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1976年唐山强震发生在我国地电阻率、地磁观测、精密水准重复测量等多种观测网分布较密的地区,附近渤海沿岸还有数个长期记录的验潮站。震前地电阻率和地磁二种物理量出现了地理范围基本吻合、分布广阔的异常区。根据自然条件下岩(土)层压缩时电阻率变化的实验结果,认为只在1973～1976年间才出现的地电阻率区域下降,系地表浅层压密的结果,其压缩线应变的数量级约为3×10~(-5)。有意义的是基本在此同一区域内,1975～1976年间还观测到ΔZ和ΔF减小的效应。根据航空磁测测区内磁性地质体埋藏较深的资料及非线性压磁的实验,得知震前ΔZ、ΔF以及磁倾角减小的效应,系埋深8～25公里的磁性体非弹性体积膨胀的结果。震前精密水准测量发现,自1969年以来震中地区地面下沉,平均海平面资料表明,此下沉一直持续至地震发生。宁河(Δ=50公里)附近下沉幅度最大,可达8～12厘米。综合震前出现浅层压缩、深层膨胀、地表下沉的现象,推论唐山震前震中区附近的上部地壳(0～25公里)发生了向针弯曲现象——一种活动褶皱。唐山地震的孕育及发生便可能与此活动褶皱不断增加其挠度以致破裂有关。
The 1976 Tangshan strong earthquakes occurred in areas with densely distributed observation networks such as geo-resistivity, geomagnetic observation, and precision leveling repeated measurements. There were also several long-term recorded tidal flats along the coast of Bohai Sea. Before the earthquake, resistivity and geomagnetic two kinds of physical quantities appeared basically consistent with the geographical range, a wide distribution of abnormal areas. According to the experimental results of the resistivity change of rock (earth) layers under natural conditions, it is considered that the area of resistivity decreased only from 1973 to 1976, which is the result of the superficial compaction of the earth’s surface. Is 3 × 10 ~ (-5). It is significant that within this same area, the effects of a decrease in ΔZ and ΔF were also observed between 1975 and 1976. According to the data of deep buried magnetic geologic bodies in aviation magnetic survey area and the experiment of nonlinear compressive magnetization, the effects of ΔZ, ΔF and reduction of magnetic dip angle before earthquake are known, and the inelasticities of magnetic body with depth of 8 ~ 25 km The result of volume expansion. Precise leveling measurements before the earthquake found that the surface subsidence and the mean sea level data since the epicenter of the epicenter in 1969 show that the sinking lasted until the earthquake occurred. Ninghe (Δ = 50 km) sinking the largest amplitude, up to 8 to 12 cm. Comparing the phenomena of superficial compression, deep expansion and surface subsidence before the earthquake, it is deduced that the bending of the needle (a kind of active folds) occurred in the upper crust (0 ~ 25 km) near the epicenter of Tangshan earthquake. The occurrence and occurrence of the Tangshan earthquake may be related to the increase of its deflection and rupture caused by this active fold.