强震前的地磁异常现象

震前地磁Z分量的日变化异常主要表现在幅度和相位上的变化,文中利用我国50多个地磁台多年的资料,重点研究了1997年11月8日玛尼7.5级地震和2005年11月26日江西九江5.7级地震。发现玛尼地震和九江地震以及大多数中强地震前,全国地磁台站地磁Z分量日变化幅度的极小值出现时间(低点时间)在空间分布上异常特征,即低点位移现象。这种少见的异常现象与强震发生有较好的相关性。发震日期为异常日后的第27天或第41天的前后4天,强震发生地区在低点位移突变分界线附近。结果显示,在玛尼7.5级地震和江西九江5.7级临震前,震中周围出现区域性Z分量日变化幅度异常现象。

The anomalous phenomenon of geomagnetism before strong earthquake occurrence

The pre-seismic anomalous daily variation of geomagnetic field in the Z-component is mainly expressed as phase change as well as amplitude variation.On the basis of the data recorded for many years by china geomagnetic network,Mani M_S7.5 earthquake on Dec.8,1997 and Jiujiang M_S5.7 earthquake on Dec.26,2005 have been especially studied.We find that the spatial distribution of the appearance time of the minima(the low-point time) of the geomagnetic vertical component appears anomalous(i.e.,phenomenon of low-point displacement) features before Mani earthquake,Jiujiang earthquake and most strong earthquakes.It has been found that most earthquakes occur in the vicinity of the boundary line of sudden change of the low-point displacement and generally within four days before and after the 27th or 41st day counting from the day of appearance of the anomaly.The anomalies of diurnal-variation amplitude near the epicentral area have been also studied before Mani M_S7.5 earthquake and Jiujiang M_S5.7 earthquake.