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1976年唐山地震前，在距震源很远的地区内都观测到一些前兆趋势变化，如重力、重力位二次徽商W△、水氧、地电阻率、水位和油井出油量等变化。作者认为这些变化不是由震源体直接引起的，而是在区域应力场的作用下，在某些活动断层附近，浅层岩，尤其是含水砂岩层和含油层受挤压出现的一些与地震有关的异常现象。其特征是：（1）异常范围大，可能在距震源很远的地方发生，但就同一种方法的多个观测点来说却又是局部的，即只有其中部分测点才能观测到异常，不少测点观测不到异常。（2）异常发生的时间大致相同。有些异常有同步变化的特征，如同时上升或同时下降。（3）临震前多数异常有恢复的趋势。这些特征与引起异常的机理有关。作者还从理论上计算了这种趋势异常量级，重力变化100×10-6cm／s2左右，重力位二次微商变化（1～2）×10－9／s2，地电阻率变化2％～3％，Rn变化7．4～11．1Bq／L，这样的变化量在活动断层附近的一些台站可能观测到。作者还研究了干旱降雨对某些前兆的影响，其影响量级可以被一些方法观测到，因此在确定是否是地震异常时，必须注意利用综合分析的方法排除干旱降雨的影响，减少异常的多解性。
Before the 1976 Tangshan earthquake, some precursory trend changes were observed in areas far away from the hypocenter, such as gravity, gravitational secondary water quotient W △, water oxygen, earth resistivity, water level and oil well oil output. The author believes that these changes are not directly caused by the source body, but rather are related to earthquakes that occur in the vicinity of some active faults under the action of the regional stress field, as a result of the extrusion of shallow rocks, especially the water-bearing sandstone and oil-bearing formations Abnormal phenomenon. The characteristics are: (1) The range of anomaly is large, it may happen far from the source, but it is partial to many observing points of the same method, that is, only some of the measuring points can observe the anomaly, A lot of measuring point observation is not unusual. (2) The time of occurrence of anomaly is about the same. Some anomalies have the characteristics of simultaneous changes, such as rising or falling simultaneously. (3) The majority of anomalies before the quake have a tendency of recovery. These features are related to the mechanism that causes abnormalities. The author also calculated the anomalous magnitude of this trend theoretically, with a change of gravity of about 100 × 10-6cm / s2, a change of second derivative of gravity (1-2) × 10-9 / s2, a change of 2% ~ 3%, and Rn varies from 7.4 ~ 11.1Bq / L. Such variation may be observed at some stations near the active fault. The authors also study the effects of drought rainfall on some precursors and the magnitude of their effects can be observed by some methods. Therefore, when determining whether an earthquake is anomalous, we must pay attention to using comprehensive analysis to eliminate the effects of drought and reduce abnormalities Solution.