In this paper, the mechanism of tectonic earthquake is discussed qualitatively, and the sequence of Tangshan earthquake is simulated with aid of computer. On the basis of this, a group of mechanical parameters and some qualitative understanding for the deeply buried rocks is gained.
Since the deeply buried rock is the direct object of earthquake occurrence, it is certainly significant to get a clear understanding of mechanical behavior of deeply buried rocks for the study on the mechanism of earthquake forming, generating and the long term prediction of earthquakes. But as things are, although researches have been done a great deal of rock experiments; and obtained mechanical parameters under various forcing condition rock specimens used in experiment were mostly from the place where were easy to sample in the upper crust. Obviously, it is not proper to apply these experimental results in deeply buried rocks. We now generally infer that the deeply buried rock is in the state of high-temperature, high-pressure and high-density. Many researchers have done experiment under similar conditions (Stesky, 1975; Byerlge, 1975; Engelder, 1975). But how to apply their results into the actual situation is a problem pending further study in itself. However, from their studies, we gained a good deal of enlightenment and experimental basis. It is well known that the earthquake carry a great number of information, we may take it as an information source, and try to re-appear the forming and generating procedure of occured earthquakes with the theory of seismology and morden mechanics. By this, quantitatively and qualitatively, we will gain some mechanical parameters and properties of deeply buried rocks.
It is well known that the earth is always in moving, consequently, there is force in the crust. When the force, whose magnitude and orientation are different with the space and the time, act on the rock layer which makes up the crust, the crust certainly will deform, such as fracture, fold, ascent or descent of land and large scale magmatism, meanwhile, earthquake is caused. This kind of earthquakes is called tectonic earthquake, it is the most common in the crust, and the majority of shallow focus earthquake (h≤ 70km) belong to this kind, which are often destructive shocks. The tectonic earthquake usually occur at or near the fault terminus or at the locking area. Because of the inhomogeneity of rocks, the displacement and stress field are always in adjusting, it result that around the rocking area or the fault turminus stress will concentrate to a high degree, and a great deal of elastic energy will be accumulated. When the stress level exceeds the locking strength or the frictional stress, the dislocation along the fault plane will be caused, the accumulated strain energy will be suddenly released and the static frictional stress on the dislocation surface may drop considerably at the time of rupture because of the loss of cohesion.
