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  • 1
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    Seismotectonics of the Blanco Transform Fault System, Northeast Pacific: Evidence for an Immature Plate Boundary (2023)
    Details
    Publikationsdatum: 2023-09-13
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: China Scholarship Council http://dx.doi.org/10.13039/501100004543
    Beschreibung: https://doi.org/10.7914/SN/X9_2012
    Beschreibung: https://www.gmrt.org/GMRTMapTool/
    Beschreibung: https://mrdata.usgs.gov/magnetic/
    Schlagwort(e): ddc:551.22 ; Blanco transform fault system ; local seismicity ; tectonic evolution ; transform plate boundary
    Sprache: Englisch
    Materialart: doc-type:article
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
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    Variation of Fault Creep Along the Overdue Istanbul‐Marmara Seismic Gap in NW Türkiye (2023)
    Details
    Publikationsdatum: 2023-12-12
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: Helmholtz Association http://dx.doi.org/10.13039/501100009318
    Beschreibung: https://doi.org/10.5880/GFZ.4.2.2023.002
    Beschreibung: http://doi.org/10.7914/SN/TU
    Beschreibung: http://doi.org/10.7914/SN/KO
    Beschreibung: http://doi.org/10.7914/SN/PZ
    Beschreibung: http://doi.org/10.7914/SN/TB
    Beschreibung: http://alomax.free.fr/nlloc/
    Beschreibung: https://www.ldeo.columbia.edu/%7Efelixw/hypoDD.html
    Beschreibung: http://doi.org/10.5281/zenodo.3407866
    Beschreibung: https://doi.org/10.1029/2019gc008515
    Schlagwort(e): ddc:551.22 ; repeating earthquakes ; Marmara Sea ; fault creep ; seismic cyle ; seismic gap
    Sprache: Englisch
    Materialart: doc-type:article
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
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    The Energetic 2022 Seismic Unrest Related to Magma Intrusion at the North Mid‐Atlantic Ridge (2023)
    Details
    Publikationsdatum: 2023-07-21
    Beschreibung: 〈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〉
    Beschreibung: 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〉
    Beschreibung: 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.
    Beschreibung: German BMBF project EWRICA
    Beschreibung: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Beschreibung: https://doi.org/10.5281/zenodo.8089070
    Schlagwort(e): ddc:551.22 ; seismic swarm ; Mid‐Atlantic Ridge ; seismicity ; magma dyke
    Sprache: Englisch
    Materialart: doc-type:article
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
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    Zur Land- und Bodendegradation – ein Rück- und Ausblick deutschland- und weltweit (2023)
    Details
    Publikationsdatum: 2023-06-12
    Beschreibung: 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.
    Beschreibung: research
    Schlagwort(e): ddc:550 ; Boden ; Landschaft ; Bodendegeneration ; Deutschland ; Anthropogene Bodenveränderung
    Sprache: Deutsch
    Materialart: doc-type:article
    Format: 9
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
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    Sea Level Changes Affect Seismicity Rates in a Hydrothermal System Near Istanbul (2023)
    Details
    Publikationsdatum: 2023-10-24
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: Helmholtz Association http://dx.doi.org/10.13039/501100009318
    Beschreibung: Alexander von Humboldt‐Stiftung http://dx.doi.org/10.13039/100005156
    Beschreibung: National Science Foundation http://dx.doi.org/10.13039/100000001
    Beschreibung: National Aeronautics and Space Administration http://dx.doi.org/10.13039/100000104
    Beschreibung: VW momentum
    Beschreibung: https://tdvms.afad.gov.tr/
    Beschreibung: http://www.koeri.boun.edu.tr/sismo/2/earthquake-catalog/
    Beschreibung: https://www.unavco.org/data/strain-seismic/bsm-data/bsm-data.html
    Schlagwort(e): ddc:551.22 ; seismicity catalog ; sea level change ; hydrothermal region ; strain ; strainmeter ; solid Earth tides
    Sprache: Englisch
    Materialart: doc-type:article
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
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    Induced Earthquake Source Parameters, Attenuation, and Site Effects From Waveform Envelopes in the Fennoscandian Shield (2023)
    Details
    Publikationsdatum: 2024-01-19
    Beschreibung: 〈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〉
    Beschreibung: 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〉
    Beschreibung: 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〉
