GENERATION MECHANISM BEHIND THE STRONG VELOCITY RECORD AT MIFUNE INTERCHANGE ON KYUSHU EXPRESSWAY DURING THE 2016 KUMAMOTO EARTHQUAKE

Abstract

 In April 2016, a series of earthquakes named as the 2016 Kumamoto earthquakes struck at central Kyushu area in the southwest of Japan. During the first and main shocks, large velocity records were obtained at the Mifune interchange on the Kyushu expressway. The records were much larger than observation records in the surrounding area. Our research focuses on studying the generation mechanism of the strong velocity records at the Mifune interchange. In this study, we conduct microtremor observations and estimate shallow S-wave velocity structures at Mifune interchange and two other neighborhood locations. Based on the obtained shallow S-wave velocity structures, the velocity waves at Mifune interchange were simulated for both the first and main shock events. The simulation results agreed well with the observation records. The study found that the site amplification by the shallow subsurface soil layer was one of the reasons causing strong velocities at the Mifune interchange on the Kyushu expressway.