2015年昌黎MS 4.2地震发生前易县地震台钻孔应变观测数据异常

2015年9月14日河北昌黎发生M_S 4.2地震，收集整理易县地震台四分量钻孔应变仪观测数据，基于面应变和切应变视角进行分析，发现二者在震前出现异常变化，且2组面应变相关系数在震前数天即出现异常，该异常或可作为中小地震前应力应变异常识别的信息之一。

Anomaly analysis of borehole strain observation data of Yixian Seismic Station before Changli MS 4.2 earthquake in 2015

On September 14, 2015, an M_S 4.2 earthquake occurred in Changli, Hebei Province. The observation data of the four-component borehole strain gauge at Yixian Seismic Station were collected and analyzed from the aspects of surface strain and shear strain. It was found that they had abnormal changes before the earthquake, and the two groups of surface strain correlation coefficients showed anomalies several days before the earthquake. This anomaly may be one of the information for identifying stress-strain anomalies before small and medium earthquakes.