    Beschreibung: Academy of Finland
    Beschreibung: Geophysical Instrument Pool Potsdam
    Beschreibung: Institute of Seismology
    Beschreibung: University of Helsinki
    Beschreibung: https://github.com/trichter/qopen_finland
    Beschreibung: https://doi.org/10.23729/39cfac4f-4d0d-4fb4-83dc-6f67e8ba8dce
    Beschreibung: https://doi.org/10.23729/cdfd937c-37d5-46b0-9c16-f6e0c10bc81f
    Beschreibung: https://doi.org/10.23729/6d15a5ea-7671-4bab-88a1-71f4ed962276
    Schlagwort(e): ddc:551.22 ; seismic attenuation ; wave scattering and diffraction ; induced earthquakes ; earthquake source observations ; site effects ; Fennoscandian Shield
    Sprache: Englisch
    Materialart: doc-type:article
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
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    Beamforming of Rayleigh and Love Waves in the Course of Atlantic Cyclones (2023)
    Details
    Publikationsdatum: 2024-04-03
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: German Research Foundation
    Beschreibung: https://doi.org/10.7289/V5NK3BZP
    Beschreibung: https://www.fdsn.org/networks/detail/CN/
    Beschreibung: http://ds.iris.edu/wilber3/
    Beschreibung: ftp://ftp.ifremer.fr/ifremer/ww3/HINDCAST
    Schlagwort(e): ddc:551.22 ; ambient seismic noise ; ocean microseisms ; hurricanes ; ocean gravity waves ; array seismology ; marine geophysics
    Sprache: Englisch
    Materialart: doc-type:article
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
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    Seismic and Tsunamigenic Characteristics of a Multimodal Rupture of Rapid and Slow Stages: The Example of the Complex 12 August 2021 South Sandwich Earthquake (2022)
    Details
    Publikationsdatum: 2023-11-27
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Beschreibung: Agencia Nacional de Investigación y Desarrollo http://dx.doi.org/10.13039/501100020884
    Beschreibung: https://ds.iris.edu/wilbert3/find_event
    Beschreibung: https://www.usgs.gov/natural-hazards/earthquake-hazards/lists-maps-and-statistics
    Beschreibung: http://www.ioc-sealevelmonitoring.org/
    Beschreibung: https://doi.org/10.7289/V5C8276M
    Beschreibung: https://www.gfz-potsdam.de/en/software/tsunami-wave-propagations-easywave
    Schlagwort(e): ddc:551.22 ; 2021 South Sandwich Earthquake ; seismic characteristics ; tsunamigenic characteristics
    Sprache: Englisch
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  • 9
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    A Coulomb Stress Response Model for Time‐Dependent Earthquake Forecasts (2022)
    Details
    Publikationsdatum: 2023-01-21
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: European Unions 2020 research and innovation programme
    Beschreibung: https://github.com/torstendahm/tdsr
    Schlagwort(e): ddc:551.22 ; seismicity ; physics based model ; earthquake physics
    Sprache: Englisch
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  • 10
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    Upper Plate Response to a Sequential Elastic Rebound and Slab Acceleration During Laboratory‐Scale Subduction Megathrust Earthquakes (2022)
    Details
    Publikationsdatum: 2023-01-21
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: SUBITOP Marie Sklodowska‐Curie Action project from the European Union's EU Framework Programme
    Beschreibung: Deutsche Forschungsgemeinschaft
    Beschreibung: https://doi.org/10.5880/fidgeo.2022.024
    Schlagwort(e): ddc:551.22 ; analog modeling ; megathrust earthquake ; seismic cycle ; elastic rebound ; upper plate ; overshooting
    Sprache: Englisch
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  • 11
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    Magmatic Activity and Dynamics of Melt Supply of Volcanic Centers of Ultraslow Spreading Ridges: Hints From Local Earthquake Tomography at the Knipovich Ridge (2022)
    Details
    Publikationsdatum: 2023-01-19
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Schlagwort(e): ddc:551.22 ; ultraslow spreading ; Knipovich Ridge ; local earthquake tomography ; seismicity ; mid‐ocean ridge ; partial melt area
    Sprache: Englisch
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  • 12
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    Depth‐Varying Friction on a Ramp‐Flat Fault Illuminated by ∼3‐Year InSAR Observations Following the 2017 Mw 7.3 Sarpol‐e Zahab Earthquake (2022)
    Guo, Zelong ; Motagh, Mahdi ; Hu, Jyr‐Ching ; [weitere]
    Details
    Publikationsdatum: 2024-03-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809
