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Impact of the offshore seismograph network and 3-D seismic velocity structure model on centroid moment tensor analysis for offshore earthquakes: Application to the Japan Trench subduction zone
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  • Lina Yamaya,
  • Hisahiko Kubo,
  • Katsuhiko Shiomi,
  • Shunsuke Takemura
Lina Yamaya
National Research Institute for Earth Science and Disaster Resilience

Corresponding Author:[email protected]

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Hisahiko Kubo
National Research Institute for Earth Science and Disaster Resilience
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Katsuhiko Shiomi
National Research Institute for Earth Science and Disaster Resilience
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Shunsuke Takemura
Earthquake Research Institute, the University of Tokyo
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Abstract

Recently, a widespread and densely continuous-recording ocean-bottom seismograph network has been deployed in the Japan Trench subduction zone. Utilizing the offshore network data improves azimuthal station coverage for offshore earthquakes in the Japan Trench subduction zone. It has a potential to obtain centroid moment tensor (CMT) solutions more accurately than conventional analyses using onshore networks and a simple one-dimensional seismic velocity structure model. In this study, we conducted CMT inversion for subduction zone earthquakes that occurred between April 1, 2017, and March 31, 2024, with a moment magnitude range of 5.2–7.0. We used seismograms obtained from both the offshore and onshore networks. We calculated Green’s functions using a three-dimensional seismic velocity structure model. Our CMT solutions with thrust-type mechanisms mostly indicated depths and dip angles consistent with the plate interface. For earthquakes in the outer-rise region, our CMT solutions were characterized as normal-fault mechanisms. The joint use of the offshore and onshore networks reduced the estimation errors of the CMT solutions compared with the only use of the onshore network, although the optimal solutions were consistent. The dip angles for the thrust earthquakes determined by our analysis were more consistent with the dip angle of the plate boundary than those determined by conventional CMT analyses. Additionally, we found that the conventional CMT analysis could introduce a systematic bias in depth and magnitude determinations. This finding highlights the importance of an offshore seismograph network and a reliable seismic velocity structure model for CMT inversions.
23 Jul 2024Submitted to ESS Open Archive
25 Jul 2024Published in ESS Open Archive