Seismic Site Response of the Mainland China Using Regional Phases.

Seismic site response is a key factor in seismic hazard analysis. We have estimated the site response data using the regional phase S n for the mainland China from 484 events, with 1188 stations, both permanent and temporarily. We have used the Reverse Two Station method (RTM) to eliminate all the path and source effects. We have also gone carefully through the dataset and worked to isolate and in some cases repair problems with instrument response. The results for the North China Craton area and the North China plain show amplification and deamplification, respectively. This might be the effect of a thick sequence of sedimentary rocks and younger sediments. The results for most south China region show a small deamplification, while the results at lower Yangtze plain show strong amplification. The S n site response results show clear deamplification at the boundaries of large geological blocks, e.g. the Ordos, Tibet and Tianshan; however, the site response results show average in the middle of geological block, meaning not much amplification or deamplification relative to others. Other than the 0.5 Hz S n site response results, we also estimated the higher frequency up to 4.0 Hz site responses. Unlike the 0.5 Hz, higher frequency signal results show more small geological blocks. In other words, high frequency site response correlates with short-wave topographic structures. We are planning to extend our work on S n to include the site amplification using L g phases. This should help us determine the origin and interpret our site amplification analysis.