A Study on the Relationship Between Building Damage and Shallow Subsurface Ground in the 2015 Nepal Gorkha Earthquake

Many buildings collapsed in the 2015 Nepal-Gorkha earthquake. Numerous buildings collapsed on hills and slopes. On the other hand, damaged buildings were scattered in the Kathmandu basin. Damage of buildings on hills and slopes is due to the effects of topography, and damage of buildings scattered in the Kathmandu basin is due to vulnerability of buildings. However, as an exception, damaged buildings were concentrated in the Gongabu area I Kathmandu, despite its mostly flat terrain. We considered the influence of ground motion characteristics of near surface. Therefore, the authors carried out microtremor array survey to clarify the S-wave velocity structure up to 30 m depth as a characteristic of the subsurface ground. In general, the average S-wave velocity up to 30 m (AVS30) is related to the amplification of seismic ground motion, and it is said that the amplification of seismic ground motion greatly affects building damage. As a result, the relationship between AVS30 and building damage was not clear. However, assuming that an S-wave velocity of 200 m/s is the engineering base layer for seismic resistance evaluation, using an index that combines the slope of the upper surface of the engineering base layer and AVS30, the relationship with building damage and these indices become clear. It was found to be effective as a risk evaluation method.