Abstract
We have conducted observation of earthquake ground motion due to aftershocks of the 2016 Kumamoto earthquake at 26 temporary stations in damaged areas of Kumamoto city, Mashiki town, Nishihara village and Minami-Aso village (partly in Aso city) in Kumamoto prefecture, Japan. Continuous recordings of ground acceleration were acquired in a period of about 1 month after the occurrence of the main shock on April 16, 2016. This preliminary analysis of the observed records clearly indicates strong effects of local geological condition in the heavily damaged districts in Mashiki town and Nishihara village. Spectral ratios of the ground motions at the stations in the severely damaged districts to those at the reference sites are characterized by large amplitudes at periods of 0.5–1 s. Peak ground velocities and seismic intensities are also large at the sites. Seismic intensities at the stations in the damaged districts are larger by an intensity of one at the maximum than those at the stations with the minor damage. The ground motions at the stations in Kumamoto city are rich in later phases with long duration suggesting basin effects. However, site amplification effects could not clearly be identified at the stations in the Minami-Aso area from the results in the conventional spectral ratio approach.
Highlights
Heavy damage was experienced in Kumamoto prefecture, Japan, during the 2016 Kumamoto earthquake with an MJ of 7.3 on April 16, 2016, and its foreshock with an MJ of 6.4 on April 14, 2016
The hypocenter of the foreshock was determined to be beneath the northeastern part of the Hinagu fault zone, while the main shock occurred along the Futagawa– Hinagu fault zone (e.g., Asano and Iwata 2016; Shimizu et al 2016)
MK01 in Fig. 1b is located near a main governmental office of Mashiki town, where strong motion records of the main shock were obtained by a seismic intensity meter
Summary
Heavy damage was experienced in Kumamoto prefecture, Japan, during the 2016 Kumamoto earthquake with an MJ of 7.3 on April 16, 2016 (main shock in the following), and its foreshock with an MJ of 6.4 on April 14, 2016. The heavy damage was concentrated in the focal area in Mashiki town in Kumamoto prefecture.
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