【摘要】 分析了在2004年12月26日印尼8.7级地震前河北昌黎台记录到的自然电位及电场异常,结果显示昌黎台自电位、电场正常时段观测到的半日、半月潮汐波周期变化在震前1个多月发生畸变,周期消失,变化幅度相应减小,震后快速恢复,且潮汐波记录比震前正常时段更加清晰。该台地电阻率的观测结果显示起始下降变化比较平缓,震前一周左右,变化加剧,出现多次阶变。究其原因,在强震发生前断层的蠕滑作用导致孔隙压力变化,产生一种可以在岩石中传播的应变波,由于台站下方岩土层对小应变信号具有很好的放大作用,所以记录到了这种小幅度的应变波,也就是远场的静态应变效应。随着地震临近,应力作用加强,远程应变波引起台站下方水位、水化学性质以及岩石孔隙度、渗透率等的改变,导致电阻率、电场大幅度的阶变,这反映了远场应变波的动态效应。当然就异常幅度而言,应变波的效应还嫌弱一些,因此昌黎台异常变化可能还叠加了震源区激发的电磁波。更多还原

【Abstract】 In this paper,self-potential and geoelectric field anomalies were analyzed,which were recorded at Changli station of Hebei province before M8.7 Earthquake in Indonesia on Dec.26,2006.The results show that the half-daily and half-monthly tidal wave periodicity changed abnormally about one month before the earthquake,with periodicity disappearing and amplitude reducing,but they recovered after it with clearer state than that at normal time.The observation data of earth resistivity at this station exhibits that it dropped slowly at the beginning,but changed intensely in one week before the earthquake with many times of step-variations.It is found that the formation mechanism might be as follows: the creep-sliding of faults before the strong earthquakes caused local variation of pore pressure,which produced a kind of strain wave propagating in the rock and overlapped with tidal waves,then disturbing the normal records at stations.Due to the better amplification in rock and soil layer beneath Changli station for small stress and strain signals,this wave with small amplitude,i.e.the remote static strain wave,can be recorded here.With the impending of the earthquake and strengthened stress,the remote strain waves resulted in the change beneath the station such as water level,water chemical property and rock porosity,permeability and so on,leading to the large amplitude step-variation in resistivity and geoelectric field,which reflect the dynamic effects of remote strain waves.Of course,the anomaly amplitude of resistivity,the effects of stress wave is not enough,so there may be overlapped anomalous electromagnetic wave from focal area on the electric anomalies recorded at Changli station.更多还原