A COMPARISON OF SITE-AMPLIFICATION ESTIMATED FROM DIFFERENT METHODS USING A STRONG MOTION OBSERVATION ARRAY IN TANGSHAN, CHINA

摘要

A seismic observation array for strong motions were deployed to estimate seismic source, propagation path and local site effects in Tangshan, China. About sixty events ranging from M 2.2 to 5.9 were recorded in the past several years. We first separated seismic source, propagation path and local site effects from a linear inversion of S-wave spectra using the data set of 10 events recorded at 8 stations. We next compared site responses from the S-wave inversion and those from other techniques, such as traditional direct spectral ratios of S waves, receiver-function of S waves. From the separation, we found that S-wave quality factor, i.e. Q_s-value, is approximately satisfied with the relation of Q_s = 67 f~(1.1) in the range of frequency from 0.5 to 32Hz. The source spectra follow the G)'2 model of seismic source for low frequencies less than about 12Hz. From the comparison of site responses estimated by the different methods for each soil site, we found that all the methods can extract the same predominant peaks from the responses. The amplifications from direct S wave spectral ratios are well correlated with those from the S-wave inversion within a factor of 2 to 3. While the correlation between the amplifications from S-wave receiver-function and those from the S wave inversion is not good, especially for high frequencies more than 8Hz.