Site response at the Dobutsu station in Aomori prefecture, Japan during strong and weak earthquake ground motion

Abstract

Since 2001, the Dobutsu seismic intensity observation station has recorded strong ground motions with the intensity of ≥5 on the Japan Meteorological Agency (JMA) seismic intensity scale for 13 times. Moreover, weak to strong seismic motions have been recorded. In this study, the amplitude dependence of the site response was investigated using earthquake records at the Dobutsu station. First, boring and microtremor surveys were conducted. Then, seven strong motion records and ten weak motion records were analyzed. Finally, the horizontal-to-vertical spectral ratio of earthquake motion was used to confirm the amplitude dependence. Results showed that the peak frequency, F_p, during weak motions is 1.6 Hz but it becomes 1.4 Hz when the peak ground velocity is ~20 cm/s.