Differences between Fault-Normal and Fault-Parallel Components of Horizontal Ground Motion in Wenchuan Earthquake

Totally 113 groups of horizontal ground motion were selected from the Wenchuan earthquake to study the influence of fault strike on horizontal ground motion. Differences between fault-normal (FN) and fault-parallel (FP) components were researched by comparing the peak ground acceleration, duration, response spectra, amplification factor and characteristic period. The research results show that when fault distance is less than 50 km, peak ground acceleration of the FN component is larger than that of the FP component, and the mean ratio of their peak ground accelerations is slightly affected by site conditions; durations of the two components both increase with the fault distance. When the fault distance is less than 100 km, the difference of their durations under site class Ⅰ is larger than that under site class Ⅱ. In near-fault areas, the mean ratio of their response spectra is larger than that of their amplification factors, and the differences of their response spectra and amplification factors are more obvious under site class Ⅰ than under site class Ⅱ; characteristic periods of the two components show a sufficient difference, and site conditions have a large effect on the mean ratio and difference of their characteristic periods.