根据地下水资料的数字滤波探讨唐山大震的孕育过程

采用纯振幅、点阻、带通数字滤波器,处理了距唐山180公里范围内13口深井水位的大震前六年连续观测资料。结果表明,大震前存在井水水位的异常下降,这种异常下降首先发生在距大震震中100公里处,并且以每月5-6公里的速度分别向震中和离开震中的方向传播。地下水异常下降的时间-距离关系与该区里小震发生的时间-距离关系较一致。据地下水异常下降结果,我们提出唐山大震孕育过程可以分为三个阶段:1972年-1974年底,1975年-1976年4月,1976年4月-大震发生。

INVESTIGATION OF PREPARATORY PROCESS OF TANGSHAN EARTHQUAKE ACCORDING TO DIGITAL FILTERING OF THE DATA FOR UNDERGROUND WATER

The data of underground water levels from 13 deep well scattered around the epicenter about 180 km before Tangshan earthquake, are processed by use of the pure amplitude, point resistance and the band pass digital filters. The results show that there are abnormal drops of water levels in the deep wells before the main shock, and such drops appear first at the distance of about 100 km from the epicenter. Then, they were propagated with velocity of 5-6 km/month both towards and away from the epicenter. This pattern is in accord with the time and spatial distributions of the small earthquakes occurring in the same area. It was suggested that the preparatory process of Tangshan earthquake can be divided into three stages: stage Ⅰ, from Jan. 1972 to Dec. 1974; stage Ⅱ, from Jan. 1975 to Apr. 1976; stage Ⅲ, from Apr. 1976 to the occurrence of Tangshan earthquake.