Abstract

The design of buildings and structures in earthquake-prone regions must be based on information relating to expected seismic effect. Estimations of time domain and spectral parameters of ground motion are obtained by empirical relations that connect these to earthquake magnitude, distance, and local soil conditions. In the Taiwan region, the models for estimating ground motion parameters were obtained recently on the basis of recordings of small to moderate (5.0 ≤ ML ≤ 6.5) earthquakes. A large collection of acceleration records from the recent ML 7.3 (Mw 7.6) Chi-Chi earthquake and aftershocks makes it possible to test the applicability of the established models in the case of larger events. We compared modeled Fourier amplitude spectra and peak accelerations and response spectra, which were calculated using the stochastic approach from the Fourier spectra, and the data obtained during the mainshock and the largest aftershocks (ML 6.6-6.8). It has been shown that the previously established regional spectral model (Fourier spectra of ground acceleration) may be applied for evaluation of ground motion parameters for earthquakes (reverse faulting) of magnitudes up to ML 6.8-7.0 and hypocentral depth more than 10 km. To satisfy to the peculiarities of ground-motion propagation during shallow (depth less than 10 km) events, the model should be revised. The analysis of accelerograms from the mainshock (ML 7.3, depth 8 km, 314 records) and large shallow aftershock (ML 6.8, depth 10 km, 350 records) allows the authors to obtain the revised spectral model for average-soil conditions.

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