2017年四川九寨沟7.0级地震前地震应变场分析

Research on the Seismic Strain Field prior to the 2017 Jiuzhaigou, Sichuan MS7.0 Earthquake

摘要:

以地震应变场作为地震活动的变量，通过自然正交函数展开方法，计算2017年8月8日四川九寨沟7.0级地震前的地震应变场，提取出震前时间因子的异常变化。计算结果发现应变场前4个时间因子在震前1~3年的中短期异常并不显著，只有第2个和第4个时间因子震前有小幅度的异常变化，分析其原因，时间因子可能受到2008年汶川8.0级地震和2013年岷县漳县6.6级地震前大幅度异常的影响。与时间因子对应的空间等值线形成局部应变高值异常危险区，可能是2013年岷县漳县6.6级地震和2017年九寨沟7.0级地震空间异常的中短期特征。再对比九寨沟7.0级地震前后与松潘-平武7.2级双震的空间异常随时间演变，分析异常发展变化模式的差异，最后应用地震资料的累积频次从物理角度解释异常形成的机制。

Abstract:

In this study, we used the seismic strain field as a variable indicating seismic activity. Using natural orthogonal function expansion, we calculated the seismic strain field prior to the Jiuzhaigou, Sichuan M_S7.0 earthquake on August 8, 2017, and extracted anomalous variations in the time factor prior to the earthquake. The calculation results show no obvious mediumor short-term anomalies in the first four time factors of the strain field in the period 1-3 years before the earthquake, with abnormal changes of small amplitude occurring only in the second and fourth time factors before the earthquake. The time factors may be affected by the large amplitude anomalies occurring prior to the 2008 Wenchuan M_S8.0 earthquake and the 2013 Minxian-Zhangxian M_S6.6 earthquake. The spatial contours that correspond with the time factors indicate a dangerous area in the local strain's high value anomaly, which may be medium-and short-term characteristics of the spatial anomalies of the Minxian-Zhangxian M_S6.6 and Jiuzhaigou M_S7.0 earthquakes. Next, we compare the evolution of the spatial anomalies with time before and after the Jiuzhaigou M_S7.0 and two Songpan-Pingwu M_S7.2 earthquakes, and analyze the differences in their abnormal development patterns. Lastly, we describe the mechanism of anomaly formation from the physical perspective by applying the cumulated frequencies of the seismic data.