    Beschreibung: China Scholarship Council http://dx.doi.org/10.13039/501100004543
    Beschreibung: Ministry of Science and Technology in Taiwan
    Beschreibung: https://www.asf.alaska.edu/
    Beschreibung: http://irsc.ut.ac.ir/
    Beschreibung: https://www.globalcmt.org/
    Beschreibung: https://doi.org/10.5281/zenodo.7113073
    Schlagwort(e): ddc:551.22 ; Zagros fold thrust belt ; Sarpol-e Zahab earthquake ; postseismic observations ; postseismic deformation ; InSAR
    Sprache: Englisch
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  • 13
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    Small Magnitude Events Highlight the Correlation Between Hydraulic Fracturing Injection Parameters, Geological Factors, and Earthquake Occurrence (2022)
    Details
    Publikationsdatum: 2024-02-15
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Beschreibung: Gouvernement du Canada Natural Sciences and Engineering Research Council of Canada http://dx.doi.org/10.13039/501100000038
    Beschreibung: https://doi.org/10.5281/zenodo.5501399
    Beschreibung: https://ds.iris.edu/gmap/XL
    Beschreibung: https://files.bcogc.ca/thinclient/
    Beschreibung: https://open.canada.ca/data/en/dataset/7f245e4d-76c2-4caa-951a-45d1d2051333
    Beschreibung: https://github.com/obspy/obspy
    Beschreibung: https://github.com/eqcorrscan/EQcorrscan
    Beschreibung: https://github.com/smousavi05/EQTransformer
    Beschreibung: https://github.com/Dal-mzhang/REAL
    Beschreibung: https://scikit-learn.org/stable/
    Beschreibung: https://docs.fast.ai/
    Beschreibung: https://xgboost.readthedocs.io/en/stable/
    Beschreibung: https://github.com/slundberg/shap
    Beschreibung: https://docs.generic-mapping-tools.org/latest/
    Schlagwort(e): ddc:551.22 ; induced seismicity ; machine learning ; hydraulic fracturing
    Sprache: Englisch
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  • 14
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    Reconstructing the slip velocities of the 1202 and 1759 CE earthquakes based on faulted archaeological structures at Tell Ateret, Dead Sea Fault (2021)
    Springer Netherlands
    Details
    Publikationsdatum: 2023-09-13
    Beschreibung: 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.
    Beschreibung: Universität zu Köln (1017)
    Schlagwort(e): ddc:551.22 ; Archaeoseismology ; Back calculation of ground motion ; Fault slip-velocity ; Tell Ateret ; Dead sea Fault
    Sprache: Englisch
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  • 15
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    Understanding Micropolar Theory in the Earth Sciences I: The Eigenfrequency ωr (2021)
    Springer International Publishing
    Details
    Publikationsdatum: 2023-12-05
    Beschreibung: 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.
    Beschreibung: Westfälische Wilhelms-Universität Münster (1056)
    Schlagwort(e): ddc:551.22 ; Timoshenko beam theory ; plate theory ; Cosserat theory ; micropolar theory ; seismology
    Sprache: Englisch
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  • 16
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    Induced seismicity due to hydraulic fracturing near Blackpool, UK: source modeling and event detection (2021)
    Springer Netherlands
    Details
    Publikationsdatum: 2023-07-20
    Beschreibung: 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.
    Beschreibung: Karlsruher Institut für Technologie (KIT) (4220)
    Beschreibung: https://earthquakes.bgs.ac.uk/data/broadband_stationbook.html
    Schlagwort(e): ddc:551.22 ; Event detection ; Microseismicity ; Source modeling ; Template matching
    Sprache: Englisch
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  • 17
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    Archaeoseismological study of the Cherichira aqueduct bridge, Kairouan, Tunisia (2021)
    Springer International Publishing
    Details
    Publikationsdatum: 2023-07-21
    Beschreibung: 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.
    Beschreibung: Universität zu Köln (1017)
    Schlagwort(e): ddc:551.22 ; Archaeoseismology ; Cherichira aqueduct ; Kairouan ; Historic earthquake ; Flash flood ; Laser scan ; Dating ; Synthetic seismogram
    Sprache: Englisch
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  • 18
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    Performance of the International Monitoring System Seismic Network Based on Ambient Seismic Noise Measurements (2021)
    Springer International Publishing
    Details
    Publikationsdatum: 2023-06-20
    Beschreibung: 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.
