ALBERT

Description: S"SUB g"-amplitudes and periods of 252 European seismic events recorded at GDR and Czechoslovak seismological stations have been measured and their dependence on distance (up to 650km) and azimuth has been analyzed. These will allow reliable local and regional magnitude determination.-after Authors

Description: An analysis of the steady-state heat conduction model for the Earth's crust and the upper mantle revealed that the main difficulties in the downward continuation of subsurface geothermal measurements q were connected with an estimation of the heat flow density q"SUB M" at the Moho boundary and of the source distribution f. Solving the steady-state heat conduction equation numerically by means of finite differences (finite elements), we can describe the relation between q, q"SUB M" and f by a linear algebraic system. To overcome the non-uniqueness and instability, a least squares approach is suggested to solve these systems. Bounds for the square-means of the unknown parameters q"SUB M" and f are introduced, whereby it is possible to find solutions with appropriate mean properties. A two-dimensional geothermal profile crossing Central Europe is used to demonstrate this method. The difficulties in estimating reasonable mantle heat flow density and optimal heat source models from geothermal measurements only are pointed out.-Authors

Description: In recent years the need for improved seismic risk evaluations in Sweden has led to accurate estimates of detection porbabilities with respect to weak Swedish earthquakes. Generally, these rather low-magnitude events (M"SUB l"4) are recorded only by means of the Swedish Seismograh Station Network (SSSN), currently consisting of 6 permanent stations. Only occasionally do neighbouring Finnish and/or Norwegian stations also contribute with arrival-time readings, hence, for weak regional events, we lack usual reference system of organisations like ISC, NEIS, or EMSC when estimating the detection performance of the SSSN-stations. The main objective of the present short communication is to indicate the ability of the SSSN to detect earthquakes in Sweden and the relative detection contributions from individual network stations. The data used comprise 121 earthquakes located within Sweden and adjacent waters (Wahlström 1978). The statistical model used and other theoretical aspects of the modified approach are discussed in an earlier paper.-Authors

Description: During the period of January 1977 to December 1979, 22 earthquakes were recorded and located in Sweden and/or adjacent waters by means of the Swedish Seismograph Station Network (SSSN). 8 were felt by residents in the repective areas and hence provide an opportunity for macroseismic investigations. Such investigations are extremely useful for estimating e.g. the depth of rupture and local ground accelerations, especially when teleseismic data and strong-motion records are not available. The long-term average gives approximately 3 earthquakes per year which are reported to be felt by people. In this respect, the seismic activity in Sweden during the years under review is well within the 'normal'. The main objective of the present study is to summarize and interpret available macroseismic observations collected at the Seismological Dept in Uppsala.-P.N.Chroston

Description: The unique solvability of the inverse gravimetric problem for systems of point masses arbitrarily distributed in a bounded region is proved. Using the equivalence of this statement to the linear independence of the corresponding Newtonian potentials for single point masses this proof can be given by means of a generalized momentum representation both in modern potential theory and in classical algebraical manner.-Authors

Description: Additional keywords: Maxwell body, standard linear solid, absorption band model, seismicity, earthquake migration, plate tectonics, seismic hazard, rupture planes, source parameters, Rheologie, Schichten, Dislokationen, Neigungen, numerische Modelle, Kolumbien, Tuerkei, Nordanatolische Verwerfung, Maxwell-Koerper, Zener, tektonische Spannungen, Seismizitaet, Platten-Tektonik, Erdbeben-Gefaehrdung, Erdbeben-Serie

Description: The Institute of Seismology, University of Helsinki (ISUH) was founded in 1961 as a response to the growing public concern for environmental hazards caused by nuclear weapon testing. Since then ISUH has been responsible for seismic monitoring in Finland. The current mandate covers government regulator duties in seismic hazard mitigation and nuclear test ban treaty verification, observatory activities and operation of the Finnish National Seismic Network (FNSN) as well as research and teaching of seismology at the University of Helsinki. The first seismograph station of Finland was installed at the premises of the Department of Physics, University of Helsinki in 1924. However, the mechanical Mainka seismographs had low magnification and thus the recordings were of little practical value for the study of local seismicity. The first short-period seismographs were set up between 1956 and 1963. The next significant upgrade of FNSN occurred during the late 1970’s when digital tripartite arrays in southern and central Finland became fully operational, allowing for systematic use of instrumental detection, location and magnitude determination methods. By the end of the 1990’s, the entire network was operating using digital telemetric or dial-up methods. The FNSN has expanded significantly during the 21st Century. It comprises now 36 permanent stations. Most of the stations have Streckeisen STS-2, Nanometrics Trillium (Compact/P/PA/QA) or Guralp CMG-3T broad band sensors. Some Teledyne-Geotech S13/GS13 short period sensors are also in use. Data acquisition systems are a combination of Earth Data PS6-24 digitizers and PC with Seiscomp/Seedlink software or Nanometrics Centaurs. The stations are connected to the ISUH with Seedlink via Internet and provide continuous waveform data at 40 Hz (array) or 100-250 Hz sampling frequency. Further information about instrumentation can be found at the Institute’s web site (www.seismo.helsinki.fi). Waveform data is available from the GEOFON data centre.

