MODELING OF GEOLOGICAL STRUCTURE IN PLAIN USED FOR EARTHQUAKE DAMAGE ESTIMATE —A CASE STUDY IN MATSUYAMA PLAIN—

Abstract

 Following the announcement of the result of Nankai Trough Mega Earthquake-Tsunami Estimate from the Cabinet Office of Japan in August 2012, Ehime Prefecture has been carrying out a detailed estimate of damage induced by earthquakes and tsunamis including the Mega Earthquake-Tsunami from July 2012. During the preparatory work for the estimate of hazard, it had been found that seismic intensities over Matsuyama Plain were much lower than expected intensities in consideration of anticipated amplification in the gravel-dominant alluvial plain. A nation-wide geological model authorized through the Headquaters for Earthquake Research Promotion was used as deep-groound model in the followed estimate by Ehime Prefecture. In order to improve amplification characteristics in the part of this model corresponding to the focused area, modification of model was made using the result of a previous research of a systematic microtremor measurement in this plain. Then the modified model was verified by comparison between the measured and estimated seismic intensities during the 2001 Geiyo Earthquake, as well as comparison with actual distribution of damage to housing. Such modification to be applied in future estimates by local governments would be beneficial for better estimates for their people. Therefore, microtremor measurement over a plain with a certain level of accuracy is expected to be used to estimate a geological basin structure below a plain for earthquake damage estimate before obtaining highly accurate geological structure.