2012年江苏高邮、宝应交界MS4.9地震发震断层参数测定
Determination of Fault Plane Parameters of the 2012 Gaoyou—Baoying MS4.9 Earthquake in Jiangsu Province

基于一维单侧有限移动震源模式,根据地震波传播过程中的多普勒效应,分别利用P波和S波拐角频率的方位变化,反演2012年7月20日江苏高邮、宝应交界MS4.9地震的发震断层面参数。P波和S波拐角频率的反演结果一致显示:本次地震的断层面破裂方向为232°左右,破裂面呈NE-SW向;地震马赫数v/c为0.2左右,平均破裂速度小于S波速度,破裂长度较短,为0.2~0.3 km左右。破裂面方位与震源机制解、宏观烈度调查和余震精定位的研究结果具有一致性,结合震区周边的地质构造背景,分析认为滁河断裂很可能是高邮、宝应交界MS4.9地震的发震构造。
Based on a 1D finite moving source model propagating unilaterally with uniform velocity, the rupture transmission in one direction is superior to that in other directions.According to the Doppler Effect in the earthquake rupture process, the seismic wave frequency received by earthquake stations changes in different directions and thus, we can use the directional change of the corner frequency of the P or S waves to obtain the source parameters of the fault plane.In this article, the azimuth of rupture propagation direction and source parameters of the fault plane of the July 20, 2012, MS4.9 earthquake at the boundary zone of Gaoyou and Baoying in Jiangsu Province are obtained using the directional change of the corner frequency of the P and S waves, respectively.The azimuth angle of the fault plane for this earthquake was determined to be 232° by the P waves and 233.5° by the S waves, the seismic Mach number (v/c) was about 0.18 by the P waves and 0.23 by the S waves, and the fault length was about 0.26 km by the P waves and 0.18 km by the S waves.The result inverted by the corner frequency of the P and S waves is consistent, which shows that the azimuth angle of the fault plane for this earthquake was about 232°. Because of the lack of a near-station record at an azimuth of 49°, the inversion method is based on a 1D finite moving source model propagating unilaterally with uniform velocity.Therefore, the result of a rupture azimuth of 232° cannot represent a rupture propagating in the direction from NE to SW;it only indicates that the rupture surfaces were aligned in that direction.The seismic Mach number was about 0.2, which shows that the rupture velocity was smaller than the S wave velocity, and the fault length was about 0.2~0.3 km. Many scholars have studied the seismogenic structure of the earthquake on July 20, 2012, using a variety of methods such as focal mechanism solutions, field seismic intensity investigations, and relocation for aftershocks;however, the results have not been the same.The results of focal mechanism solutions show that the strike angle of one fault plane is 14°~28° in the NNE direction, whereas the strike angle of the other is in the NWW direction.Analysis shows that the fault plane might be in the NNE direction;however, the results of both field