【摘要】 基于江苏、安徽、山东和浙江等省区域台网共19个宽频带数字台站的地震波形,采用HypoDD双差定位方法确定了2012年7月20日江苏高邮—宝应MS4.9级地震震中位置,再利用时间域矩张量反演法TDMT_INV获得了其震源机制解和震源深度.反演结果显示:最佳双力偶解为节面Ⅰ走向290°,倾角88°,滑动角-21°;节面Ⅱ走向21°,倾角69°,滑动角-177°,地震矩震级为MW4.95,震源深度约为7~9km.利用滑动时窗相关法提取sPn震相测定震源深度为8.95km,两者一致性较好.随后不同地壳模型和不同震中定位误差对反演结果的影响试验揭示了反演结果具有稳定性.通过以下几种分析:1与利用CAP(Cut and Paste)矩张量反演法得到的结果进行对比;2P波初动投影;3正反演试验探求反演结果不稳定的影响因素等方法,验证了反演结果的可靠性.综合本文研究成果、震后科学考察结果(包括重力测量和地震烈度分布图)及现有的地质构造资料,推测此次地震的发震构造为杨汊仓—桑树头断裂,节面Ⅱ为断层面,是一个右旋走滑兼有少量正断层性质的错动.更多还原

【Abstract】 An MS4.9earthquake occurred in Gaoyou-Baoying,Jiangsu on 20 July 2012.This work determined its focal mechanism and depth through Time Domain Moment Tensor Inversion(TDMT-INV),and analyzed the stability and reliability of the results.Based on the 19 regional broadband seismometers′waveforms from Jiangsu,Anhui,Shandong and Zhejiang seismic networks,we accurately determined the location of the earthquake by theHypoDD first,and then calculated its focal mechanism and depth through TDMT_INV.And we compared this depth that obtained from picking up the sPn phase by patterning correlation coefficients in sliding windows.We tested the results through the following several procedures:1 Experiments by different crustal models and different epicenter location errors;2 Comparing with the result from the CAP method;3 P-wave first motions are projected onto the focal sphere;4 Forward modeling and inversion to research the factors of inversion instability.The nodal plane parameters of the best double-couple focal mechanism are as follows:strike290°,dip 88°and rake-21°;or strike 21°,dip 69°and rake-177°,Mw4.95 and focal depth is 7~9km.We calculated the focal depth by picking up sPn phase and got the 8.95 km result.The results include:1 All angles match well except one dip with 20°variation when we used the Crust2.0model instead of the IASP91 and hold the Q value unchanged.The results are nearly invariable if Q value changes by 100 and holding velocity and density constant.The maximum misalignment of the result is 6°when the epicenter varies within 5km.The result will deviate from the best solution while the epicenter varies by 10 km.2 The predominant focal depth is 8~10km by the CAP method.The results for 8km-focal depth are:strike 19°,dip 65°and rake-180°.3 There are 41 P-wave first motions projected onto the focal sphere,the ratio of inconsistent polarity is 7.3%,and all the contradictions are distributed around the nodal plane.4By forward modeling and inversion,while using the TDMT_INV method to invert the nearly pure strike-slip fault,we proved that the sign of slip will probably reverse if the station distribution concentrates on both ends of the field angle,the inversion results can properly return the forward model while the stations are distributed uniformly.In this case,it is hard to determine the accurate result through the evaluation parameters variance reduction(VR)and the variance divided by the percent double-couple(RES/Pdc).The TDMT_INV method is less dependent on the crustal model.The inversion results do not change much if the epicenter error is within 5km.The method has stability,but stations should surround the epicenter and are distributed uniformly as much as possible while inverting the near pure strike-slip fault.By comparing our results with field investigations after the earthquake(gravity measurement and seismic intensity distribution)and existing data of geological structure,we infer that the seismogenic structure for this event is the Yangchacang-Sangshutou fault,which is of right-lateral strike slip with a small normal component.更多还原