Description: The evolution at the W margin of the E Antarctic platforms started with a Precambrian flyschoid formation which is overlain discordantly by Middle Cambrian limestones of an epicontinental environment and which leads to continental sedimentation conditions with acid, subsequent volcanic rocks of probably Cambrian age. A coarsely clastic red molasse without volcanic rocks of probably Upper Devonian age follows. The following evolution in Upper Paleozoic with continuation of the platform character is very incomplete. Tillites of probably Carboniferous age and Permian sandstone-siltstone interstratifications with coal intercalations are known. Structurally a historic, disharmonically superimposed stockwork structure can be detected. The processes of metamorphism which are connected with the Beardmore tectonogenesis at the turn of Precambrian/Cambrian took place in the range of the 'very low metamorphism'. With the younger, intraPaleozoic deformations no regional metamorphism is connected. Deformations which are connected with faults are of different character. Here the degree of biotite formation can be reached. -from Current Antarctic Literature

Description: Presents the time dependence of the statistical parameters alpha and beta describing seismic activity with a high time resolution. alpha stands for temporal event intensity and beta determines the distribution of magnitudes. It was studied whether these parameters are indicative as precursory phenomena predicting large aftershocks within the investigated earthquake sequences (Friuli region in 1976 and a section of the Montenegro sequence in 1979). No precursor effect could be found in the b-value of the quasi-linear Gutenberg-Richter model. b is decreasing abruptly exactly in that point when the computation window includes that large event which shall be found.-from Authors

Description: The spherical harmonic expansion of the earth's gravitational field has been obtained to degree 180 by combining several sources of data. The first data set was an a priori set of potential coefficients to degree 36 based on a number of recent solutions including a substantial of resonance terms. A second data set was a 1 x 1 deg anomaly field derived from the Seasat data set, while the third data set was an updated 1 x 1 deg terrestrial field. The last two fields were combined into one set containing 56761 1 x 1 deg values. The remaining values were computed from the a priori potential coefficients. A rigorous combination solution was not carried out. Instead all anomalies were weighted in such a way that the normal equations were diagonal. The results of the adjustment were 64800 1 x 1 deg anomalies that were expanded into spherical harmonics using the optimum quadrature procedures developed by Colombo. Accuracy estimates for each coefficient were obtained considering noise propagation and sampling error caused by the finite block size in which the anomalies are given. The percentage error of the solution reaches 100% near degree 120. The coefficients and their accuracy to degree 50 are listed in an appendix.

Description: Kartographisch überarb. Neuaufl. 2001: J. Negendank ; T. Sommer (GeoForschungsZentrum GFZ Potsdam). - Beilage zu: Trier und Umgebung / Jörg F. W. Negendank. - (Sammlung geologischer Führer ; 60)

Description: A recent series of Swedish earthquakes at a focal depth not exceeding 2-3km, the largest with I"SUB O" = V+ (MSK scale) and M"SUB L" = 3.2 shows that relatively strong seismic activity can occur in the uppermost part of the Baltic Shield. During the last 15 years several near-surface earthquakes have occurred in this region, as indicated by recorded Rg-waves and/or macroseismic data. Many events are located along the coast of central Sweden, suggesting a seismic belt of minor, near-surface activity, which should be considered in connection with the radioactive waste storage in the Swedish bedrock. The appearance of Rg, common in seismic records of explosions and rockbursts, is not a sufficient discriminator between artificial events and earthquakes. -Author

Description: Station corrections have been introduced into the M"SUB L"-scale hitherto used for Baltic Shield earthquakes. The new formula is valid for Benioff and Grenet seismograph stations in Finland and Sweden. An extension of the magnitude scale to distances as small as 30 km is made by adding the constant 0.31 to the equation. Correlating the instrumental magnitude with macroseismic parameters, a relationship between the radius of areas of perceptibility (km) and maximum intensity has been obtained which is especially useful in quantification of historical earthquakes. For stations of the Finnish Seismic Array (FINSA) equipped with Geotech S13 seismographs, formulae has been obtained from which magnitudes may now be assigned to weak shocks, which were not possible to quantify previously. -from Authors

Description: Using data from explosions recorded by the Swedish Seismograph Station Network (SSSN), an average model of two horizontal layers was deduced for the Swedish crust: Layer thicknesses (km): top layer = 10, whole crust = 37; wave velocities (km s"SUP -1"): Pn = 7.87, P"SUP *" = 6.69, Pgl = 6.27, Sn = 4.55, S"SUP *" = 3.69, Sg1 = 3.54, Sg2 = 3.40, Rg = 2.81. A computer program was developed to determine locations of regional seismic events. Assuming a horizontal two-layered crust, arrival times of identified crustal and Moho-refracted waves are given as input. The location accuracy of seismic events using three-dimensional geophone networks was investigated for real and fictitious networks and events. The effects of arrival time and velocity model accuracies, computational method, network geometry and relative location of hypocentre to geophones are quantitatively demonstrated in various examples. - from Author

Description: On February 13, 1981, a relatively strong earthquake occurred in the Lake Vanern region in south-central Sweden. The shock had a magnitude of M"SUB L" = 3.3 and was followed within three weeks by three aftershocks, with magnitudes 0.5 = or 〈 M"SUB L" = or 〈 1.0. The focal mechanism solution of the main shock indicates reverse faulting with a strike in the N-S or NE-SW direction and a nearly horizontal compressional stress. The aftershocks were too small to yield data for a full mechanism solution, but first motions of P-waves, recorded at two stations, are consistent for the aftershocks. Dynamic source parameters, derived from Pg- and Sg- wave spectra, show similar stress drops for the main shock (2 bar) and the aftershocks (1 bar), while the differences in seismic moment (1.5X10"SUP 20" resp. 4X10"SUP 18" dyne cm), fault length (0.7 resp. 0.2 km) and relative displacement (0.15 resp. 0.03 cm) are significant.-Authors

Description: To detect and to locate the frequently occurring rockbursts within the mining area at Grangesberg, Sweden, the mining company has installed a local network of geophones. Mathematical technique is presented for hypocentre determination assuming a constant velocity model and a three-dimensional network of geophones with high-speed recording. Two sets of input data are feasible: 1) relative P arrival times; 2) S minus P arrival times. The former set requires readings from at least five geophones; for the latter readings from four geophones are sufficient. Factors influencing the resulting location accuracy are studied in various examples. General conclusions and recommendations are given.-Author

Description: The results of the collection and revision of the seismicity data are presented for the territory of the GDR depicted in epicentral maps. A new map of maximum observed intensities was compiled on the basis of the reinterpretation of the strongest seismic event since 1500, the earthquake of March 6, 1982. -Authors

Description: Raw, SEGY and other supplementary data are presented from the seismic refraction / wide-angle reflection profile, TTZ-South, in Poland and Ukraine. The purpose of this 550 km long seismic profile was to reveal the lithospheric structure along the Teisseyre-Tornquist Zone (TTZ), a major geophysical boundary in Europe.

