摘要:
研究了地电短临震兆机理,在此基础上给出了引潮力触发地电短临前兆模式。据此从理论上分析了地电临震震兆特征,并以唐山7.8级大震为例,从实际观测中检出具有此模式特征的震兆(具有起潮力特征),从而验证了所提模式理论的客观存在的可能性。最后给出与此有关的地电短临预报方法。即,根据脆性岩石失稳的相对刚度比较准则,定义部分岩体刚度λ=0的状态为临震阶段,分析λ=0时起潮力引起位移的特征和规律,得出原地监测岩体刚度是否为零(进入临震阶段)的方法。因为在弹性阶段,λ为较大正值,微小的起潮力只引起微小的位移,此时的电响应甚小,通常检测不到;但随着构造力的积累,介质进入临震阶段,此时同样微小的起潮力却可引起甚大的位移(λ=0时,位移为无穷大),从而产生可检测的电响应。由于这种电响应具有与起潮力相同的周期,故可把临震电响应同各种干扰区分开,判定为临震前兆,从而建立了地电临震前兆起潮力触发模式,并可给出相应的短临预报方法。对1976年唐山7.8级强震前后震中周围地电阻率及大地电场实测资料进行谱分析,发现仅在主震前二个月至半月内,两种不同物理本质的电响应分别出现与起潮力MS波与MSf波周期相同的异常变化。这是对所提临震前兆模式和预报?
Abstract:
Mechanism for generation of geoelecfric precursors and a model of imperding earthquake precursorsof geoelectricity triggered by tidal forces are presented.The anomalies in both georesistivety and selfpotential measurements obtained two months before the M7.8 Tangshan earthquake of 1976 are taken as example, which have periods equal to that of the tidal forces M2 and MSf respectively, so that the reasonableness of the proposed model is proved and a new method of short-term or impending-earthquake prediction is proposed.According to the instability criteria of the stiffness (λ)comparison, the state of λ=0 is considered as the impending earthquake stage.In our model we regard the tidal force as the input signal while any field, which can directly or indirectly reflect the displacement of response is inversly proportional to the stiffness.Nomally the amplitude(A/λ) of response is always a very limited small value, which cannot be detected by our electric measurements, since λ is usually a relatively large positive constant during elestric deformation.However, the same small tidal force results in an abnormally large amplitude of theresponse, which is appoaching infinity when λ=0 and can be detectable, when an impending-earthquake stage is reached owing to sufficient accumulation of tectonic stress.The impending-earthquake response can be identified from noises according to identical and abnormally large amplitude to the tidal force and a short-term earthquake prediction can be made.
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