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  • 2020-2022  (15)
  • 1
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    Forming a Mogi Doughnut in the Years Prior to and Immediately Before the 2014 M 8.1 Iquique, Northern Chile, Earthquake (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-08-21
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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    PAPER CURRENT
  • 2
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    Linear Relationship Between Aftershock Productivity and Seismic Coupling in the Northern Chile Subduction Zone (2021)
    Details
    Publication Date: 2021-09-24
    Description: The aftershock productivity is known to strongly vary for different mainshocks of the same magnitude, which cannot be simply explained by random fluctuations. In addition to variable source mechanisms, different rheological properties might be responsible for the observed variations. Here we show, for the subduction zone of northern Chile, that the aftershock productivity is linearly related to the degree of mechanical coupling along the subduction interface. Using the earthquake catalog of Sippl et al. (2018, https://doi.org/10.1002/2017JB015384), which consists of more than 100,000 events between 2007 and 2014, and three different coupling maps inferred from interseismic geodetic deformation data, we show that the observed aftershock numbers are significantly lower than expected from the Båth's law. Furthermore, the productivity decays systematically with depth in the uppermost 80 km, while the b value increases. We show that this lack of aftershocks and the observed depth dependence can be simply explained by a linear relationship between the productivity and the coupling coefficient, leading to Båth law only in the case of full coupling. Our results indicate that coupling maps might be useful to forecast aftershock productivity and vice versa.
    Keywords: seismic coupling ; aftershocks ; earthquake triggering
    Language: English
    Type: map
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    CITATION GEO-LEO
  • 3
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    DeepPhasePick: A method for detecting and picking seismic phases from local earthquakes based on highly optimized convolutional and recurrent deep neural networks (2021)
    In:  Geophysical Journal International
    Details
    Publication Date: 2021-11-01
    Description: Seismic phase detection, identification and first-onset picking are basic but essential routines to analyse earthquake data. As both the number of seismic stations, globally and regionally, and the number of experiments greatly increase due to ever greater availability of instrumentation, automated data processing becomes more and more essential. For example for modern seismic experiments involving 100s to even 1000s instruments, conventional human analyst-based identification and picking of seismic phases is becoming unfeasible, and the introduction of automatic algorithms mandatory. In this paper, we introduce DeepPhasePick, an automatic two-stage method that detects and picks P and S seismic phases from local earthquakes. The method is entirely based on highly optimized deep neural networks, consisting of a first stage that detects the phases using a convolutional neural network, and a second stage that uses two recurrent neural networks to pick both phases. Detection is performed on three-component seismograms. P- and S-picking is then conducted on the vertical and the two-horizontal components, respectively. Systematic hyperparameter optimization was applied to select the best model architectures and to define both the filter applied to pre-process the seismic data as well as the characteristics of the window sample used to feed the models. We trained DeepPhasePick using seismic records extracted from two sets of manually picked event waveforms originating from northern Chile (∼39 000 records for detection and ∼36 000 records for picking). In different tectonic regimes, DeepPhasePick demonstrated the ability to both detect P and S phases from local earthquakes with high accuracy, as well as predict P- and S-phase time onsets with an analyst level of precision. DeepPhasePick additionally computes onset uncertainties based on the Monte Carlo Dropout technique as an approximation of Bayesian inference. This information can then further feed an associator algorithm in an earthquake location procedure.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 4
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    Trajectory models for daily displacement time series in the five years preceding the 2010 Maule Mw 8.8, Chile, and 2011 Tohoku-oki Mw 9.0, Japan earthquakes (2020)
    GFZ Data Services
    Details
    Publication Date: 2020-05-11
    Description: This supplement contains GNSS displacement time series, fluid loading displacement time series predictions, and trajectory models for these time series. The time series are for the study regions of the paper: "Months-Long thousand-km-scale wobbling before great subduction earthquakes". These study regions are (1) Japan and surrounding countries and (2) Chile and surrounding countries. Network solution daily GNSS time series displacements in Chile and surrounding countries in the South American network have been produced by GFZ. Network solution daily GNSS time series of displacements in Japan have been produced by the Geospatial Information Authority of Japan (GSI). PPP daily GNSS time series of displacements in Japan and surrounding countries have been produced by the Nevada Geodetic Laboratory, Nevada Bureau of Mines and Geology, University of Nevada, Reno. Fluid loading predictions have been made using the HYDL, NTOL, NTAL, and SLEL products of the ESMGFZ. Readme ascii files in this data supplement contain instructions on how the data are ordered. Furthermore, the Readme file contains the relevant references and acknowledgments for readers who want to use these data in their own published studies.
