宁夏几次中强地震前的重力异常特征

CHARACTERISTICS OF GRAVITY ANOMALY BEFORE A FEW MIDDLE AND STRONG EARTHQUAKES IN NINGXIA PROVINCE

本文介绍了八十年代以来宁夏几次中强地震前的重力异常资料。识别异常的标志是,以幅值大于2mσ为依据。重力异常形态有正也有负;异常空间展布范围一般局限在距震中60km的区域内,该区出现较强的垂直差异运动,显示异常的重力测段多分布在地震烈度衰减较慢的一侧;异常持续时间约为几个月至一年半,而且近离震中区的重力测段比远离震中区的测段异常出现早,持续时间长。其中有的异常是地震前就有所察觉并据此提过内部试报意见。

The data of gravity anomaly before a few middle and strong earthquakes since 1980s in Ningxia Province are introduced.The mark of distingushing anomaly is based on the amplitude above 2moσ.The shape of gravity anomaly is both possitive and negative and the range of space distribution is located in the areas where are about 60km away from the earthquake center.There are the greater vertical difference motions in the areas.The gravimetric sectors with anomaly are mostly distributed over one side which the seismic intensity is attenuated slowly. The continuous time of anomaly is from a few months to one year,and the area near the earthquake center is earlier and longer anomaly than the area far from it. Some anomalies has been awared before earthquake and internal prediction tried on these ground.