Long-Period Velocity Pulses at Near-Fault Region During the 2016 Kumamoto Earthquake, Japan

Date: 4/25/2019

Time: 06:00 PM

Room: Fifth Avenue

During the main event of the 2016 Kumamoto earthquake (M_W7.0~7.1), Japan, surface ruptures were confirmed in a wide region and were accompanied with wide range of permanent displacement. In the vicinity of the seismic faults, seismic intensity of scale 7 in the JMA intensity scale and large-amplitude pulse-type ground motions with period of 1 sec were observed at the Mashiki Town in the fault parallel direction. These pulse-type ground motions caused severe damage to wooden houses, which resulted in a damage zone with a width of about 1 km at the central part of the Mashiki Town. Moreover, at the Nishihara village and the K-NET Ichinomiya, a long-period pulse with dominant period of about 3 sec was observed, which could cause damage to long-period structures including super-high-rise and seismically isolated buildings. In the seismically isolated hospital building in Aso City about 3.6 km away from the K-NET Ichinomiya, the relative displacement of seismic layer from recorded orbiter showed smaller deformation at isolation devices than expected. This implies that amplitude of long-period pulses were spatially variated depending on location between sites and the seismic faults. In this study, we constructed a characterized seismic fault model and performed theoretical simulation of strong ground motions near the seismic faults. Thin Layer Method is used as a numerically effective tool for ground motions simulation for the seismic faults with surface ruptures. The spatial variation of the strong ground motions including the Aso area in the northeastern part of Kumamoto Prefecture could also be simulated by a characterized seismic fault model. The validity of the slip distribution of the fault model was also examined based on the comparison of surface distribution of permanent displacement between calculated results from the seismic fault model and those from crustal deformation by InSAR images.

Presenting Author: Toshimichi Kido

Authors