Investigation of Ishigaki damage factor using ground structure by microtremor measurement and three-dimensional ground map of Kumamoto Castle

Abstract

So many stone walls of Kumamoto castle were seriously damaged during 2016 Kumamoto Earthquake. Many places of these damaged stone walls were rapped with past reconstructed place, therefore it seems that these damaged stone wall place have a close relationship with its ground structure. From the viewpoint of cultural property protection, boring surveys that involve destruction are limited to areas necessary for Kumamoto castle restoration work, and the ground structure within Kumamoto castle area was partially clarified. In this study, microtremor surveys were carried out at points where boring data were insufficient. Then, by supplementing the boring data with newly stratum divisions obtained by these microtremor analysis, we created the three-dimensional ground map that can display the old topography of Kumamoto Castle Ruins. As a result, it was suggested that the Aso pyroclastic flow deposit layer, the thickness of the embankment and the degree of depth from the ground surface to the hard andesite layer affected the earthquake damage of stone walls of Kumamoto castle.