MECHANISM OF THE GRABENS THAT FORMED IN THE ASO CALDERA DURING THE 2016 KUMAMOTO EARTHQUAKE

Abstract

During the 2016 Kumamoto Earthquake, many special belt-like subsidences called “grabens” occurred in the Aso Caldera, and houses were severely damaged. According to the measurement results of SAR, a horizontal displacement of 2 to 3 m was generated in the area where the grabens occurred. A lake was formed in this area around 9,000 years ago. A soil investigation showed that the bottom of the old lake was bowl-shaped, and a special clay was deposited there. A residual deformation analysis showed that the soft clay flowed due to the earthquake, causing the grabens at the ground surface.