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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 119 (1994), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Following the Chalfant Valley earthquake of 1986 July 21 (ML= 6.4), the USGS deployed 120 vertical-component seismometers to obtain dense array recordings of aftershocks. From this data set, we selected three events with the best station coverage to obtain acoustic images of the earthquake sources. the events were relocated using a layered velocity model and models with a constant velocity and a constant gradient, to obtain minimum traveltime residuals. All models performed similarly well. Preprocessing of the data prior to the extrapolation consisted of applying static corrections, lowpass filtering and spatial interpolation as well as spatial tapering at the edges of the recording line. For the back projection of the recorded wavefield, we used a second-order finite-difference reverse-time extrapolation technique similar to McMechan (1982). While for two events, no focusing of the energy could be obtained, an acoustic image of one earthquake source was retrieved. In order to obtain a better understanding of the physical meaning of acoustic imaging, we applied the same processing and extrapolation scheme to synthetic seismograms calculated using the reflectivity method. For the present data set these tests indicate that the influence of the 1-D velocity model on the focusing quality is very low. the most severe limitations, however, are due to the finite aperture and gaps of the recording line. the spatial sampling of the wavefield limits the frequency range used for extrapolation, so that the resolution is beyond the scale of the source processes. the finite aperture leads to polarity reversals in the final source image, which makes an interpretation of the radiation pattern at the time of focusing from the reconstructed image impossible.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2022-02-11
    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, that is, 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 data sets 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 data sets 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 data sets. Furthermore, we make all trained models available through the SeisBench framework, giving end-users an easy way to apply these models.
    Description: This work was supported by the Helmholtz Association Initiative and Networking Fund on the HAICORE@KIT partition. J. Münchmeyer acknowledges the support of the Helmholtz Einstein International Berlin Research School in Data Science (HEIBRiDS). The authors thank the Impuls-und Vernetzungsfonds of the HGF to support the REPORT-DL project under the grant agreement ZT-I-PF-5-53. This work was also partially supported by the project INGV Pianeta Dinamico 2021 Tema 8 SOME (CUP D53J1900017001) funded by Italian Ministry of University and Research “Fondo finalizzato al rilancio degli investimenti delle amministrazioni centrali dello Stato e allo sviluppo del Paese, legge 145/2018.” Open access funding enabled and organized by Projekt DEAL.
    Description: Published
    Description: e2021JB023499
    Description: 3T. Fisica dei terremoti e Sorgente Sismica
    Description: JCR Journal
    Keywords: seismic phase recognition ; deep learnig ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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