Abstract: Based on near-source conditions, we used waveform data observed by the Beijing Digital Telemetry Seismic Network and obtained source spectrum, corner frequency and zero frequency amplitude values of 989 earthquakes with magnitude larger than M_L2.0 occurred in the capital circle of China and surrounding area from January 2002 to June 2006 by the Brune model. Some relevant formulas had been used for calculation of a few focal dynamic parameters, such as rupture radius, seismic moment, seismic energy, stress drop, apparent stress, and so on. The scaling relations of these dynamic parameters and characters of the temporal-spatial variations before the Wen'an M_S5.1 earthquake in Hebei Province of July 20, 2006 had been analyzed. Results show that apparent stress, stress drop, seismic energy and rupture radius ratio appeared relatively high in some focus areas before the Wen'an M_S5.1 earthquake. These areas were mainly distributed in the North China Plain. It could be seen from the time curves that apparent stress, stress drop, seismic energy and rupture radius ratio and other parameters had shown a significant increasing process before the Wen'an M_S5.1 earthquake, but corner frequency showed a trend of decreased variation. This result might be related to the increasing process of stress in the North China Plain before the Wen'an M_S5.1 earthquake.

Key words: Focal dynamic parameters, Temporal-spatial variation, Wen'an earthquake, Capital circleof China