[S-CG47] Crustal fluids and deformation

[SCG47-01] Post-seismic slow strain changes and groundwater level changes in the case of the SSK observation site of AIST

*Yuichi Kitagawa¹ (1.Tectono-Hydrology Research Group, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology)

Keywords:strain, groundwater, post-seismic change

In order to research short- and intermediate-term forecast of the Nankai megathrust earthquake, we observe crustal movement and groundwater at observation sites in Aichi Prefecture, Kii Peninsula and Shikoku, in particular focus on monitoring of short-term SSEs on the plate boundary. When the earthquake (M6.3) occurred on May 10, 2019 at the Hyuga-nada, slow strain changes were post-seismically observed at the Tosashimizu-Matsuo (TSS) observation site of AIST, however it is presumed that the post-seismic strain changes at the TSS are likely to be caused by the local changes around the TSS due to the shaking of the earthquakes. We investigated whether similar strain changes were occurred at the Susaki-Ootani (SSK) observation site of AIST, which is near the locked part of the plate boundary of the Nankai Trough as with TSS. According to checking of changes of the strain and groundwater level at the SSK after the M5 or more earthquakes around the Shikoku and the earthquakes with a seismic intensity of 2 or more in Susaki city, Kochi Prefecture, seven cases of post-seismic slow clear strain changes were found. In two of the seven cases, the effects of rainfall appear to overlap with post-seismic changes, so careful investigation is required. In some cases, the groundwater level in observation wells at the SSK had post-seismically changed at the same time as the strain changed. These observation results are introduced.