Title: Advancing centroid moment tensor analysis for offshore earthquakes: progress and future perspectives

Abstract:
Focal mechanisms of earthquakes are essential for understanding seismic processes and the stress field. In previous studies, centroid moment tensor (CMT) analysis of offshore earthquakes has primarily relied on onshore seismic networks located far from the earthquake source region. With the deployment of offshore seismic networks, azimuthal station coverage has significantly improved, offering the potential to improve the stability of CMT solutions. However, seismograms obtained by offshore stations are complex due to strong heterogeneity in subsurface structures and the effects of seawater. Therefore, incorporating three-dimensional (3-D) structural heterogeneity into the CMT analysis is important. This presentation introduces CMT analyses using the S-net offshore stations. The results include thrust events consistent with subduction processes, as well as outer-rise earthquakes concentrated at depths around 20 km. These findings suggest that improved azimuthal station coverage and the use of 3-D seismic velocity structure models contribute to stable CMT solutions. Moreover, we demonstrate that incorporating Rayleigh waves converted from Scholte waves improves constraints on shallow offshore earthquakes occurring in regions with thick seawater layers, such as outer-rise events. This approach notably enhances the accuracy of depth estimates, deepening our understanding of the mechanisms of outer-rise earthquakes. The presentation will conclude with a discussion on future directions.