[J09-P] Poster

[J09-P-04] Exponential pore pressure/groundwater level changes associated with the 2016 Kumamoto Earthquake (Mj7.3) observed at Tono region, central Japan

^○Yasuhiro Asai, Hiroshi Ishii, Osamu Murakami (Tono Research Institute of Earthquake Science, Association for the Development of Earthquake Prediction)

Clear exponential pore pressure/groundwater level changes associated with the 2016 Kumamoto Earthquake (Mj7.3) were observed at borehole observation sites “STG200 and STG200N" in Mizunami Underground Research Laboratory (MIU), and TGR350 borehole observation site located approximately 500m south of MIU, in the Tono region, central Japan (Hypocentral Distances are approximately 665km). These observation sites are located approximately 3 km southeast of 16 closely clustered well where were observed co-seismic groundwater level/pressure changes (King et al, 1999; JGR).
Amount of pore pressure changes in STG200 and STG200N are 30 and 28 kPa-rise, respectively, and groundwater level in TGR350 is 2.3m-rise. At the STG200N site, continuous in-situ stress recorded by the borehole stress meter (Ishii and Asai, 2013; EPS). In order to recognize the relationship between the co-seismic pore pressure changes and the seismic waves, we compared the 20 Hz sampling pore pressure and stress records before and after the occurrence of 2016 Kumamoto Earthquake (Mj7.3). As the result, pore pressures begin to increase just after the maximum amplitude of seismic waves (dynamic stress variations) passed through our site.
We will present the details of these pore pressure/groundwater level changes, and attempt to clarify the qualitative/quantitative model for the co-seismic pore pressure/groundwater level changes.