RESEARCH OF FOCAL MECHANISM AND DEPTH OF TWOMS4.5 EARTHQUAKES IN YONGNING

doi:10.3969/j.issn.0253-4967.2017.01.015

Abstract

Abstract:

TwoM_S4.5 earthquakes happened in Yongning, a county of Yinchuan in Ningxia on June 22, 2010 and November 20, 2012, which were both strongly felt in Yinchuan and its vicinities. In order to understand the seismogenic structure better, we collected the regional earthquake waveform data of Ningxia and nearby seismic networks. Locating main shocks and aftershocks distribution by Hyp2000 and inversing the focal mechanism and depth by TDMT, we got results as follows: for the June 22 earthquake, nodal plane Ⅰ: strike 208, dip 89, and rake -164; nodal plane Ⅱ: strike 117, dip 74, and rake -2. For the November 20 earthquake: nodal plane Ⅰ: strike 284, dip 79, and rake 12, nodal plane II strike 192, dip 79, and rake 169. By means of reference to Snoke method, it is known that the main fractures of the two earthquakes are both strike slip faults with NNE-trending and NNW-dipping, while the former has a small amount of tension component and the latter has a small amount of thrust component. And the moment magnitudes of them areM_W4.5 andM_W4.3. According to Hyp2000 location, TDMT moment tensor fitting error and sPn depth phases, we consider that the focal depths of the two earthquakes are 22km and 8km, both are shallow-focus ones. Though the epicenters of the two earthquakes are 13km apart from each other, the former one is deeper, the reason is that the November 20 earthquake was controlled by the major fault of Yinchuan Fault, while the June 22 earthquake was controlled by south branch of Yinchuan Fault.

Key words: Yongning earthquakes, TDMT moment tensor inversion, the Snoke method, sPn phase

摘要：

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。

关键词: 永宁地震, TDMT矩张量反演, Snoke方法, sPn震相

CLC Number:

P315.3⁺3

JIN Chun-hua, HE Qiu-ju, TIAN Xiao-hui. RESEARCH OF FOCAL MECHANISM AND DEPTH OF TWOM_S4.5 EARTHQUAKES IN YONGNING[J]. SEISMOLOGY AND GEOLOGY, 2017, 39(1): 193-205.

金春华, 何秋菊, 田小慧. 永宁2次M_S4.5地震震源机制及深度[J]. 地震地质, 2017, 39(1): 193-205.

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