A Study of Strong Motion Response Spectrum in West-central Taiwan


In this paper, a total of 901 free-field accelerograms recorded at the stations in west-central Taiwan from 32 earthquakes that occurred in Taiwan area between 1993 and 1999 are separated as four data groups based on PGA levels, the station sites are classified into three types by their dominant periods of acceleration response spectra. The characteristics of response spectra in regard to both earthquake intensity and station type are analyzed. In order to highlight the behavior of the Chi-Chi mainshock, weveral kinds of comparisons of the near-fault responses have been made with those of far-field data. The results show that the response spectra increase generally with the earthquake intersith of all stations. The spectral shape in ling period regions become more predominant if the soil condition is softer. The mean response spectra plus one standard-deviation of the Chi-Chi mainshock are significantly larger than the required values of the curtrent seismic design code. In terms of the long-period range, the spectra of the Chi-Chi mainshock are larger than the mean value of 32 events by more than 200 times. The spectral rations of vertical to horizontal component almost exceed 2/3; this phenomenon reflects the intensified vertical ground motion due to the thrusting movement of the Chelungpu fault. Therefore, a modified design code is suggested for applications to near-fault areas.

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