    Beschreibung: Bundesanstalt für Geowissenschaften und Rohstoffe (BGR) (4230)
    Schlagwort(e): ddc:551.22 ; International monitoring system ; seismology ; detection capability ; ambient seismic noise ; body wave magnitude correction curves
    Sprache: Englisch
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  • 19
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    Long- and Short-Term Monitoring of a Dam in Response to Seasonal Changes and Ground Motion Loading: The Test Case of the Kurpsai Dam, Western Kyrgyz Republic (2021)
    Springer International Publishing
    Details
    Publikationsdatum: 2023-06-20
    Beschreibung: 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.
    Beschreibung: Bundesministerium für Forschung und Technologie http://dx.doi.org/10.13039/501100004937
    Beschreibung: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Schlagwort(e): ddc:551.22 ; Structural health monitoring ; Dam engineering ; Operational and environmental effects ; Strong-motion ; Strain ; Elastic response ; Kurpsai dam
    Sprache: Englisch
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  • 20
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    Understanding Micropolar Theory in the Earth Sciences I: The Eigenfrequency $\omega_r$ (2021)
    Springer International Publishing
    Details
    Publikationsdatum: 2023-06-12
    Beschreibung: 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.
    Beschreibung: Westfälische Wilhelms-Universität Münster (1056)
    Schlagwort(e): ddc:551.22 ; Timoshenko beam theory ; plate theory ; Cosserat theory ; micropolar theory ; seismology
    Sprache: Englisch
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  • 21
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    Understanding Micropolar Theory in the Earth Sciences II: The Seismic Moment Tensor (2021)
    Springer International Publishing
    Details
    Publikationsdatum: 2023-06-12
    Beschreibung: 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.
    Beschreibung: Westfälische Wilhelms-Universität Münster (1056)
    Schlagwort(e): ddc:551.22 ; Seismology ; asymmetric moment tensor ; micropolar theory ; Kaikōura earthquake
    Sprache: Englisch
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  • 22
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    Stress Drop, Seismogenic Index and Fault Cohesion of Fluid-Induced Earthquakes (2021)
    Springer Vienna
    Details
    Publikationsdatum: 2023-06-22
    Beschreibung: 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.
    Beschreibung: PHASE University consortium project of Freie Universität Berlin
    Beschreibung: Freie Universität Berlin (1008)
    Schlagwort(e): ddc:551.22 ; Induced seismicity ; Hydrocarbon production ; Fluid injection ; Geo-Energy ; Seismic hazard ; Reservoir Geomechancs
    Sprache: Englisch
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  • 23
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    Imaging seismic wave-fields with AlpArray and neighboring European networks (2021)
    Springer Berlin Heidelberg
    Details
    Publikationsdatum: 2024-02-28
    Beschreibung: 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.
    Beschreibung: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Beschreibung: Christian-Albrechts-Universität zu Kiel (3094)
    Schlagwort(e): ddc:551.22 ; Seismology ; Wave-fields ; Animations ; Alps ; AlpArray ; Swath-D
    Sprache: Englisch
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  • 24
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    Seismic and Aseismic Preparatory Processes Before Large Stick–Slip Failure (2020)
    Springer International Publishing
    Details
    Publikationsdatum: 2023-07-20
    Beschreibung: 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.
    Beschreibung: Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ http://dx.doi.org/10.13039/501100010956
    Beschreibung: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Schlagwort(e): ddc:551.22 ; Earthquakes ; rupture ; stick–slip tests ; seismic ; aseismic
    Sprache: Englisch
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  • 25
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    Stress-based, statistical modeling of the induced seismicity at the Groningen gas field, The Netherlands (2020)
    Springer Berlin Heidelberg
    Details
    Publikationsdatum: 2023-06-08
    Beschreibung: 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.
    Beschreibung: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Beschreibung: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Schlagwort(e): ddc:551.22 ; Induced seismicity ; Modeling ; Statistical seismology ; Forecast
    Sprache: Englisch
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  • 26
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    A regionally-adaptable “scaled backbone” ground motion logic tree for shallow seismicity in Europe: application to the 2020 European seismic hazard model (2020)
    Springer Netherlands
    Details
    Publikationsdatum: 2023-06-20
    Beschreibung: 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.
    Beschreibung: Horizon 2020 http://dx.doi.org/10.13039/501100007601
    Schlagwort(e): ddc:551.22 ; Probabilistic seismic hazard assessment ; Ground motion models ; Epistemic uncertainty ; Regionalisation
    Sprache: Englisch
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  • 27
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    Regional broad-band ground-shaking modelling over extended and thick sedimentary basins: an example from the Lower Rhine Embayment (Germany) (2020)
    Springer Netherlands
    Details
    Publikationsdatum: 2023-06-20
    Beschreibung: 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.
