Analysis of the Trapped Wave Recorded in Kunlun Fault Zone

Abstract

Artificial seismic experiment was deployed on the fault zone generated by the Kunlun Ms8.1 earthquake on Nov. 4, 2001 and the seismograms recorded on two profiles, one along and the other across the fault zone, were analyzed and processed for the purpose of fine structure investigation of the fault zone with the guided wave trapped in fault zone. The analysis includes amplitude spectra calculation, group velocity and dispersion curves extraction, S wave velocity structure inversion with surface wave methods and the estimation of Q factor with an amplitude-ratio method. The result of field experiment reveals that the time delay between the S wave and trapped wave train increases with the epicentral distance. The site effect related to the fault zone is also observed in seismogram recorded on the stations located outside the fault zone. The final result suggests that the fracture zone of Kunlun fault is about 250m wide, and has a layered internal velocity structure and an average Q of 15, while the average Q of wall rocks is 30. It is also found that the width of rupture zone generated by the Kunlun earthquake is the same as that of Landders Ms7.6, California, earthquake, although both the magnitude and the length of fracture zone of the former are much larger than those of the latter.