Description: Due to the major role of greenhouse gas emissions in global climate change, the development of non-fossil energy technologies is essential. Deep geothermal energy represents such an alternative, which offers promising properties such as a high base load capability and a large untapped potential. The present work addresses barite precipitation within geothermal systems and the associated reduction in rock permeability, which is a major obstacle to maintaining high efficiency. In this context, hydro-geochemical models are essential to quantify and predict the effects of precipitation on the efficiency of a system. The objective of the present work is to quantify the induced injectivity loss using numerical and analytical reactive transport simulations. For the calculations, the fractured-porous reservoirs of the German geothermal regions North German Basin (NGB) and Upper Rhine Graben (URG) are considered. Similar depth-dependent precipitation potentials could be determined for both investigated regions (2.8-20.2 g/m3 fluid). However, the reservoir simulations indicate that the injectivity loss due to barite deposition in the NGB is significant (1.8%-6.4% per year) and the longevity of the system is affected as a result; this is especially true for deeper reservoirs (3000 m). In contrast, simulations of URG sites indicate a minor role of barite (〈 0.1%-1.2% injectivity loss per year). The key differences between the investigated regions are reservoir thicknesses and the presence of fractures in the rock, as well as the ionic strength of the fluids. The URG generally has fractured-porous reservoirs with much higher thicknesses, resulting in a greater distribution of precipitates in the subsurface. Furthermore, ionic strengths are higher in the NGB, which accelerates barite precipitation, causing it to occur more concentrated around the wellbore. The more concentrated the precipitates occur around the wellbore, the higher the injectivity loss. In this work, a workflow was developed within which numerical and analytical models can be used to estimate and quantify the risk of barite precipitation within the reservoir of geothermal systems. A key element is a newly developed analytical scaling score that provides a reliable estimate of induced injectivity loss. The key advantage of the presented approach compared to fully coupled reservoir simulations is its simplicity, which makes it more accessible to plant operators and decision makers. Thus, in particular, the scaling score can find wide application within geothermal energy, e.g., in the search for potential plant sites and the estimation of long-term efficiency.

Description: Aufgrund der tragenden Rolle der Treibhausgasemissionen für den globalen Klimawandel ist die Entwicklung von nicht-fossilen Energietechnologien essenziell. Die Tiefengeothermie stellt eine solche Alternative dar, welche vielversprechende Eigenschaften wie eine hohe Grundlastfähigkeit und ein großes ungenutztes Potenzial bietet. Die vorliegende Arbeit befasst sich mit Barytausfällungen inner- halb geothermaler Systeme und der damit einhergehenden Verringerung der Gesteinsdurchlässigkeit, welche ein Haupthindernis für die Aufrechterhaltung einer hohen Effizienz darstellen. Dabei sind hydro-geochemische Modelle unerlässlich, um die Auswirkungen von Ausfällungen auf die Effizienz eines Systems zu quantifizieren und vorherzusagen. Ziel der vorliegenden Arbeit ist es, mittels numerischer und analytischer reaktiver Transportsimulationen, den induzierten Injektivitätsverlust zu quantifizieren. Für die Berechnungen werden die klüftig-porösen Reservoire der deutschen Geothermieregionen Norddeutsches Becken (NDB) und Oberrheingraben (ORG) betrachtet. Für beide untersuchte Regionen konnte ein ähnliches, tiefenabhängiges Fällungspotenzial bestimmt werden (2,8–20,2 g/m3 Fluid). Die Reservoirsimulationen zeigen jedoch, dass der Injektivitätsverlust aufgrund von Barytablagerungen im NDB erheblich ist (1,8%–6,4% pro Jahr) und die Langlebigkeit der Anlage dadurch beeinträchtigt wird, dies gilt insbesondere für tiefere Reservoire (3000 m). Im Gegensatz dazu deuten die Simulationen der ORG-Standorte auf eine untergeordnete Rolle von Baryt hin (〈 0,1%–1,2% Injektivitätsverlust pro Jahr). Die entscheidenden Unterschiede zwischen den untersuchten Regionen sind die Reservoirmächtigkeiten und das Vorhandensein von Rissen im Gestein sowie die Ionenstärke der Fluide. Der ORG weist in der Regel klüftig-poröse Reservoire mit deutlich höheren Mächtigkeiten auf, was zu einer größeren Verteilung der Präzipitate im Untergrund führt. Weiterhin sind die Ionenstärken im NDB höher, was die Barytausfällung beschleunigt und diese dadurch konzentrierter um das Bohrloch herum entstehen lässt. Je konzentrierter die Präzipitate um die Bohrung herum auftreten, desto höher ist der Injektivitätsverlust. In dieser Arbeit wurde ein Workflow erarbeitet, innerhalb dessen mittels numerischer und analytischer Modelle das Risiko von Barytausfällungen innerhalb des Reservoirs geothermischer Systeme abgeschätzt und quantifiziert werden kann. Ein zentrales Element ist ein neu entwickelter, analytischer Scaling-Score, der eine zuverlässige Schätzung des induzierten Injektivitätsverlustes ermöglicht. Der entscheidende Vorteil des präsentierten Ansatzes im Vergleich zu voll-gekoppelten Reservoirsimulationen liegt in ihrer Einfachheit, die sie für Anlagenbetreiber und Entscheidungsträger zugänglicher macht. Somit kann insbesondere der Scaling-Score eine breite Anwendung innerhalb der Geothermie finden, z.B. bei der Suche nach potenziellen Anlagenstandorten und der Abschätzung der langfristigen Effizienz.

