Field Investigation on Dynamic Behavior of Soil and Building Structures in the Near-Fault Region of the 1999 Chi-Chi, Taiwan Earthquake

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The purpose of the project is to understand the damage mechanism of structures built in the near-fault regions based on the field investigation of the 1999 Chi-Chi, Taiwan, earthquake, in which we have invaluable strong ground motions observed by a recent network of high resolution seismometers. To this end we deployed temporarily an aftershock observation network and we also conducted microtremor observeation for both soil structures and building structures to understand their dynamic behavior. We first investigate observed strong motions based on the ground property of the sites in a near-fault region and estimate strong motions for sites without observed records.In the year 2000 we conducted for two weeks microtremor array and single-station survey in the Taichung area in order to delineate the S-wave velocity structure of the Taichung Basin. Microtremors in typical buildings in Taichung were also measured. We then performed nonlinear analysis of building models established for Japan to understand the damage potential of the observed strong motions in the near-fault region. It turns out that most of the strong motions observed in the near-fault area do not show strong damage potential except for two records, which show the same spectral levels in the intermediate period range (〜1 sec) with the records in Kobe. In the year 2001 we explored underground S-wave structures in the Taipei Basin, which may have much devastating damage if a big event happen in near future. Based on these information we are ready to evaluate damage potential of the structures in Taiwan and we can compare damage potential of buildings in Taiwan and Japan.