SEGJ Technical Conference

Aftershock observation and continuous microtremors observation of the 2011 off the Pacific Coast of Tohoku Earthquake (Mw9.0) in the middle part of Ibaraki Prefecture

Abstract We performed the aftershock observation of off the Pacific Coast of Tohoku Earthquake (Mw9.0, March 11/2011) in the East Ibaraki Plateau of the middle part of Ibaraki Prefecture. Strong ground motions larger than the maximum velocity of 70 cm/sec were observed at Hokota (IBR013 of K-NET) located in the south from the East Ibaraki Plateau, due to a short distance from the fault plate of the main shock. In the observation, therefore, we distributed 15 stations in and around the East Ibaraki Plateau where the permanent observation stations such as K-NET have not been installed, to understand spatial distributions of earthquake ground motions in this area. We also aimed to understand the underground structures, by both analyses of H/V spectral ratios of Coda waves for earthquake recordings and cross-correlations using the seismic interferometry method for continuous microtremors recordings. The tendency of H/V spectral ratios of Coda waves and group velocities of microtremors was matched well, especially for the area from the seacoast of Pacific to the Tsukuba Mountains. Also, these results were in good agreements with the existent geological data.