Description: The current western margin of the South American continent is an active subduction orogeny, which is famous for the ’Andean-type’ subduction. The Andes orogeny extends more than 6000 km along the margin. The Central Andes is governed by plateau-style deformation and the subduction of the Nazca plate below Chile and western Argentina, which has caused drastic crustal shortening and thickening, magmatism and periodical back-arc lithosphere and lower crust delamination. The deformation is also influenced by the periodical dip angle variations of the Nazca plate. However, the interaction zone between the overriding plate and the subducting Nazca slab is still enigmatic. In my dissertation, I use earthquake multi-scale full waveform inversion (FWI) to image the crust and upper mantle structure providing new robust images to resolve the interactions between the slab and the Central Andean plateau. First, I performed FWI using 117 earthquakes to investigate the seismic structure for the northern Central Andes which cover the normal-dip subduction zone from southern Peru to central Chile, proceeding from long period data (40–80 s) over several steps down to 12–60 s. In this study, the subducting Nazca slab is clearly imaged in the upper mantle, with dip-angle variations from the north to the south. Bands of low velocities in the crust and mantle wedge indicate intense crustal partial melting and hydration of the mantle wedge beneath the frontal volcanic arc, respectively. They are also linked to the vigorous dehydration from the subducting Nazca plate and intermediate-depth seismicity within the slab. These low-velocity bands are interrupted at 19.8 –21 S, both in the crust and uppermost mantle with an absence of active volcanoes, hinting at the lower extent of crustal partial melting and hydration of the mantle wedge, associated with the weak dehydration from the Nazca plate. The variation of lithospheric high-velocity anomalies below the backarc from north to south allows insight into the evolutionary foundering stages of the Central Andes. An extended high-velocity layer at lithospheric depths beneath the southern Altiplano suggests underthrusting of the leading edge of the Brazilian Shield following the removal of the autochthonous lithosphere. In contrast, a steeply westward dipping high-velocity block and low-velocity lithospheric uppermost mantle beneath the southern Puna plateau hints at the ongoing lithospheric delamination. Second, I took advantage of 134 events to perform FWI and started from even longer period data 60- 120 s to 12-100 s. In this study, a new seismic velocity model for the southern Central Andes is derived, covering the Pampean flat and adjacent Payenia steep subduction segments. Strong focused crustal low-velocity anomalies indicate partial melts in the Payenia segment along the volcanic arc, whereas weaker low-velocity anomalies covering a wide zone in Pampean possibly indicate remnant melts in the past. Thinning and tearing of the flat Nazca slab below the Pampean is inferred by gaps in the high-velocity slab along the inland projection of the Juan-Fernandez-Ridge. A high-velocity anomaly in the upper mantle below the flat slab is interpreted as a relic Nazca slab segment, which indicates an earlier slab break-off during the flattening process, triggered by the buoyancy of the Juan-Fernandez-Ridge. In Payenia, large-scale low-velocity anomalies atop and below the re-steepened Nazca slab are associated with the re-opening of the mantle wedge and sub-slab asthenospheric flow, respectively.

Description: The Scandes mountain range along the western rim of the Archean Baltic craton with elevation up to 2500 m forms an exceptional setting as the orogeny terminated 420 Ma ago and the Caledonides were deeply eroded afterwards. Since this region lacks recent compressional tectonic forces, a comprehensive explanation for the topography, which shows north-south and lateral variations along the Scandes, is missing. In my dissertation, I use earthquake surface waves and ambient noise to image the crustal and mantle structure aiming to provide new clues about the topography’s origin. The focus is also on exploring structural differences between the various tectonic domains. Here, I benefit from the seismic recordings by the ScanArray network supplemented by permanent and previous projects, distributed over entire Scandinavia. First, I performed a beamforming of Rayleigh surface waves which yielded average phase velocities for the study region and several of its sub-regions. An unusual 360° or sin(1θ) phase velocity variation with propagation azimuth is observed in northern Scandinavia and southern Norway/Sweden but not in the central area. For periods 〉35 s, a 5% variation between the maximum and minimum velocities was measured for opposite backazimuths of 120° and 300°, respectively. Such a variation is incompatible with the intrinsic azimuthal anisotropy and the path average approximation made in tomography. I assumed an eastward dipping lithosphere-asthenosphere boundary (LAB) to be the causing structure, inspired by some preliminary velocity models and observations made in previous studies. To test this hypothesis, I carried out 2D full-waveform modeling of the Rayleigh wave propagation. The models include a steep gradient at the LAB in combination with a pronounced reduction in the shear velocity below the LAB. The synthetic results are consistent with the observations: Faster phase velocities are obtained for propagation towards the thinning lithosphere, and lower ones for propagation in the direction of deepening LAB. The interference of reflected surface wave energy at the steep LAB with the forward propagating fundamental mode probably causes this peculiar effect. Second, the joint inversion of Rayleigh surface waves and ambient noise provides structural imaging down to 250 km depth. Resultant from my velocity model, I derive a new crustal model from which maps of the Moho depth as well as of the high-density lower crustal layer (LCL) are obtained. I observe crustal thickening from west to east below the Precambrian low-topography terranes, which is mainly a consequence of eastward thickening of the LCL. In contrast to the southern Scandes, with the overall highest topography (2,500 m), a crustal root below the northern Scandes (max. 2,100 m) is seen which diminish towards the central Scandes (max. 1,000 m). The LAB below the Scandes is deepening from west to east. The sharp steps in the LAB and strong velocity reductions both in the south (90–120 km LAB depth with 5.5% Vsv contrast) and the north (150 km LAB depth with 9% Vsv contrast) surprisingly correlate with the Caledonian mountain front. Whereas smoother laterally varying structures (150–170 km LAB depth with 4% Vsv contrast) are found below the central Scandes. The correlation of the lithosphere thickening with the Caledonian front might be related to metasomatism as result of the orogeny and/or the passive margin rifting. In Precambrian Scandinavia, low-velocity areas below 150 km depth are observed beneath the Archean Karelia craton in northern Finland. At mantle depth, the Paleoproterozoic Norrbotten craton can be separated from the Karelia craton, Caledonides and Paleoproterozic Svecofennian likely due to different degrees of metasomatism. Based on the structural differences, I conclude that different mechanisms are responsible for the compensation of the topography. The northern Scandes are likely compensated by a combined Airy-Pratt isostasy as implied by low-density rocks in the shallow crust (〈15 km depth), a high-density layer in the deep crust (〉10 km LCL thickness) and the mountain root. The strongly reduced velocities at sub-lithospheric depth additionally suggest an uplift contribution from the upper mantle. Since the southern Scandes lacks these crustal attributes, they experience mainly mantle-driven buoyancy. In both cases, however, I assume the influence of small-scale edge-driven convections (EDC) that can arise at sharp LAB gradients. EDC emplaces thereby low-density material at sub-lithospheric depths by the upwelling of hot asthenosphere which implies additional buoyancy of the lithosphere. Moreover, the lateral topography differences along the Scandes can be explained by varying EDC cell dimensions. Primarily, Pratt isostasy compensates the low topography central Scandes, but a contribution from dynamic support could act as well. Ultimately, I see the strong gradients at the LAB below the southern and northern Scandes as the cause of the observed 1θ phase velocity variation. While the smoother velocity structure in the central study area explains the absence of the 1θ effect.

