Kotaro TOMIDOKORO

Related earthquake damage and terrain classification-Examination of Mid Niigata Prefecture Earthquake in Ojiya City-

Takaaki IKEDA

Background
Various studies and reports have been performed on the relationship between earthquake damage and topographic classification, and it is thought that there is a relationship. According to previous studies and reports, it is said that house damage tends to be more frequent in topographical classification where the ground is soft and its boundaries. In the past, analysis was done by overlaying building damage data and topographic data. Currently, Disaster Victim Certificate issued by municipalities are used for building damage data, and Land Condition Maps and Landform Classification Map for Flood Control issued by the Geographical Survey Institute are used for topographic data. These data do not have a high accuracy but since alternative may valid data is small, it inevitably used at present.
Objective
This study, carried out the study the relationship between earthquake damage and terrain classification intended for Ojiya of Mid Niigata Prefecture Earthquake in 2004. Analysis to superimpose the building damage data and terrain data in the same manner as in the previous studies. There are two things to do before considering the relevance. The first is a detailed analysis of building damage information. In this study, we propose a damage judgment method that can be replaced with a disaster certificate, judge the damage, and update the damage data. The second is a detailed analysis of terrain information. In this study, we estimate the ground characteristics by on-site geophysical survey and update the topographic data. Then, the relation between building damage and topographic classification is examined using the updated data.
Result
Comparing the natural frequency of the ground in the area where the building damage occurred frequently, most of the building damage distribution coincided with the range showing less than 2.00Hz and the boundary.
Comparing the shear wave velocity structures of the damaged and undamaged buildings, the damaged building has a low-velocity soft layer at a depth of about 5m.
When the damage and average shear wave velocity from 1 to 30m in depth were compared, the relation between average shear wave velocity in 4 to 7m in depth and damage was seen.