崇明与南京台震前地电场变化异常分析

2001年11月3日和12月25日江苏南通地区分别发生了ML3.8和ML4.1的地震群事件. 本文以上海崇明地电场台和南京地电场台ZD9A大地电场仪的观测资料为研究对象，在阐述了多极距地电场观测去噪音原理的基础上, 研究了这两个台站地电场多极距观测系统的资料在震前的异常变化特征. 结果表明: ① 多极距观测去噪音方法是一种很好的识别地电场噪音的方法；② 在震前20天、2天及42天离震中较近的崇明台NS和NE方向上分别接收到了地震电信号, 其持续时间最长的为9天，而较远的南京台出现的异常信号都是噪音信号而非地震电信号；③ 地电场多极距观测系统中公用电极的布极方式是不可取的. 

STUDY ON THE VARIATION CHARACTERISTICS OF THE GEOELECTRIC FIELD PRECEDING EARTHQUAKES

Earthquake events occurred in Nantong, Jiangsu province on 3 Nov., and 25 Dec., 2001 in which the biggest magnitudes were M L3.8 and M L4.1 respectively. This paper firstly explains the principle of the eliminating noise method by the multi dipole observation system of geoelectric field. Then based on the observation data of the multi dipole observation system obtained by ZD9A telluric current monitors installed in Chongming and Nanjing stations, we study the abnormal variation of the geoelectric field preceding the earthquakes. The study shows that: a).eliminating noise method of multi dipole observation is an excellent method by which many kinds of geoelectric field noises can be eliminated successfully and the geoelectric precursor information can be recognized; b).the geoelectric precursor signals for the events were recorded on the NS and NE dipoles in Chongming station 42 days,20 days and 2 days before the earthquakes respectively, in which the station is near the epicenter, and the longest time of persisting period was 9 days. The abnormal variation signals of geoelectric field observed in Nanjing station are all the noises but not the seismic electric signals, in which the station is not near the epicenter; c). dipole distribution method of common electrode is not good in the multi dipole observation system of the geoelectric field.