Description: The occurrence and the style of volcanic eruptions are largely controlled by the ways in which magma is stored and transported from the mantle to the surface through the crust. Nevertheless, our understanding of the deep roots of volcano-magmatic systems remains very limited. Here, we use the sources of seismovolcanic tremor to delineate the active part of the magmatic system beneath the Klyuchevskoy Volcanic Group in Kamchatka, Russia. The tremor sources are distributed in a wide spatial region over the whole range of crustal depths connecting different volcanoes of the group. The tremor activity is characterized by rapid vertical and lateral migrations explained by fast pressure transients and dynamic permeability. Our results support the conceptual model of extended and highly dynamic trans-crustal magmatic systems.

Description: Seismic event detection and phase picking are the base of many seismological workflows. In recent years, several publications demonstrated that deep learning approaches significantly outperform classical approaches, achieving human-like performance under certain circumstances. However, as studies differ in the datasets and evaluation tasks, it is unclear how the different approaches compare to each other. Furthermore, there are no systematic studies about model performance in cross-domain scenarios, i.e., when applied to data with different characteristics. Here, we address these questions by conducting a large-scale benchmark. We compare six previously published deep learning models on eight datasets covering local to teleseismic distances and on three tasks: event detection, phase identification and onset time picking. Furthermore, we compare the results to a classical Baer-Kradolfer picker. Overall, we observe the best performance for EQTransformer, GPD and PhaseNet, with a small advantage for EQTransformer on teleseismic data. Furthermore, we conduct a cross-domain study, analyzing model performance on datasets they were not trained on. We show that trained models can be transferred between regions with only mild performance degradation, but models trained on regional data do not transfer well to teleseismic data. As deep learning for detection and picking is a rapidly evolving field, we ensured extensibility of our benchmark by building our code on standardized frameworks and making it openly accessible. This allows model developers to easily evaluate new models or performance on new datasets. Furthermore, we make all trained models available through the SeisBench framework, giving end-users an easy way to apply these models.

Description: The accurate knowledge of the Earth’s orientation and rotation in space is essential for a broad variety of scientific and societal applications. Among others, these include global positioning, near-Earth and deep-space navigation, the realisation of precise reference and time systems as well as studies of geodynamics and global change phenomena. In this paper, we present a refined strategy for processing and combining Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) observations at the normal equation level and formulate recommendations for a consistent processing of the space-geodetic input data. Based on the developed strategy, we determine final and rapid Earth rotation parameter (ERP) solutions with low latency that also serve as the basis for a subsequent prediction of ERPs involving effective angular momentum data. Realising final ERPs on an accuracy level comparable to the final ERP benchmark solutions IERS 14C04 and JPL COMB2018, our strategy allows to enhance the consistency between final, rapid and predicted ERPs in terms of RMS differences by up to 50% compared to existing solutions. The findings of the study thus support the ambitious goals of the Global Geodetic Observing System (GGOS) in providing highly accurate and consistent time series of geodetic parameters for science and applications.

Description: This field campaign aimed at densifying the station coverage on the Armutlu Peninsula in the eastern Sea of Marmara. The Armutlu peninsula is directly crossed by the Armutlu fault, located roughly ~50 km away from the Istanbul metropolitan region. The main objective of this experiment is to characterize the seismic and aseismic deformation of this region. Waveform data are available from the GEOFON data centre, under network code 9P.

Description: This dataset contains subaquatic passive seismic recordings taken in September 2021 at 88 locations off Tuktoyaktuk Island as well as in a small lake (“Lake 3”) between the villages of Tuktoyaktuk and Inuvik, Northwest Territories, Canada. The measurements were part of the “Mackenzie Delta Permafrost Field Campaign” (mCan2021) within the “Modular Observation solutions for Earth Systems” (MOSES) program. Data is from a seismic intermediate-bandwidth seismic sensor lowered for few minutes to the bottom of the sea and lake, respectively, and from underwater short-period sensors deployed for a few days. The aim of the study was to determine the depth of the subaquatic permafrost (local lake and oceanic locations). Raw data is provided in proprietary “Cube” format and standard mseed format.

