2020年3月20日西藏定日MS 5.9地震总结

2020年3月20日西藏定日M_S 5.9地震发生在申扎—定结断裂带分支断裂附近，震源机制解反演结果显示，本次地震为近NS走向断层产生正断层型错动的结果，与区域构造特征一致；地震序列跟踪发现，主震与最大余震的震级差为2.8，主震释放能量占全部序列的99.99%，属于孤立型地震序列。系统梳理地震发生前出现的地震活动和地球物理观测等异常，结果如下：震中附近震前存在年尺度和月尺度的热红外长波辐射异常；对震中附近异常进行回溯，发现震前存在地震发生率和地震危险度D值异常；震中300 km范围内无地球物理观测手段。通过对本次地震进行总结分析，以期为地震监测能力较低的定日地区积累宝贵的震例资料。

Summary of the Dingri MS 5.9 earthquake in Tibet on March 20, 2020

The Dingri M_S 5.9 earthquake occurred near the branch fault of the Shenza-Dingjie fault on March 20, 2020. The inversion result for focal mechanism solution shows that the earthquake is the result of a normal fault type dislocation of near NS direction strike-slip faults, which is consistent with the regional structural characteristics; the process of earthquake sequence shows that the magnitude difference between the mainshock and the largest aftershock is 2.8 and the energy released by the mainshock accounts for 99.99% of the total sequence; therefore, the mainshock belongs to an isolated type sequence. Taken earthquake activity anomalies and geophysical data before the mainshock together, a systematical study indicates that, there are annual scale and monthly scale thermal infrared longwave radiation anomalies before the earthquake; Backtracking of the anomalies near the epicenter, there are anomalies of the earthquake occurrence rate and the D-value of earthquake risk degree before the earthquake; there is no geophysical observation within 300 km of the epicenter. The summary and analysis of this earthquake have accumulated valuable earthquake case data for the Dingri area with low monitoring ability.