震源顶部条件-前兆优显层的讨论

在地震预报工作中,人们既期望直接观测到震源地方的情况,又期望观测手段易于实施以及干扰因素较小。但是这几个方面是不易得兼的。例如为了直接观测震源地方的情况,则探测深度就要深,此时测量手段不易实施;如观测震源在地表的间接表现,虽手段易于实

ON THE CONDITION OF THE EARTHQUAKE SOURCE TOP-THE PRECURSOR ADVANTAGEOUS LAYER

In the earthquake prediction.people not only expect to observe direct-ly the change of source,but also to do the practice of observational method much easier.At the same time one requires the disturbance factors are small.This paper discussed the top case of shallow great earthquake.According to practical data,the information of precursors is very obvious in this depth It is an advantageous layer for observing precursors.Because the source of shallow great earthquake is located in the granite layer,the top of source is between the bottom of deposit layer and the top of granite layer,about 4-8 kilometers from surface.In such depth,the confining pressure is low,therefore,the dilatancy,the stable sliding on source fault plane and the fluid move preceding great earthquake are very obvious,but the disturbance from earth surface is not large in this depth.On the other hand,an anomaly low resistivity layer,which contains much water with high temperature and certain pressure exist between the granite layer and deposit layer.In some places of the layer the fluid is in a superheat state-an unstable state,when some changes from the source arrive there,the superheat fluid will explode.Thus it will lead to the amplification of the message from the source and to sudden change of precusor.Therefore,we call it precusor abvantageous layer.In future,it is very important to put the instrument of observation in such a layer for measuring the message from the source.