1 INTRODUCTION
In the light of Theological property which crustal rocks have and some features of earthquake, a rheological model for faulted rocks is suggested in this paper, and the possibility for the suggested model's application to the study of earthquake mechanism is discussed. The results show that it is reasonable for faulted rocks to be simplified with the suggested model.
By way of long-term observation on deformation of rocks, it is discovered that rocks have rheological properties, i.e., under the action of external force, stress and strain in the rocks are constantly changing with time. In this century, researchers have done purposefully a great deal of rheological experiments of rocks, and their studies showed that this kind of time-dependent change is not disorderly and unsystematic, but regular and with inherent laws and can be well simulated by use of some empirical and theoretical models. At present, though the rheological property simulated by these idealized model are not completely coincident with the actual situations and still have somewhat difference, this kind of simple physical idealization for the rheological properties of rocks has a bright future because the one-dimensional solutions deduced based on these simple rheological models can according to some particular conditions be spreaded to the three-dimensional problems which consider the time factor, and it plays a very important part in dealing with the practical problems (Jaeger & Cook, 1976). On the other hand, since H.F Reid (1910) advanced the elastic rebound theory, which he developed on the occasion of the great San Francisco earthquake of 1906, the theory which the reactivation and the formation of a fault causes an earthquake has been generally admitted and accepted, and a great deal of results achieved on this theory. Their studies obviously have played without doubts an important part in the study of earthquake mechanism. Especially in 1970's, W.P. Brace et al. advanced the stick-slip as a mechanism of shallow-focus earthquake (h=70 Km) based, on the laboratory studies, which further perfects the theory that the reactivation of a fault causes an earthquake, and opens up a new channel for combining the study on mechanical properties of faulted rocks with the study of earthquake mechanism. Nevertheless, their theory always are confined to the qualitative description of the earthquake mechanism. In order to achieve the idea of quantitative analysis, in this paper, we start with the consideration of the visco elastoplastic properties of faulted rocks, and advanced a mathematical model and analyze its application to the study of earthquake mechanism.
Natural rock is an uncontinuous medium with elasticity, plasticity, viscosity and a large number of fissures. According to the knowledge of the origin mechanism of tectonic earth- quake, the occurrence of a great earthquake and its after- shock sequence are the repeating of such a process that firstly, strain energy accumulated in the faulted rocks or the rocks surrounding the fault and then suddenly released due to the instability of the faulted rocks, at last, stress recovered.