Description: This data publication contains a seismic survey which was acquired in the Mont Terri Underground Rock Laboratory (URL) in January 2019. The aim of the SI-A experiment (Seismic Imaging Ahead of and around underground infrastructure) is to provide a seismic characterization at the meso scale and to investigate the feasibility of tomographic and reflection imaging in argillaceous environments. The survey covered the different facies types of Opalinus Clay: shaly facies, carbonate -rich sandy facies and sandy facies (Bossart et al. 2017). Three different seismic sources (impact, vibro, ELVIS) were used to acquire the seismic data. The impact and magnetostrictive vibro sources were particularly designed for seismic exploration in the underground (Giese et al. 2005, Richter et al. 2018). The ELVIS source was mainly designed for near-surface investigations on roads or in open terrain (Krawczyk et al. 2012). All data were recorded on 32 3-component geophones (GS-14-L3, 28 Hz) which were deployed in 2 m deep boreholes, fixed at the tip of rock anchors. The data publication covers raw and preprocessed data stored in SEG-Y format.

Description: From June to August 2021, we deployed a dense seismic nodal network across the Hengill geothermal area in southwest Iceland to image and characterize faults and high‐temperature zones at high resolution. The nodal network comprised 498 geophone nodes spread across the northern Nesjavellir and southern Hverahlíð geothermal fields and was complemented by an existing permanent and temporary backbone seismic network of a total of 44 short‐period and broadband stations. In addition, we recorded distributed acoustic sensing data along two fiber optic telecommunication cables near the Nesjavellir geothermal power plant with commercial interrogators. During the time of deployment, a vibroseis survey took place around the Nesjavellir power plant. Here, we describe the network and the recorded datasets. Furthermore, we show some initial results that indicate a high data quality and highlight the potential of the seismic records for various follow up studies, such as high‐resolution event location to delineate faults and body‐ and surface‐wave tomographies to image the subsurface velocity structure in great detail.

Description: BACKGROUND AND OBJECTIVES: Soil or rock types in a region are often interpreted qualitatively by visually comparing various geophysical properties such as seismic wave velocity and vulnerability, as well as gravity data. Better insight and less human-dependent interpretation of soil types can be obtained from a joint analysis of separated and independent geophysical parameters. This paper discusses the application of a neural network approach to derive rock properties and seismic vulnerability from horizontal-to-vertical seismic ratio and seismic wave velocity data recorded in Majalengka-West Java, Indonesia.METHODS: Seismic microtremors were recorded at 54 locations and additionally multichannel analyses of surface wave experiments were performed at 18 locations because the multichannel analyses of surface wave experiment needs more effort and space. From the two methods, the values of the average shear wave velocity for the upper 30 meters, peak amplitudes and the dominant frequency between the measurement points were obtained from the interpolation of those geophysical data. Neural network was then applied to adaptively cluster and map the geophysical parameters. Four learning model clusters were developed from the three input seismic parameters: shear wave velocity, peak amplitude, and dominant frequency. FINDINGS: Generally, the values of the horizontal to vertical spectral ratios in the west of the study area were low (less than 5) compared with those in the southeastern part. The dominant frequency values in the west were mostly low at around 0.1–3 Hertz, associated with thick sedimentary layer. The pattern of the shear wave velocity map correlates with that of the horizontal to vertical spectral ratio map as the amplification is related to the soil or rock rigidity represented by the shear wave velocity. The combination of the geophysical data showed new features which is not found on the geological map such as in the eastern part of the study area. CONCLUSION: The application of the neural network based clustering analysis to the geophysical data revealed four rock types which are difficult to observe visually. The four clusters classified based on the variation of the geophysical parameters show a good correlation to rock types obtained from previous geological surveys. The clustering classified safe and vulnerable regions although detailed investigation is still required for confirmation before further development. This study demonstrates that low-cost geophysical experiments combined with neural network-based clustering can provide additional information which is important for seismic hazard mitigation in densely populated areas.

Description: The Walvis Ridge (WR) is the most prominent hotspot track related to the opening in the South Atlantic Ocean. Several hypotheses have been developed to explain its origin and evolution. The presence of a massive magmatic structure at the landfall of the WR in Northwest Namibia raised speculation about the role of a hotspot during the opening of the South Atlantic ocean. To investigate its deeper velocity structure at the junction of the WR with the African continent was the focus of the amphibious seismological WALPASS experiment. In total 12 ocean-bottom seismometers and 28 broad-band land stations were installed between 2010 and 2012 to acquire seismological data. Here, we present the results of seismic ambient noise tomography to investigate to which extent the Tristan hotspot modified the crustal structure in the landward prolongation of the ridge and in the adjacent oceanic basins. For the tomography, vertical and hydrophone component cross correlations for 〉300 d for OBS stations and between 1 and 2 yr for land stations data were analysed. More than 49 000 velocity measurements (742 dispersion curves) were inverted for group velocity maps at 75 individual signal periods, which then had been inverted for a regional 3-D shear wave velocity model. The resulting 3-D model reveals structural features of the crust related to the continent–ocean transition and its disturbance caused by the initial formation of the WR ∼130 Ma. We found relatively thick continental crust below Northwest Namibia and below the near-shore part of the WR, a strong asymmetry offshore with typical, thin oceanic crust in the Namibe Basin (crossing over into the Angola Basin further offshore) to the North and a wide zone of transitional crust towards the Walvis Basin south of the WR.

