2020年7月23日西藏尼玛M_(S)6.6地震总结

Summary of the Nyima M_(S)6.6 earthquake,Tibet on July 23,2020

系统总结2020年7月23日西藏尼玛M_(S)6.6地震的构造背景、震源参数、序列特征和震前异常特征。此次M_(S)6.6地震发生在依布茶卡—日干配错断裂分支附近,震源机制解显示为近NS向拉张型破裂,与羌塘块体的主要变形特征一致。根据M—t图、频次图、能量释放、最大与次大地震震级差、b值、h值等结果进行分析,可知:①此次尼玛地震序列为一次主震—余震型序列,且余震衰减迅速;②地震发生在西藏西部地区,震中500 km范围内无地球物理观测测项,震前异常以地震活动性参数异常为主,并存在1项热红外异常;③异常均在震前半年内出现,其中热红外异常于震前一周出现。对这些异常进行详细总结,可为西藏西部地区的强震短临预报积累经验。

We systematically summarized the tectonic setting,source parameters,and sequence characteristics of the Nyima M_(S)6.6 earthquake,Tibet on July 23,2020,as well as anomalies before the rupture.The epicenter is close to the branch fault of the Yibug Caka-Rigain Pünco fault.The focal mechanism is a tensile rupture with a near NS strike and is consistent with the main deformation feature of the Qiangtang block.M-t plot,frequency diagram,energies,magnitude differences between the largest and the second-largest shock,b value,and h value were analyzed.Results show that this earthquake is a mainshock-aftershock type sequence with the rapid decay of aftershocks.The epicenter is located in west Tibet without any geophysical observations within 500 km.A few seismic activity parameter anomalies occurred within half a year before the mainshock,and a thermal infrared anomaly occurred a week ago.An elaborate summary of those anomalies would accumulate experiences for the prediction of strong earthquakes in west Tibet.