Geotechnical Damage Caused by the 2016 Kumamoto Earthquake, Japan

Abstract

On the 16th of April 2016, the Kumamoto earthquake (Mw 7.0) hit the Central Kyushu Region, Japan, following a Mw 6.2 shock on the 14th of April. The earthquake sequences caused severe damage in Kumamoto Prefecture. This paper presents quick reconnaissance results focusing on geotechnical damage features, which were observed during field investigations immediately after, one, and two weeks after the main shock. The damage surveys were carried out in southern Kumamoto City, Mashiki Town, Aso Caldera area and their suburbs. In southern Kumamoto City, evidence of liquefaction was found at many locations, and some buildings and river levees suffered from significant settlement and deformation; damage to an embankment of Kyushu Highway also seemed to be the result of liquefaction. The majority of the damaged residential houses were found in Mashiki Town and its suburbs, which may be linked to intense earthquake motions associated with the seismic fault location. In Aso Caldera area, a number of moderate to large scale landslides and their significant impact to structures were observed. The greater part of landslide masses in Aso Caldera area was a mixture of volcanic ash, andsol, a highly porous dark-colored material comprising of volcanic ash mixed with organic matter, and pumice. These porous materials might have experienced significant strength reduction during the earthquake.