    Language: English
    Type: info:eu-repo/semantics/workingPaper
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  • 5
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    Tajik Basin and Southwestern Tian Shan, Northwestern India‐Asia Collision Zone: 2. Timing of Basin Inversion, Tian Shan Mountain Building, and Relation to Pamir‐Plateau Advance and Deep India‐Asia Indentation (2020)
    In:  Tectonics
    Details
    Publication Date: 2020-12-11
    Description: The Tajik basin and southwestern Tian Shan constitute the northwestern tip of the India‐Asia collision zone. Basin inversion formed the thin‐skinned Tajik fold‐thrust belt, outlined by westward convex fold trains, underlain by a décollement in Jurassic evaporites. The belt's leading edge—the Uzbek Gissar—and its transpressional northern lateral margin—the Tajik Gissar—constitute the thick‐skinned foreland buttresses. Apatite fission‐track data indicate ~40‐ to 15‐Ma reheating by sediment burial in the Tian Shan. In the Gissar and the Tajik fold‐thrust belt, apatite fission‐track and (U,Th)/He ages date the major phase of shortening/erosion between ~12 and 1 Ma, with exhumation to 2‐ to 3‐km crustal depths within a few Myr after onset of shortening. Shortening spread immediately across the fold‐thrust belt, typical for belts floored by a detachment in ductile rocks, and into the foreland buttresses. Reactivation concentrated in the internal (eastern) fold‐thrust belt with the thickest evaporates. The youngest ages (~6.6–1.6 Ma) occur along the Vakhsh thrust, the active erosional front of the fold‐thrust belt in the northeastern Tajik basin, where it narrows between the converging Tian Shan and Pamir. Our study links major events in the Pamir hinterland with the Tajik basin and Tian Shan foreland. In the late Eocene–early Miocene, the advancing Pamir‐plateau crust loaded the foreland, inducing subsidence, reheating, and early shortening. Basin inversion and major shortening/transpression in the foreland buttresses from ~12 Ma onward were synchronous with the subcrustal indentation of Indian lithosphere into the Tajik‐Tarim basin lithosphere and the onset of its rollback beneath the Pamir.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 6
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    CaTeNA – Climatic and Tectonic Natural Hazards in Central Asia Final virtual workshop September 24-25 2020 (2020)
    GFZ German Research Centre for Geosciences
    Details
    Publication Date: 2020-11-18
    Description: CaTeNA – Climatic and Tectonic Natural Hazards in Central Asia – is an interdisciplinary, international project funded by the German Ministry of Education and Research to study natural hazards in Central Asia. Central Asia is one of the most tectonically active regions of the world and is influenced by both the west wind zone and monsoon. CaTeNA is examining the two most serious natural hazards arising from these conditions: Earthquakes and mass movements. The project goal is to better understand the underlying processes and triggering factors and to better estimate the resulting risks. For this purpose, CaTeNA localises tectonic faults and determines deformation rates and their changes. Focus is put on two of the most active fault systems, the Main Pamir Thrust and the Darvaz Fault crossing Tajikistan and Kyrgyzstan. We try to estimate recurrence intervals of large earthquakes and to understand their relationship to mass movements using paleo-seismology, geomorphology and remote sensing. The current deformation field is characterised and quantified using the methods of space geodesy and seismology. The results will be incorporated into the openly accessible Central Asian Tectonic Database developed within the project, making it accessible to the public, stakeholders and decision-makers. They form the basis for a more accurate estimation of the risk for earthquakes and landslides. Another important project goal is the development and implementation of a dynamic risk assessment for landslides, including high-resolution, model-based precipitation and snowmelt maps. This allows for an improved estimation of the effects of geological hazards on inhabited areas and traffic infrastructure. Direct and efficient risk communication is achieved through interactive visualisation based on a dynamic multilingual web GIS platform. This is an essential step on the path to an early-warning system that takes into account the most important triggering factors. This data repository provides pdf files and recorded videos of talks presented during the final online workshop of the project.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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    Format: application/vnd.openxmlformats-officedocument.presentationml.slideshow
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  • 7
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    Tajik Basin and Southwestern Tian Shan, Northwestern India‐Asia Collision Zone: 1. Structure, Kinematics, and Salt Tectonics in the Tajik Fold‐and‐Thrust Belt of the Western Foreland of the Pamir (2020)
    In:  Tectonics
    Details
    Publication Date: 2020-12-11
    Description: Surface, seismic, and borehole data characterize the Neogene‐Recent Tajik fold‐and‐thrust belt of the Tajik basin. The basin experienced little sub‐detachment basement deformation, acting as a rigid foreland plate during the Pamir orogeny. The Tajik fold‐and‐thrust belt contains variable thin‐skinned structural styles, changing along and across strike as a function of the thickness and facies of Upper Jurassic evaporites, which constitute the basal detachment, and the influence of the surrounding thick‐skinned belts. The southern Tajik fold‐and‐thrust belt shows regularly spaced, salt‐cored, thrusted detachment anticlines that transition northward into imbricated thrust sheets grouped in oppositely verging stacks facing each other across a common footwall syncline. The width of the fold‐and‐thrust belt decreases northeastward accommodated by the Ilyak fault, a lateral ramp developed over a seismically active dextral basement fault. The southeastern Tajik fold‐and‐thrust belt contains massive subaerial salt sheets, formed by squeezing of preexisting salt diapirs. The salt‐tectonic domain originates from a local depocenter within the Late Jurassic Amu Darya‐Tajik evaporitic basin. Serial cross sections, integrating the structural geometries, yielded minimum thin‐skinned shortening oriented at ~90° to the India‐Asia convergence direction, increasing from ~93 km in the south to ~148 km in the center, and dropping to ~22 km in the northeast; total shortening—including the foreland buttress—is ≥170 km. Most of the shortening in the central‐southern Tajik fold‐and‐thrust belt occurred by hinterland‐vergent, high‐displacement back thrusts. The Pamir played a dominant role in the transfer of shortening to the sedimentary infill of the Tajik basin with the Tian Shan acting as a semi‐passive buttress.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 8
