[SCG58-P01] CMT inversion of offshore earthquakes along the Nankai Trough: Separated distributions of slow and regular earthquakes on the plate boundary
Keywords:Nankai Trough, CMT inversion, offshore earthquake, 3D heterogeneous structure
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. Green’s functions for CMT inversions of moderate earthquakes were evaluated via OpenSWPC (Maeda et al., 2017) using the Japan Integrated Velocity Structure Model (Koketsu et al., 2012). We re-analyzed moderate (Mw 4.3-6.5) earthquakes listed in the F-net catalog (Fukuyama et al., 1998; Kubo et al., 2002) that occurred from April 2004 to August 2019. By introducing the 3D structures of the low-velocity accretionary prism and the Philippine Sea Plate, our CMT inversion method provided better constraints of dip angles and centroid depths for offshore earthquakes. These two parameters are important for evaluating earthquake types in subduction zones.
Our 3D CMT catalog of offshore earthquakes and published slow earthquake catalogs (e.g., Kano et al., 2018) along the Nankai Trough depicted spatial distributions of slip behaviors on the plate boundary. The regular and slow interplate earthquakes were separately distributed, with these distributions reflecting the heterogeneous distribution of effective strengths on the plate boundary. By comparing the spatial distribution of seismic slip on the plate boundary with the slip-deficit rate distribution (Noda et al., 2018), regions with strong coupling were identified.
We used F-net waveform data and the F-net MT catalog (https://doi.org/10.17598/NIED.0005). Our CMT catalog and CMT results of assumed source grids for each earthquake are available from https://doi.org/10.5281/zenodo.3661116. The FDM simulations of seismic wave propagation were conducted on the computer system of the Earthquake and Volcano Information Center at the Earthquake Research Institute, the University of Tokyo. This study was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Numbers 17K14382 and 19H04626.