SEGJ Technical Conference

Microtremor Array Survey at the Long-Period Ground Motion Recording sites during the 2016 Kumamoto Earthquake

Abstract On April 16, 2016, an inland crustal earthquake (MJMA 7.3) occurred in the Kumamoto prefecture. Several strong motion stations recorded long period ground motions with response acceleration in the period range from 2 to 5 seconds exceeding 800 cm/s2. It is rare that these long period ground motions were observed during the inland crustal earthquake, and it is very important to elucidate the cause in considering the earthquake resistance of long-period structures. Therefore, in order to understand the cause of these long period ground motions during this earthquake, we focused on the site effects. We carried out microtremor array observations at three stations which recorded the long period ground motions, and estimated the underground velocity structures. And then, based on them, we calculated site amplification characteristics. As the result, it was found that the site effects strongly influence the long period ground motions observed during the 2016 Kumamoto earthquake because calculated site amplification characteristics have large amplification factors in the period range from 2 to 5 seconds.