Abstract: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.