    Beschreibung: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Schlagwort(e): ddc:551.22 ; Ground-motion modelling ; Site effects ; Scenario ; Random vibration theory ; Hybrid modelling
    Sprache: Englisch
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  • 28
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    A ground motion logic tree for seismic hazard analysis in the stable cratonic region of Europe: regionalisation, model selection and development of a scaled backbone approach (2020)
    Springer Netherlands
    Details
    Publikationsdatum: 2023-06-20
    Beschreibung: 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.
    Beschreibung: Horizon 2020 Framework Programme http://dx.doi.org/10.13039/100010661
    Beschreibung: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Schlagwort(e): ddc:551.22 ; Ground motion models ; Stable craton ; Regionalisation ; Epistemic uncertainty ; Europe
    Sprache: Englisch
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  • 29
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    A regionally-adaptable ground-motion model for shallow crustal earthquakes in Europe (2020)
    Springer Netherlands
    Details
    Publikationsdatum: 2023-06-20
    Beschreibung: 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.
    Beschreibung: SIGMA2 consortium (EDF, CEA, PG&E, SwissNuclear,. Areva, CEZ, CRIEPI)
    Beschreibung: H2020 Research Infrastructures http://dx.doi.org/10.13039/100010666
    Schlagwort(e): ddc:551.22 ; Ground-motion model ; Response spectra ; Robust mixed-effects regression ; Regionally adaptable ; Seismic hazard and risk ; Europe
    Sprache: Englisch
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    Spectral decomposition of the Engineering Strong Motion (ESM) flat file: regional attenuation, source scaling and Arias stress drop (2020)
    Springer Netherlands
    Details
    Publikationsdatum: 2023-06-20
    Beschreibung: 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.
    Beschreibung: https://esm.mi.ingv.it//flatfile-2018/
    Schlagwort(e): ddc:551.22 ; Ground motion models ; Spectral decomposition ; Arias intensity ; Source parameters
    Sprache: Englisch
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    Single-station seismic microzonation using 6C measurements (2020)
    Springer Netherlands
    Details
    Publikationsdatum: 2023-06-09
    Beschreibung: 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.
    Beschreibung: European Research Council https://doi.org/10.13039/501100000781
    Beschreibung: Bundesministerium für Wirtschaft und Energie https://doi.org/10.13039/501100006360
    Schlagwort(e): ddc:551.22 ; Microzonation ; Rotational seismology ; Ambient noise
    Sprache: Englisch
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    Seiscloud, a tool for density-based seismicity clustering and visualization (2020)
    Springer Netherlands
    Details
    Publikationsdatum: 2023-06-09
    Beschreibung: 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.
    Beschreibung: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Schlagwort(e): ddc:551.22 ; Seismicity ; Clustering ; Location ; Moment tensor
    Sprache: Englisch
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    Cultural heritage and earthquakes: bridging the gap between geophysics, archaeoseismology and engineering (2020)
    Springer Netherlands
    Details
    Publikationsdatum: 2023-06-09
    Beschreibung: 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.
    Schlagwort(e): ddc:551.22 ; Geophysics/Geodesy ; Structural Geology ; Hydrogeology ; Geotechnical Engineering & Applied Earth Sciences
    Sprache: Englisch
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    Seismicity in the Northern Rhine Area (1995–2018) (2020)
    Springer Netherlands
    Details
    Publikationsdatum: 2023-06-09
    Beschreibung: 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.
    Beschreibung: Projekt DEAL
    Schlagwort(e): ddc:551.22 ; Northern Rhine Area ; Lower Rhine Embayment ; Eifel ; Seismicity ; Moment magnitude ; Crustal deformation
    Sprache: Englisch
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  • 35
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    GIS-based multicriteria evaluation for earthquake response: a case study of expert opinion in Vancouver, Canada (2020)
    Springer Netherlands
    Details
    Publikationsdatum: 2023-06-19
    Beschreibung: 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.
    Beschreibung: Friedrich-Alexander-Universität Erlangen-Nürnberg (1041)
    Schlagwort(e): ddc:551.22 ; Multicriteria evaluation ; Earthquake ; Disaster response ; Natural hazards ; Expert knowledge ; Participatory mapping
    Sprache: Englisch
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