Description: Earthquakes and slow-slip events interact, however, detailed studies investigating their interplay are still limited. We generate the highest resolution microseismicity catalog to date for the northern Armutlu Peninsula in a ∼1-year period to perform a detailed seismicity distribution analysis and correlate the results with a local, geodetically observed slow-slip transient within the same period. Seismicity shows a transition of cluster-type behavior from swarm-like to burst-like, accompanied by an increasing relative proportion of clustered (non-Poissonian) relative to background (Poissonian) seismicity and gradually decreasing b-value as the geodetically observed slow-slip transient ends. The observed slow-slip transient decay correlates with gradually increasing effective-stress-drop values. The observed correlation between the b-value and geodetic transient highlights the influence of aseismic deformation on seismic deformation and the impact of slow-slip transients on local seismic hazard.

Description: The identification of the chemical status of groundwater is a prerequisite for the sustainable management and development of groundwater resources. A better assessment of the chemical status of the groundwater requires the knowledge and understanding of the natural background concentrations to establish threshold values of chemical pollutants in groundwater. The aim of this study is to estimate the natural background levels, the threshold value (TV) of nitrate-nitrogen (NO3--N) and to identify its source in the groundwater in the Bono, Ahafo and Bono East regions of Ghana. A total of 165 groundwater samples were taken from the crystalline and sedimentary aquifers in the study area. Iterative outlier removal technique and a Gaussian mixture model were then used to assess the natural background and threshold nitrate-nitrogen concentrations in the groundwater. Chloride data was then used to trace the NO3-–N source in the groundwater. The estimated NBL of –NO3-–N in the area ranges from [0.001–3.9] mg/L with an expected value of 1.25 mg/L and calculated TV of 6.95 mg/L. The data suggest that NO3-–N concentrations are homogeneous across all the lithologies underlying the study area. The results showed that agricultural, domestic, and denitrification contribute significantly to the loading of NO3-–N concentration in the groundwater. The estimated threshold range of NO3-–N provides the baseline nitrate-nitrogen concentration for future studies in the region. However, the results are inconclusive, and we recommend using isotopic detection (15N-NO3- and 18O- NO3-) in future studies through comprehensive and sustainable regional monitoring of the aquifer system in order to further limit the source of nitrate-nitrogen in the groundwater system.

Description: Ruptures of the largest earthquakes can last between a few seconds and several minutes. An early assessment of the final earthquake size is essential for early warning systems. However, it is still unclear when in the rupture history this final size can be predicted. Here we introduce a probabilistic view of rupture evolution - how likely is the event to become large - allowing for a clear and well-founded answer with implications for earthquake physics and early warning. We apply our approach to real time magnitude estimation based on either moment rate functions or broadband teleseismic P arrivals. In both cases, we find strong and principled evidence against early rupture predictability because differentiation between differently sized ruptures only occurs once half of the rupture has been observed. Even then, it is impossible to foresee future asperities. Our results hint toward a universal initiation behavior for small and large ruptures.

Description: An earthquake swarm affected the Bransfield Strait, Antarctica, a unique rift basin in transition from intra-arc rifting to ocean spreading. The swarm, counting ~85,000 volcano-tectonic earthquakes since August 2020, is located close to the Orca submarine volcano, previously considered inactive. Simultaneously, geodetic data reported up to ~11 cm northwestward displacement over King George Island. We use a broad variety of geophysical data and methods to reveal the complex migration of seismicity, accompanying the intrusion of 0.26–0.56 km3 of magma. Strike-slip earthquakes mark the intrusion at depth, while shallower normal faulting the ~20 km long lateral growth of a dike. Seismicity abruptly decreased after a Mw 6.0 earthquake, suggesting the magmatic dike lost pressure with the slipping of a large fault. A seafloor eruption is likely, but not confirmed by sea surface temperature anomalies. The unrest documents episodic magmatic intrusion in the Bransfield Strait, providing unique insights into active continental rifting.

Description: On 12 August 2021, a 〉220 s lasting complex earthquake with Mw 〉 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 Mw 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 Mw 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 Mw 7.6. The aftershock distribution confirms the extent and curvature of the rupture. Some mechanisms are consistent with the mainshocks, but many indicate also activation of secondary faults. Rupture velocities and radiated frequencies varied strongly between different stages of the rupture, which might explain the variability of published source parameters.

Description: Strong anisotropy of seismic velocity in the Earth's crust poses serious challenges for seismic imaging. Where in situ seismic properties are not available, the anisotropy can be determined from velocity analysis of surface and borehole seismic profiles. This is well established for dense, long-offset reflection seismic data. However, it is unknown how applicable this approach is for sparse seismic reflection data with low fold and short offsets in anisotropic metamorphic rocks. Here, we show that anisotropy parameters can be determined from a sparse 3-D data set at the COSC-1 borehole site in the Swedish Caledonides and that the results agree well with the seismic anisotropy parameters determined from seismic laboratory measurements on core samples. Applying these anisotropy parameters during 3-D seismic imaging improves the seismic image of the high-amplitude reflections especially in the vicinity of the lower part of the borehole. Strong reflections in the resulting seismic data show good correlation with the borehole-derived lithology. Our results aid the interpretation and extrapolation of the seismic stratigraphy of the Lower Seve Nappe in Jämtland and other parts in the Caledonides.

Description: This dataset provides friction data from ring-shear tests on glass beads with a diameter of 200-300 µm used in analogue modelling of tectonic processes as a rock analogue for “weak” layers in the earth’s upper crust (e.g. Klinkmüller et al., 2016; Ritter et al., 2016; Lohrmann et al., 2003) or as “seismogenic” crust (Rudolf et al., 2022). The glass beads are characterized by means of internal friction coefficients µ and cohesion C. According to our analysis the materials show a Mohr-Coulomb behaviour characterized by a linear failure envelope. Peak, dynamic and reactivation friction coefficients of the glass beads are µP = 0.51 , µD = 0.40, and µR = 0.44, respectively (Table 5). Cohesion of the material ranges between 40 Pa and 70 Pa. The material shows a minor rate-weakening of ~1% per ten-fold change in shear velocity v and a stick-slip behaviour at low shear velocities and at high loads.

