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1976年唐山7.8级地震的临震前和主震后的一段时间内(即7月12日至10月15日),位于震中区的昌黎台,断续记录到一系列(共31个)形变电阻率值下降(负)的脉冲。其中的9个负脉冲断续出现在主震前半月之内,它们叠加在震前连续加速下降的形变电阻率背景值之上,构成一种特定的异常形态。该台自1969年观测以来,首次记录到这种现象。 这些形变电阻率脉冲的主要特征有:脉冲幅度超过平时观测标准误差3—20倍;脉冲形态均为低于趋势背景值的负脉冲;每个脉冲的持续时间较长,约达13个小时左右;脉冲极小值时刻逐日后延,每日延迟的时间与引潮力极值每日延迟的时间一致。这表明形变电阻率负脉冲与引潮力在成因上有联系。同时还发现唐山地震系列中的一些较强地震的发震时刻也与引潮力密切相关。认为形变电阻率负脉冲的出现,是震源介质力学性质在临震阶段发生变化的一种表现。
A series of 31 deformations were recorded intermittently in Changli station located in the epicenter area during the period before the Tangshan earthquake of magnitude 7.8 in 1976 and some time after the main shock (July 12 to October 15) Resistivity value drops (negative) pulse. Among them, nine negative pulses intermittently appeared in the first half of the main shock, which superimposed on the background value of the resistivity of the resistive continuous descent before the earthquake to form a specific abnormal morphology. The station recorded for the first time since its observation in 1969. The main characteristics of these deformation resistivity pulses are: the pulse amplitude exceeds normal observation standard error by 3-20 times; the pulse shape is negative pulse below the trend background value; the duration of each pulse lasts for about 13 hours ; The pulse minimum time is postponed daily, and the daily delay time is consistent with the daily delay time of extreme tide force. This indicates that the negative resistance of deformation resistivity is intrinsically related to the tidal force. At the same time, it is also found that the seismogenic moments of some strong earthquakes in the Tangshan earthquake series are also closely related to the tidal force. It is considered that the appearance of negative pulse of deformation resistivity is a manifestation of the change of mechanical properties of seismic source during the epicenter phase.