2014—2018年石家庄3次4级以上地震震前地球物理异常

Analysis of seismic geophysical anomalies before three earthquakes with M_(S)≥4 in Shijiazhuang from 2014 to 2018

2014—2018年河北共发生4级以上地震6次,系统梳理震前石家庄地球物理站网记录到的不明原因数据异常事件,分析认为:①在2014年9月6日涿鹿M_(S)4.8、2015年9月14日昌黎M_(S)4.3、2016年9月10日唐山M_(S)4.2地震前,记录到的黄骅冀19井观测站、河间冀17井水位不明原因数据异常事件为地球物理异常;②黄骅冀19井观测站、河间冀17井观测站水位异常变化形态均为震前同步出现1次或多次大幅度上升型阶变,恢复正常变化形态2—3个月后发震;③对水位异常变化机理进行探究,认为黄骅冀19井观测站、河间冀17井观测站所处区域地质构造的不均匀性和水位观测的高灵敏性是记录到震前异常的主要原因,在地震孕育过程中,孕震岩体应力、应变的微小变化通过断裂带传播到观测井含水层,引起含水层岩体孔隙度改变,进而导致井筒与含水层之间水量交换,因这2口井的井孔—含水层系统导水性能良好,对地壳岩体的微小应变产生放大作用,所以井水位在地震前出现大幅度阶变;④将3级以上地震M—t图与不明信号频度(次/月)进行对比发现,当连续4个月频繁记录到不明原因数据异常事件后,将出现一个地震多发时段。

Six earthquakes with M_(S)≥4 occurred in Hebei Province from 2014 to 2018.The data anomalies recorded by the Shijiazhuang geophysical station network before the earthquakes were systematically analyzed,and we concluded that:①The data anomalies recorded at the Huanghua Well and Hejian Well before the Zhuolu M_(S) 4.8 earthquake on September 6,2014,the Changli M_(S) 4.3 earthquake on September 14,2015,and the Tangshan M_(S) 4.2 earthquake on September 10,2016 were confirmed as geophysical anomalies;②The abnormal changes of water level in Huanghua Well and Hejian Well are synchronized with one or more large ascending step changes before the earthquakes,and the earthquakes occurred 2 to 3 months after recovering tonormal;③After analyzing the mechanisms of abnormal change of water level,we believe that the main reasons for recording preearthquake anomalies are non-uniformity of geological structure and high sensitivity of water level observation in the regions of Huanghua Well and Hejian Well.During earthquake preparation,the slight changes in stress and strain of seismogenic rock mass propagate to the aquifer of the observation well through the fracture zone,causing changes in the porosity of the aquifer rock mass.This yields in water exchange between the wellbore and the aquifer.Due to the good water conduction performance of the borehole and aquifer system of these two wells,the micro-strain of crustal rock mass is amplified,so the water level has a large step change before the earthquakes;④A timeaxis comparison between the M-t map of earthquakes with M_(S)≥3 and the frequency of unknown signals(times/month)shows that when unexplained data anomalies are frequently recorded for 4 consecutive months,there would be a multi-seismic period.