Description: This dataset provides friction data from ring-shear tests on glass beads with a diameter of 100-200 µm used in analogue modelling of tectonic processes as a rock analogue for “weak” layers in the earth’s upper crust (e.g. Klinkmüller et al., 2016; Ritter et al., 2016; Lohrmann et al., 2003) or as “seismogenic” crust (Rudolf et al., 2022). The glass beads are characterized by means of internal friction coefficients µ and cohesion C. According to our analysis the materials show a Mohr-Coulomb behaviour characterized by a linear failure envelope. Peak, dynamic and reactivation friction coefficients of the glass beads are µP = 0.50 , µD = 0.39, and µR = 0.46, respectively (Table 5). Cohesion of the material is close to zero Pa. The material shows a minor rate-weakening of ~1% per ten-fold change in shear velocity v and a stick-slip behaviour at low shear velocities and at high loads.

Description: Coalbed deposits are a unique subsurface environment and represent an underutilized resource for methane generation. Microbial communities extant in coalbed deposits are responsible for key subsurface biogeochemical cycling and could be utilized to enhance methane production in areas where existing gas wells have depleted methane stores, or in coalbeds that are unmined, or conversely be utilized for mitigation of methane release. Here we utilize metagenomics and metagenome-assembled genomes (MAGs) to identify extant microbial lineages and genome-resolved microbial metabolisms of coalbed produced water, which has not yet been explored in the Appalachian Basin (AppB). Our analyses resulted in the recovery of over 40 MAGs from 8 coalbed methane wells. The most commonly identified taxa among samples were hydrogenotrophic methanogens from the order Methanomicrobiales and these dominant MAGs were highly similar to one another. Conversely, low-abundance coalbed bacterial populations were taxonomically and functionally diverse, mostly belonging to a variety of Proteobacteria classes, and encoding various hydrocarbon solubilization and degradation pathways. The data presented herein provides novel insights into AppB coalbed microbial ecology, and our findings provide new perspectives on underrepresented Methanocalculus species and low-relative abundance bacterial assemblages in coalbed environments, and their potential roles in stimulation or mitigation of methane release.

Description: This dataset provides friction data from ring-shear tests on glass beads with a diameter of less than 50 µm used in analogue modelling of tectonic processes as a rock analogue for “weak” layers in the earth’s upper crust (e.g. Klinkmüller et al., 2016; Ritter et al., 2016; Lohrmann et al., 2003) or as “seismogenic” crust (Rudolf et al., 2022). The glass beads are characterized by means of internal friction coefficients µ and cohesion C. According to our analysis the materials show a Mohr-Coulomb behaviour characterized by a linear failure envelope. Peak, dynamic and reactivation friction coefficients of the glass beads are µP = 0.47 , µD = 0.44, and µR = 0.47, respectively (Table 5). Cohesion of the material ranges between 50 Pa and 70 Pa. The material shows a neglectable rate-weakening of 〈1% per ten-fold change in shear velocity v.

Description: The influence of elevated temperature on injection-induced fault slip is poorly constrained. In this study, at steady-state elevated temperatures, triaxial shear-flow experiments on a sawcut fault in granite were conducted to simulate injection-induced slip of a critically stressed fault. Our results suggest that an elevated temperature favors a more uniform fluid pressure distribution over the fault surface mainly by reducing water viscosity. At temperatures above ambient, a larger perturbation force from the injected fluid is required to reactivate the fault primarily because of the enhanced thermally activated fault healing processes, resulting in a faster fault slip rate upon failure. This study may partially explain the causal link between higher reservoir temperature and higher maximum magnitude of injection-induced earthquakes in geothermal systems, and the observation that larger magnitude seismic events concentrate near the deeper part of the reservoir, where temperature is higher.

Description: Land use/land cover change is an important carrier for the study of human-land relationship. Yuxi City is a typical area of with alternating mountain and basin landforms, forming a special human-land system with “mountains” and “basins” as the core elements. Taking 75 towns in Yuxi City, Yunnan Province as a case study, this paper uses a comprehensive evaluation model of land use/land cover change and related analysis methods to analyze the changes of land use pattern in mountainous areas and basin areas respectively from 1995 to 2018, and to reveal their spatial differences and its influencing factors. The results show that: 1) The dynamic evolution of land use in the mountainous area and the basin area presented obvious stage characteristics. From 1995 to 2005, the average comprehensive dynamic degree of land use in the mountainous area was 1.7861, which was significantly higher than the 1.7033 in the basin area. The average comprehensive dynamic degree of land use in mountainous areas from 2005 to 2018 was 1.1284, which was significantly lower than 1.9427 in the basin area. 2) From 1995 to 2018, the land use degree and the comprehensive dynamic degree of land use continued to rise in the basin area, while the mountainous area showed a trend of rising first and then falling. The overall change trend of land use depletion in the mountainous area was consistent with that in the basin area, but the mountainous area was always higher than that in the basin area. 3) The land use change in mountainous areas and basin areas was mainly reflected in the difference of natural factors and socio-economic fators. The radiation and agglomeration functions of the basin area have always attracted people to migrate from the mountains to the basin, which was beneficial to the ecological restoration of the vegetation in the mountains. Since the mountainous area and the basin area are geographically adjacent, the coupling and coordination of the two is the premise and foundation for the sustainable development of the region. This causal relationship of land use changes provides a reliable basis for the regulation of mountain-basin human-land coupling relationship.