Spectral analysis of Zhangbei earthquake series

the source spectra of P and S wave for the digital records of 146 earthquakes from Jan. 1998 to Nov. 1999 in Zhangbei area recorded by Shijiazhuang telemetered seismic network are analyzed. In the analysis the corner frequency, seismic moment, focal radius, stress drop, average displacement and spectral energy are calculated. The variation of corner frequency and stress drop with time are analyzed, and the relations between focal parameters are discussed. The results indicated that the stress drop and corner frequency both showed anomalies before Zhangbei M_L5.6 earthquake occurred on Mar.11,1999. Meanwhile, S wave is more sensitive to the change of environment than P wave. The focal parameters are correlative with magnitude in some extent.