S-WAVE VELOCITY PROFILE OF RESIDENTIAL VOLCANIC SOIL EMBANKMENT COLLAPSE DUE TO 2018 HOKKAIDO IBURI TOBU EARTHQUAKE

Abstract

 In the 2018 Hokkaido Iburi Tobu earthquake, liquefaction occurred in residential embankments constructed of volcanic ash soil in the Satozuka area, Kiyota-ku, Sapporo, more than 50 km away from the epicenter. Furthermore, disasters such as subsidence and inclination of houses occurred due to the flow of embankments. In this study, surface wave exploration was carried out 3 weeks after the occurrence of the earthquake, as an attempt to quickly evaluate the ground properties over a wide area. From a series of survey results, the trend of change of V_S and N - value was consistent. Therefore, it was found that the embankment properties after the earthquake can be evaluated from the V_S distribution obtained from surface wave exploration. The consistency of the V_S reduction region and the ground subsidence distribution in the quasi-three-dimensional V_S distribution was confirmed. Therefore, the quasi-three-dimensional V_S profile can spatially evaluate the relationship between V_S due to embankment runoff and land subsidence.