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在距唐山地震震源约百公里的大港油田,以水压致裂法,在深度1000—4000米之间,测定了69次地应力值,对比了1973—1980年大地震前后八年内的应力值变化。在主震前,构造应力场出现明显变化:(1)水平应力梯度降低,即在最大与最小水平主应力方向呈现应力松弛;(2)水平应力与深度的相关系数降低,即构造应力场受到扰动;(3)断层滑动系数增高,断层出现无震蠕动。此外,结合地质构造与应力测量结果,对唐山地震发生过程中的一些异常现象,如无震蠕动、地下水位变化、浅层和外围地区的应力松弛,以及应力沿断层面向深层和闭锁区的转移等,进行了分析和讨论。
In Dagang Oilfield, about 100 kilometers away from the Tangshan earthquake source, we measured 69 in-situ stress values between 1000 and 4000 meters with hydraulic fracturing method, and compared the stress values within eight years before and after the 1973-1980 earthquake Variety. Before the main shock, the tectonic stress field changed obviously: (1) the horizontal stress gradient decreased, that is, the stress relaxation appeared in the direction of the maximum and minimum principal stress; (2) the correlation coefficient between horizontal stress and depth decreased, that is, the tectonic stress field was affected Disturbance; (3) fault slip coefficient increases, there is no earthquake creep fault. In addition, combined with the geological structure and stress measurement results, some anomalies in the Tangshan earthquake such as no-motion creep, groundwater level changes, stress relaxation in the shallow and peripheral regions, and stress transfer along the faults to deep and locked regions Etc., carried out analysis and discussion.