Centroid moment tensor inversions of offshore earthquakes using a three-dimensional velocity structure model: Slip distributions on the plate boundary along the Nankai Trough

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1093/gji/ggaa238.

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Authors

Shunsuke Takemura , Ryo Okuwaki , Tatsuya Kubota , Katsuhiko Shiomi, Takeshi Kimura, Akemi Noda

Abstract

Due to complex three-dimensional (3D) heterogeneous structures, conventional one-dimensional (1D) analysis techniques using onshore seismograms can yield incorrect estimation of earthquake source parameters, especially dip angles and centroid depths of offshore earthquakes. Combining long-term onshore seismic observations and numerical simulations of seismic wave propagation in a 3D model, we conducted centroid moment tensor (CMT) inversions of earthquakes along the Nankai Trough between April 2004 and August 2019 to evaluate decade-scale seismicity. Green’s functions for CMT inversions of earthquakes with moment magnitudes of 4.3–6.5 were evaluated using finite-difference method simulations of seismic wave propagation in the regional 3D velocity structure model. Significant differences of focal mechanisms and centroid depths between previous 1D and our 3D catalogues were found in the solutions of offshore earthquakes. By introducing the 3D structures of the low-velocity accretionary prism and the Philippine Sea Plate, dip angles and centroid depths for offshore earthquakes were well-constrained. Teleseismic CMT also provides robust solutions but our regional 3D CMT could provide better constraints of dip angles. Our 3D CMT catalogue and published slow earthquake catalogues depicted spatial distributions of slip behaviours on the plate boundary along the Nankai Trough. The regular and slow interplate earthquakes were separately distributed, with these distributions reflecting the heterogeneous distribution of effective strengths along the Nankai Trough plate boundary. By comparing the spatial distribution of seismic slip on the plate boundary with the slip-deficit rate distribution, regions with strong coupling were clearly identified.

DOI

https://doi.org/10.31223/osf.io/nbd79

Subjects

Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics, Planetary Sciences

Keywords

Nankai Trough, Centroid moment tensor inversion, finite-difference method, heterogeneous structure, Seismicity

Dates

Published: 2019-11-20 16:20

Last Updated: 2020-05-15 14:40

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License

Academic Free License (AFL) 3.0

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