Computational Simulation On Geodynamic Problems

The dynamic process of stress transmition in crust is studied by three dimensional dynamic FEM based on geophysical observation. The response of crust to ocean tide, simulation of seismogram, the globe model, the relation between geological structures and its influences to the crust stress are studied. Besed on the last two contents, the mechanism of earthquake triggering is studied. Furthermore, the feedback relation between the structure and the stress' evolution has been studied. The studies give an interpretation to those dynamic effects in crust. Analysis says that the joint research of computational mechanics and geophysical observation is acceptable.The creations in this dissertation are on four aspects.Firstly, we conduct a joint research combined computational mechanics and geophysical observations. This joint research is realistic because the dynamic FEM meets the request of geophysics research where many equation of movtion can not be expressed briefly. Therefore the three dimensional finite elemental dynamic analysis offers a way for simulating the mechanical waves in crust. In addition, by applying the nonlinear analysis to geophysics research, the physics in geodynamic process can be understood.Second, we simulate large scale geophysical objects with the full size and dynamic analysises applys to geophysical research. Usually, geophysics studies large scale object via small experimental samples. Anyhow, to extrapolate the experimental results is not always safe. In this paper, we directly study full scale model. All the research contents, include the response of crust to ocean tide, simulated seismogram, the globe model, earthquake triggering mechanism, are conducted by full scale model.Third, the concept of "simulating seismogram" is proposed as a successor of theoretical seismogram that is an inversive method. The new concept includes a material definition of media and a transmition process of waves. The S and P waves can not be distinguished from each other in a small experimental sample, save the real rarth's crust. By simulation of seismogram, we study the S and P wave in a model and comparing to the seismological observation. With the full scale model, the S and P waves are identified and successfully shown some information of the source. This is one of the meanings of simulation seismogram. Generally, any kind of theoretical seismogram, include simulated seismologram, is for getting information from the source or the media of waves by trial-and-error method.Finally, the dynamic mechanism of earthquake triggering is studied. The seismic waves are the propagations of the vibrations in crust, in which include the propagations of dynamic stresses. The compressive wave can be turned into tensile wave when it reflected on a free surface. However, the tensile or compressive wave may reduce or increase the inviromental stress in deep crust. It infuences the inner friction and, in turn, changes the Coulomb's equvlent stress. By this way, it may trigger an small rupture. As the rupture of rock will emit the seismic wave, the dynamic stress and the events of rupture form a loop of positive feedback. The positive feedback process, namely, will finally build a big event of rock rupture, that is, earthquake. The study begins with the phenomenon of rupture under an impact load. And the effect of tensile wave is researched. Taking the giant ambient stress into consideration, though the tensile stress of impact load can cause a rupture under common condition near the earth's surface, the tensile in deep crust cannot break the rock. Therefore, the mechanism of inner friction and of the coulombs' stress is proposed. Based on the train of thoughts above, we interpret the earthquake as a result of a positive feedback process when the inner friction declines and the crannies enrich and big deformation appears. This explanation matches well to the phenomenon that a big shock occurrence often accompanying a long period's normal stress decline and an obvious located deformation. By this train of thoughts, we have given a full description for earthquake triggering in dynamic mechanism.