2023年沙雅MS6.1地震和2012年洛浦MS6.0地震矩张量反演及震源断层确定

Moment tensor inversion and source fault determination of the 2023 MS6.1 Shaya earthquake and the 2012 MS6.0 Luopu earthquake

  • 摘要: 2023年1月30日塔里木盆地北部新疆沙雅发生MS6.1地震,其附近曾发生过2012年3月9日洛浦MS6.0地震,两次地震均发生在巴楚隆起—阿瓦提凹陷构造带。通过gCAP方法测定了2023年沙雅MS6.1地震和2012年洛浦MS6.0地震的矩张量解,分析了沙雅地震和洛浦地震震源机制与区域应力场的关系,初步确定了其可能的震源断层。结果显示:矩张量反演得到的2023年沙雅MS6.1地震震源机制解节面Ⅰ参数为走向251°、倾角68°、滑动角6°,节面Ⅱ参数为走向159°、倾角84°、滑动角158°,震源机制为走滑型,P轴方位为207°,倾伏角为11°;2012年洛浦MS6.0地震震源机制解节面Ⅰ参数为走向274°、倾角61°、滑动角67°,节面Ⅱ参数为走向135°、倾角36°、滑动角125°,震源机制为逆冲型,P轴方位为20°,倾伏角为13°;两次地震的P轴方位与巴楚隆起—阿瓦提凹陷带NNE向主压应力方向一致;沙雅地震的地震矩M0为7.798×1017 N·m,矩张量解MrrMttMppMrtMrpMtp分别为−0.081,−0.821,0.342,0.064,−0.358,0.685;洛浦地震的地震矩M0为9.076×1017 N·m,矩张量解MrrMttMppMrtMrpMtp分别为0.517,−0.910,−0.353,−0.491,−0.180,0.341,且均属于典型天然构造地震事件。两次地震的震源机制与应力体系关系显示,其震源机制解节面的相对剪应力几乎达到了最大,且震源机制解滑动角与剪应力滑动角相差较小,表明两次地震几乎均发生在构造应力场的最优释放节面上,并主要以剪应力作用体现。结合已有研究,初步推测两次地震震源机制解的节面Ⅱ为可能的发震破裂面,2023年沙雅地震的发震构造可能为阿瓦提凹陷中地壳约30 km滑脱构造带上方NW走向的高倾角捩断层,地震错动方式为右旋走滑,该地震是由于塔里木克拉通北部整体向南天山深部俯冲导致NW向平移断条之间产生撕裂作用;2012年洛浦地震可能与巴楚隆起上盘相对于阿瓦提凹陷下盘NE方向逆冲运动产生的NW走向且断层面SW向倾的发震构造有关。

     

    Abstract: On January 30, 2023, a MS6.1 earthquake occurred in Xinjiang Shaya in the northern Tarim basin. The MS6.0 Luopu earthquake on March 9, 2012 was the latest strong earthquake near the Shaya epicenter. These two earthquakes both occurred in the Bachu uplift to Awati depression tectonic belt. The moment tensor solutions of 2023 MS6.1 Shaya earthquake and 2012 MS6.0 Luopu earthquake were determined by gCAP method. The relationship between focal mechanisms of Shaya and Luopu earthquakes and regional stress regime was analyzed. Finally, the source faults were preliminarily determined. Moment tensor inversion results indicate that the 2023 MS6.1 Shaya earthquake is a strike-slip event with strike 251°, dip 68°, rake 6° for nodal plane Ⅰ and 159°, 84°, 158° for nodal plane Ⅱ, respectively, the Paxis azimuth is 207° and plunge angle is 11°, and that of the 2012 MS6.0 Luopu earthquake is a thrust event with strike 274°, dip 61°, rake 67° for nodal plane Ⅰ and 135°, 36°, 125° for nodal plane Ⅱ, respectively, the P-axis azimuth is 20° and plunge angle is 13°. The P-axis azimuths are both consistant with the principal compressive stress direction in the NNE direction of the tectonic stress field in the Bachu uplift to Awati depression belt. The results of the full moment tensor solutions show that for Shaya earthquake the seismic moment M0 is 7.798×1017 N·m while the moment tensor solutions Mrr, Mtt, Mpp, Mrt, Mrp, Mtp are −0.081, −0.821, 0.342, 0.064, −0.358, 0.685, and for Luopu earthquake the seismic moment M0 is 9.076×1017 N·m while the moment tensor solutions Mrr, Mtt, Mpp, Mrt, Mrp, Mtp are 0.517, −0.910, −0.353, −0.491, −0.180, 0.341, and that both Shaya and Luopu earthquakes belong to typical natural tectonic seismic events. The relationship between the focal mechanisms and the stress regime of the two earthquakes reveals that the relative shear stress of the focal mechanism plane is almost the maximum, and the difference between the rake of the focal mechanism and that of the shear stress is small, indicating that the two earthquakes almost both occurred at the optimal release plane of the tectonic stress field, and are mainly affected by the shear stress. Combined with the previous studies, it is speculated that the nodal plane Ⅱ of the focal mechanism solution of the two earthquakes is the possible seismogenic rupture plane. The seismogenic structure of the 2023 Shaya earthquake may be a high-dip transition tear fault on the NW strike above the 30 km deep detachment tectonic belt of the middle crust of Awati depression, and the earthquake dislocation mode may be right-lateral strike-slip. It belongs to the tearing between NW trending translational fault blocks caused by deep subduction from the northern Tarim Craton to the southern Tianshan tectonic belt. The 2012 Luopu earthquake may be related to the NW striking and SW dipping seismogenic fault generated by the overthrust of the hanging wall of Bachu uplift which is in the NE direction above the footwall of Awati depression.

     

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