2020年7月12日河北唐山5.1级地震总结

系统梳理2020年7月12日唐山古冶区5.1级地震前出现的地震活动和地球物理观测等异常，结果如下：①地震活动：震前存在地震平静、小震高频、中等地震成组等中短期异常；②地球物理观测：震前主要为电磁和流体异常，短期异常主要分布在震中100 km范围内；③震后回溯：北京及周边震前存在地震发生率异常，利用其他综合方法主要识别出年尺度异常。此次唐山5.1级地震发生在1976年唐山7.8级地震余震区，而7.8级地震序列地震活动呈非均匀衰减特征。此次唐山5.1级地震震源机制为走滑型破裂，截至7月31日，序列b值为0.70、h值为1.8，序列参数基本正常。综合分析认为，此次地震发生前，地震活动中短期异常较显著，地球物理观测异常占比明显偏低；震前对该区域出现的中期和短期异常有所察觉，但短期异常的预测强度偏低，震后总结时按震前异常预测的地震强度为4—5级，接近实际发生地震的强度。

About Tangshan MS 5.1 earthquake in Hebei on July 12, 2020

The anomalies related to the Tangshan M_S 5.1 earthquake are comprehensively sorted out. The seismic activity anomalies tracked before the earthquake consist of mid- and short-term anomalies such as seismic quiescence, high-frequency of small earthquakes, and moderate earthquakes in groups. The geophysical anomalies tracked before the earthquake are mainly electromagnetic and fluid anomalies; and the short-term anomalies are mainly located within 100 km of the epicenter. The anomalies summarized after the earthquake include the anomalies in the occurrence rate of earthquakes in and around Beijing and the annual-scale anomalies identified by some comprehensive methods. The M_S 5.1 earthquake occurred in the aftershock area of Tangshan M_S 7.8 in 1976. The sequence of the Tangshan M_S 7.8 earthquake is characterized by non-uniform attenuation. The focal mechanism of the M_S 5.1 earthquake is strike-slip rupture. Until July 31, its sequence parameters that b value is 0.78 and the h value is 1.8 are basically normal. To sum up, before the earthquake, the mid- and short-term anomalies in seismic activity are significant, and the proportion of geophysical observation anomalies is low. The mid- and short-term anomalies in the region were noticed before the earthquake, but the magnitude of the predicted earthquake is lower than that of the actual earthquake. After the earthquake, the predicted magnitude using the anomalies is around 4-5, which is closer to the actual earthquake.