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    Lithospheric delamination beneath the southern Puna plateau resolved by local earthquake tomography (2020)
    In:  Journal of Geophysical Research: Solid Earth
    Details
    Publication Date: 2021-02-04
    Description: We present a local earthquake tomography to illuminate the crustal and uppermost mantle structure beneath the southern Puna plateau and to test the delamination hypothesis. Vp and Vp/Vs ratios were obtained using travel time variations recorded by 75 temporary seismic stations between 2007 and 2009. In the upper crust, prominent low Vp anomalies are found beneath the main volcanic centers, indicating the presence of magma and melt beneath the southern Puna plateau. Beneath the Moho at around 90 km depth, a strong high Vp anomaly is detected just west of the giant backarc Cerro Galan Ignimbrite caldera. This high Vp anomaly is only resolved if earthquakes with an azimuthal gap up to 300° are included in the inversion. However, we show through data‐subset and synthetic tests that the anomaly is robust due to our specific station‐event geometry and interpret it as a delaminated block of lower crust and uppermost mantle lithosphere under the southern Puna plateau. The low velocities in the crust are interpreted as a product of the delamination event that triggered the rise of fluids and melts into the crust and induced the high topography in this part of the plateau. The tomography also reveals the existence of low velocity anomalies that link arc magmatism at the Ojos del Salado volcanic center with slab seismicity clusters at depths of about 100 and 150 km and support fluid transport in the mantle wedge due to dehydration reaction within the subducted slab.
    Type: info:eu-repo/semantics/article
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  • 9
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    Pre-seismic earthquake catalog, inter-seismic locking model, and corrected gravity field for the 2014 M8.1 Iquique, northern Chile, earthquake rupture region (2020)
    GFZ Data Services
    Details
    Publication Date: 2020-08-19
    Description: These data sets accompany the article "Forming a Mogi Doughnut in the years prior to and immediately before the 2014 M8.1 Iquique, Northern Chile earthquake" (Schurr et al., 2020). The data sets consist of an earthquake catalog (2020-011_schurr-et-al_mogi_eqk_cat.txt) preceding the 2014 M8.1 Iquique, northern Chile earthquake, an inter-seismic locking model derived from GPS data for the northern Chile subduction zone (as plain text table and Generic Mapping Tools [GMT, Wessel et al. 2019] grid file: 2020-011_schurr-et-al_mogi_locking.txt and .grd) and the gravity field corrected for water column and subducted slab of the source region (GMT grid file: 2020-011_schurr-et-al_mogi_gravity). All data files are combined in one zip folder.
    Language: English
    Type: info:eu-repo/semantics/workingPaper
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  • 10
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    Local Earthquake Tomographic Models of the Southern Puna Plateau (2020)
    GFZ Data Services
    Details
    Publication Date: 2020-10-27
    Description: This data publication includes digital data of the final 3D tomographic model from Chen et al. (2020: Lithospheric delamination beneath the southern Puna plateau resolved by local earthquake tomography). The 3D seismic velocity models are results of a local earthquake tomography which is performed to illuminate the crustal and uppermost mantle structure beneath the southern Puna plateau and to test the delamination hypothesis. The Southern Puna is distinctive from the rest of the Central Andean plateau in having a higher topographic elevation, a thinner lithosphere and in being flanked to the south by the Chilean flat slab region. Previous investigations involving geochemical, geological and geophysical observations, have invoked lithospheric delamination to explain the distinctive magmatic and structural history, elevation and lithospheric thickness of the region. In the present study, Vp and Vp/Vs ratios were obtained using travel time variations recorded by 75 temporary seismic stations between 2007 and 2009. The earthquakes catalog (Mulcahy et al., 2014) contains 1903 local earthquakes (25077 P- and 14059 S-picks). A minimum 1D model is derived with software VELEST (Kissling et al., 1995). The 3D tomographic inversion is performed with software SIMULPS (Thurber, 1983; Evans et al., 1994). Spread values are used to define well resolved model domains (6 for Vp and 5.5 for Vp/Vs), which are calculated from the model resolution matrix (Toomey & Foulger, 1989). The data are provided as one tar.gz archive. Individual ASCII files contain, at each depth from 0 to 200 km: - Vp model (model.vp.depth_???km), format: longitude, latitude, depth, Vp perturbation, absolute Vp - Vp/Vs model (model.vpvs.depth_???km), format: longitude, latitude, depth, Vp/Vs perturbation, absolute Vp/Vs - spread values for Vp (spread.vp.depth_???km), format: longitude, latitude, depth, spread value - spread values for Vp/Vs model (spread.vpvs.depth_???km), format: longitude, latitude, depth, spread value
    Language: English
    Type: info:eu-repo/semantics/workingPaper
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