Contemporary deformation and seismicity analysis in Southwest Japan during 2010-2018 based on GNSS measurements

A significant amount of work has been conducted in the Japanese islands on high-precision positioning, surveying, natural disaster mitigation, reference frame, and datum definitions; however, there is substantial scope for exploring the current seismotectonic activity of Japan, which would provide further awareness of disaster management. The short recurrence time of great inter-plate earthquakes and well-recorded geodetic observations provide one of the best examples to analyze the combination of contemporary deformation and seismic intensity in Southwest (SW) Japan. In the current study, we analyzed three districts of SW Japan which include mainly Kyushu district and parts of Chugoku and Shikoku districts. We predicted Global Navigation Satellite System (GNSS) measurements based on Amurian-fixed reference frame AREF) velocities with the help of singular spectrum analysis (SSA) method and examined the regional deformation from April 01, 2010 to December 31, 2018. In addition, we analyzed the earthquakes clustered calculated by the nearest neighborhood distance method, which showed prominently bimodal seismicity of SW Japan and revealed the existence of two statistically distinct earthquake populations. The events inside a cluster were normally close to their nearest neighbors, whereas events from distinct clusters were comparatively aloof from each other. Finally, the paper provides the spatial strain and rotational rate variation for selected seismotectonic districts that are in relatively good agreement with the seismic deformation inferred from earthquake focal mechanisms. We believe that our integrated approaches would provide a better insight into the active deformation of SW Japan.