2004年阳江M_S4.9地震震源参数分析

Analysis on the source parameters of Yangjiang earthquake with M_S4.9 in 2004

利用广东数字地震台网的资料计算了2004年9月17日广东阳江MS4.9地震的震源机制为:节面走向57°,倾角47°,滑动角69°,主压应力方向342°,倾角0°,主张应力方向252°,倾角75°,属逆断层性质;地震矩为1.69×1015N.m,应力降为1.7MPa,震源半径为876m。根据阳江地区震前22个ML>2.5的中小地震震源参数,得到一些经验关系。S波拐角频率随时间的变化显示出MS4.9地震前有下降趋势;阳江序列P轴方位角的变化显示出震前4个月应力开始趋于一致。

According to the Guangdong Digital Seismic Network records, the focal mechanism is obtained from the earthquake （Ms4.9） in Yangjiang on September 17, 2004. The strike is 57°, the dip angle is 47° and the rake is 69° of the nodal plane, the azimuth and the dip angle of principal compressional stress axes P is 342° and 0°, respectively; the azimuth and the dip angle of principal extensional stress axes T is 252° and 75°, respectively, the type is reverse faulting. The seismic moment is 1.69×10^15 N · m, the stress drop is 1.7 MPa, the source radius is 876m of this earthquakes. Some relations are obtained by analyzing source parameters of the 22 moderate-small earthquakes in Yangjiang area. The descent trend of corner frequency of S wave is showed by the changes of the time before the earthquake （Ms4. 9）, the azimuth of axes P of Yangjiang sequence show that the stress has begun to be identical in four months before this event.