OBSERVATION OF AFTERSHOCK DUE TO THE 2018 WESTERN SHIMANE PREFECTURE EARTHQUAKE AND MICROTREMOR OBSERVATION IN THE STRUCTURAL DAMAGE AREA OF SHIMANE PREFECTURE, JAPAN

Abstract

 An earthquake (Mj6.1) occurred in the vicinity Ohda city western Shimane Prefecture in Japan on April 9, 2018. We conducted aftershock (strong motion) observation at several temporary sites in the area with housing damages. Characteristics of site amplification effect of the temporary sites were understood from analysis of seismic data. Also, microtremor observations were carried out to estimate the characteristic of ground vibration in the damage area. Microtremor H/V spectra and a distribution of the predominant period were obtained from observation data. In addition, we checked the relationship between site effects S-wave velocities, H/V of microtremor and strong ground motion. As a result, it was found that maximum thickness of the weak soil subsurface layer is 40m and a short period component of predominant period about 0.2-0.4 seconds may have influenced structural damage.