relation between ML and MW agrees well with the theory of an ML ∝ 1.5 MW dependency at magnitudes below 3. By applying Gutenberg-Richter relation, the b-value for ML was less (0.82) than MW (1.03). Fault plane solutions for 66 earthquakes confirm the previously published N118° E direction of maximum horizontal stress in the NRA. Comparison of the seismicity with recently published Global Positioning System–based deformation data of the crust shows that the largest seismic activity during the observation period in the LRE occurred in the region with the highest dilatation rates. The stress directions agree well with the trend of major faults, and declining seismicity from south to north correlates with decreasing strain rates. In the EMR, earthquakes concentrate at the fringes of the area with corresponding the largest uplift.
    Description: Projekt DEAL
    Keywords: ddc:551.22 ; Northern Rhine Area ; Lower Rhine Embayment ; Eifel ; Seismicity ; Moment magnitude ; Crustal deformation
    Language: English
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  • 75
    Publication Date: 2023-06-19
    Description: GIS-based multicriteria evaluation (MCE) provides a framework for analysing complex decision problems by quantifying variables of interest to score potential locations according to their suitability. In the context of earthquake preparedness and post-disaster response, MCE has relied mainly on uninformed or non-expert stakeholders to identify high-risk zones, prioritise areas for response, or highlight vulnerable populations. In this study, we compare uninformed, informed non-expert, and expert stakeholders’ responses in MCE modelling for earthquake response planning in Vancouver, Canada. Using medium- to low-complexity MCE models, we highlight similarities and differences in the importance of infrastructural and socioeconomic variables, emergency services, and liquefaction potential between a non-weighted MCE, a medium-complexity informed non-expert MCE, and a low-complexity MCE informed by 35 local earthquake planning and response experts from governmental and non-governmental organisations. Differences in the observed results underscore the importance of accessible, expert-informed approaches for prioritising locations for earthquake response planning and for the efficient and geographically precise allocation of resources.
    Description: Friedrich-Alexander-Universität Erlangen-Nürnberg (1041)
    Keywords: ddc:551.22 ; Multicriteria evaluation ; Earthquake ; Disaster response ; Natural hazards ; Expert knowledge ; Participatory mapping
    Language: English
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