[S-CG45] Science of slow-to-fast earthquakes

[SCG45-P24] Towards adjoint tomography of the Nankai and Kyushu subduction zones

*Samriddhi Prakash Mishra¹, Yoshihiro Kaneko¹, Bryant Chow², Yusuke Yamashita³, Masanao Shinohara⁴ (1.Graduate School of Science, Kyoto University, Kyoto, Japan, 2.University of Alaska – Fairbanks, Fairbanks, Alaska, USA, 3.Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan, 4.Earthquake Research Institute, University of Tokyo, Tokyo Japan)

Keywords:seismic tomography, full waveform inversion, adjoint methods, subduction zone

The Nankai-Kyushu subduction system is a complex seismotectonic region marked by an abrupt transition in the interplate coupling, with a fully coupled megathrust in the northeast. In this study, we utilize an earthquake-based, full-waveform inversion technique termed adjoint tomography, to develop an accurate and high-resolution shear-wave velocity model in the megathrust regions and reveal the crustal structure responsible for the origin of the interplate coupling transition. Adjoint tomography has been previously applied to regional, continental, and global scales, with a proven track record of applicability in subduction regions elsewhere in the world (e.g., Chow et. al., 2022). We first conduct 2D synthetic inversion examples of SH wave problems using a recently developed automated tool (Chow et al., 2020; Modrak et al., 2018). Our target region includes ~150 permanent (Hi-Net, F-Net, and Do-Net) stations as well as ~20 temporary OBS stations in the Hyuganada region. Our synthetic inversion results suggest that the present technique combined with the existing dataset is capable of resolving crustal structure in fine detail and providing an accurate shear-wave velocity model in this region. We present our ongoing efforts toward imaging and understanding the crustal structure of the Nankai and Kyushu subduction zones and its link to spatial variations in megathrust locking behaviour.