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2010年6月22日和2012年11月20日在宁夏回族自治区银川市永宁县发生了2次M_s4.5地震,在银川市及周边地区引起了强烈震感。为了更好地认识这2次地震的发震构造,利用宁夏及邻近几个省份区域台网的近震波形资料,首先通过HyP2000绝对定位得到震中位置及余震震中分布;然后使用TDMT矩张量方法反演了震源机制解与震源深度。结果显示:2010年6月22日地震节面Ⅰ走向208°,倾角89°,滑动角-164°,节面Ⅱ走向117°,倾角74°,滑动角-2°;2012年11月20日地震节面Ⅰ走向284°,倾角79°,滑动角12°,节面Ⅱ走向192°,倾角78°,滑动角169°。综合Snoke法,得出这2次地震主控断层均为走向NNE、倾向NWW的右旋走滑断层;前者带有少量的拉张分量,后者带有少量逆冲分量,矩震级分别为M_w4.5和M_w4.3。根据HyP2000精定位、TDMT矩张量拟合误差和sPn深度震相等3种方法确定最佳震源深度分别为22km和8km,均属浅源地震。从定位震中和震源机制解来看,虽然2次地震震中仅差13km,但前者震源比后者深,分析其原因,可能为2012年11月20日地震由银川断裂的主断裂控制,而2010年6月22日地震由银川断裂的南支分断裂控制。
June 22, 2010 and November 20, 2012 Two M_s4.5 earthquakes occurred in Yongning County, Yinchuan City, Ningxia Hui Autonomous Region, causing a strong sense of earthquake in and around Yinchuan City. In order to better understand the seismogenic structures of the two earthquakes, the near epicenter waveform data of regional networks in Ningxia and several neighboring provinces were used to obtain the epicenter location and the epicenter distribution of the aftershocks through the HyP2000 absolute positioning. Then, the TDMT moment tensor method Focal mechanism solutions and focal depths were inverted. The results show that: on June 22, 2010, the section I of earthquakes reaches 208 °, the angle of inclination is 89 °, the angle of sliding is -164 °, the angle of heading II is 117 °, the angle of inclination is 74 ° and the angle of sliding is -2 °. On November 20, 2012 The section I of the earthquakes has an angle of 284 °, an inclination of 79 °, a sliding angle of 12 °, a section II of 192 °, an inclination of 78 ° and a sliding angle of 169 °. Based on the Snoke method, it is concluded that the two main earthquakes are both strike-NNE and NWW dextral strike-slip faults. The former has a small amount of tension component with a small amount of thrust component and the moment magnitudes are M_w4 .5 and M_w4.3. According to HyP2000 precision positioning, TDMT moment tensor fitting error and sPn depth shock equalization, the best depth of focal point is 22km and 8km, respectively, which are all shallow earthquakes. According to the positioning epicenters and focal mechanism solutions, although the epicentral distances of the two earthquakes are only 13 km, the source of the former is deeper than that of the latter. The reason for this may be that the earthquake was controlled by the main rupture of Yinchuan fault on November 20, 2012 and 2010 The June 22, 2008 earthquake was controlled by the southern branch fault of the Yinchuan fault.