长江三角洲地区地磁短周期变化异常的描述及解释

THE DESCRIPTION AND INTERPRETATION OF THE ANOMALY OF GEOMAGNETIC SHORT PERIOD VARIATION IN THE REGION OF YANTZE RIVER DELTA

在长江三角洲地区进行了地磁短周期变化的观测，对资料的分析表明，该区域地磁短周期变化存在一非对称异常．其负异常较大，中心位于无锡、常熟一带；其正异常较小，中心位于海安与大丰之间．异常出现的周期为１００—３６００ｓ，并在１２０ｓ处取极大值．二维模型拟合表明，在该地区存在一由北向南上升的地下高导层．该高导层在溧阳、无锡、余山一线消失．这恰是溧阳、崇明大断裂之所在．该地区地表还存在有厚度为３００ｍ的高导覆盖层．

The observation of geomagnetic short period variation had been carried out in the region of Yantze River delta. The analysis of observation data showes that there is a unsymmetrical anomaly of geomagnetic short period variation in the region.The negative anomaly is bigger, its centre is in the area of Wuxi and Changshu.The positive anomaly is smaller,its centre is between Haian and Dafeng.The periods in which the anomaly exists are from 100 sec to 3600 sec. The maximum of the anomaly is in the point of 120 sec. 2-Dimensional modelling showes that there is a high conductivity layer undergroung in the region. The layer rises from Dafeng toward south and vanishes somewhere about Liyang, Wuxi and Sheshan where just is the position of Liyang-Chongming fracture. There also is a high conductivity overburden which thickness is 300m in the region.