A study of site response and regional attenuation in the Longmen Shan region, eastern Tibetan Plateau, SW China, from seismic recordings using the generalized inversion method

摘要

In this study, more than 1600 seismic recordings from 88 small-to-moderate earthquakes during 2009 and 2013, which were recorded at 36 seismic stations, were used to calculate the high-frequency attenuation parameter (kappa(0)). By comparing the kappa(0) of six seismic stations with neighboring strong motion stations, we observed that the surficial soil layers have aggravated the high-frequency attenuation phenomenon. Besides, we found that stations located in crustal low-velocity anomaly areas maintained higher kappa(0) and those located in high-velocity anomaly areas tended to have lower kappa(0). The correlation between kappa(0) and S-wave velocity anomaly showed that, at the 0-10 km depth range, the kappa(0) values clearly decrease as the velocity anomaly increases. The generalized inversion technique (GIT) was adopted to estimate the Q(f) model of the Sichuan Basin (SB) and Songpan-Garze Orogen (SGO), in accompaniment with the site responses of 28 seismic stations. The derived Q(f) model were similar to those obtained from previous studies. Analyses of site responses revealed that the amplification curves and levels of SB and SGO were significantly different. Then, Site responses estimated from the genetic algorithm and GIT were compared. The site response curves of most stations are similar. For stations having significantly different site responses, we investigated by comparing with the results obtained from accelerograms recorded at nearby strong motion stations by applying the horizontal-to-vertical spectral ratio (HVSR) method. The results showed that site responses obtained from the GIT were closer to those of HVSR than those of the genetic algorithm.