天山中段2次6级地震前钻孔应变高频异常分析

High-frequency anomalies of borehole strain before two MS6.0 earthquakes in the middle section of Tianshan Mountains

摘要:

2014年以来,天山中段分量钻孔应变仪空前增多,这些高采样率的应变观测资料蕴含着丰富的构造信息。如何从高采样率观测资料中提取有效的前兆异常信息,是分析研究人员亟待解决的问题。文章通过对天山中段分量钻孔应变观测数据进行S变换和超限率分析发现,在天山中段2次6级地震前有5套应变资料出现高频信息异常。这些异常均在震前出现,随后达到峰值,临震前或地震后衰减,其中短周期异常信号主要集中在10~720 min频段,且S变换与超限率分析结果具有很好的同步性。结合精河地震震源区及附近的GPS分析结果,发现高频异常信息的分布与该地区地壳运动场具有很好的一致性,进一步验证了高频信息异常的可信度。

Abstract:

Since 2014, the number of component borehole strainmeters in the middle section of the Tianshan Mountains has enormously increased. The high-sampling rate strain data contain significant tectonic information. The extraction of useful earthquake preliminary information from these data has become a top priority. We employ the S-transform and the overrun rate method to analyze the data obtained from eight sets of component borehole strainmeters in the middle part of Tianshan before two M_S6.0 earthquakes. The strain data obtained from five strainmeters provide information on high-frequency anomalies before two M_S6.0 earthquakes; these anomalies gradually increase before the earthquakes, then reach their peak values, and finally disappear before or after the earthquakes. The short-term abnormal signals are mainly concentrated in the 10-720 min frequency band. The S-transform and overrun rate analysis results are in good agreement. Combined with the GPS analysis results of the Jinghe earthquake source area and its vicinity, we observe that the distribution of high-frequency anomalies is in good agreement with the crustal movement field in this area. This indicates that the high-frequency anomalies extracted from the S-transform and overrun rate analysis are credible and can be used as a reference for earthquake case studies of strain observation data.