SAFETY ASSESSMENT OF UNDERGROUND TANK AGAINST LONG-PERIOD STRONG GROUND MOTION - ESTIMATION OF DEEP SUBSURFACE STRUCTURE BY OBSERVING MICROTREMOR AND STRONG-MOTION IN AKITA DISTRICT -

In considering the safety of oil storage, it is important to grasp the characteristics of long-period ground motion causing sloshing, and it is also useful to investigate deep subsurface structures at the site, as well as to analyze the characteristics of long-period ground motion by the observed earthquake waves. In this study, we conducted the above investigation and analysis in Oga area where Akita National Petroleum Stockpiling Base is located and Akita City/Sanno area around Oga area. As s result, we obtained the following results: 1) In both areas, we estimated deep subsurface structures to reproduce both phase velocity and H/V ratio of microtremor observation records. 2) We confirmed that the group velocity of the strong-motion observation records approximately corresponded to the theoretical dispersion curve of the estimated deep subsurface structures in both areas. 3) According to the estimated deep subsurface structures, the depth of Vs=3km/s to be the seismic bedrock was 0.8km in the Oga area and 1.8km in the Sanno area, revealing that the structure in the Sanno area tends to amplify the long-period ground motion more than that in the Oga area.