远震前的地电场潮汐波异常

TIDAL WAVE ANOMALIES OF GEOELECTRICAL FIELD BEFORE REMOTE EARTHQUAKES

分析了5次远强震前河北省昌黎台、兴济台记录到的电场异常,发现该异常主要集中在震前2个月左右的时段内,具有很好的短临预报意义.震前电场呈现不同的异常特征,但与固体地球潮汐波变化关系密切,如半日、半月等潮汐波周期信号增强,引起电场变化幅度增大;或本该正常记录到的潮汐变化幅度突然减小或消失;以及高频信号增多并伴有跃变现象.分析异常产生机理认为,强震前的这种异常现象是震源区临震孕育过程中岩石弱化产生的电场异常,经自由空间或地壳传播到达地电台站后,与台站记录的电场潮汐波相叠加产生潮汐波增强或减弱现象.高频异常可能与台站下方岩石孔隙度、渗透率等介质性质的改变有关,反映了强震的远场动态效应.

In this paper, geoelectrical field anomalies at Changli and Xingji station in Hebei Province were analyzed before five remote earthquakes. It was found that the anomalies mainly occurred two or three months before earthquakes, which is of importance to shortterm and impendent earthquake prediction. There exhibited different characteristics in geoelectrical field anomalies, but they were closely related to tidal waves, for example, the increasing in amplitude at semidiurnal and semimonthly periods of tidal waves; the decreasing or disappearing in amplitude of tidal waves that should have been recorded normally at that time; while there accompanied incremental signals with high frequency, such as jump variations. It was thought that the formation mechanism of the geoelectrical anomalies before strong earthquakes resulted from stress-strain resonance effects when rock was weakened during the preparation process in seismic area, and then signals of electric field propagated to remote stations in free space or crust, and superposed on the geoelectric field tidal waves recorded at the stations, leading to increasing or decreasing in ampli- tude of geoelectrical tidal waves. The high frequency signals may be related to the variation of rock porosity, permeability and so on beneath the stations, as a result of the dynamic effects of remote earthquakes.