Calculation Of The Ground Motion Caused By A Finite Source In Stratified Media

At first, the fundamental theories of the seismic wave propagation in stratified media, the basic principles of calculating ground motion caused by a point source using the method of generalized reflection and transmission matrices, and several classical technical problems in calculation as well as their typical solutions to those problems are learned. Then, on the basis of the fundamental theory of seismic wave calculation in stratified media, with consideration of arbitrary geometry and tempo-spatially variable focal mechanisms of finite sources, as well as development trend of parallel computation, and with reference to the programs already developed for calculating point-source-caused ground motion, using Matlab programming language with great advantages of matrix computing and data visualization, this paper focuses on improvement of computing-flow in the point-source case and development of a new program to be suitable for both point sources and finite sources with arbitrary geometries and tempo-spatially variable mechanisms.With Consideration of characteristics of the distribution of finite sources in depth direction, the same single-loop is adopted to compute generalized reflection and transmission matrices for all the source depths, which largely raises the computing efficiency; and with consideration of the possibilities of the variation of focal mechanisms of finite sources with both time and space, source contribution of the six basic types of sources(seismic moment tensors) are pre-calculated, which also helps to raise computing efficiency.Meanwhile, in order to adapt the development trend of parallel computation, parallel computation is applied to two steps, one for calculating the extremely time-consuming generalized reflection and transmission matrices, in which generalized reflection and transmission matrices for the up-going and down-going waves are simultaneously computed; the other for summing the ground motions caused by finite source, in which the ground motions at a number of observation stations caused by the finite source are simultaneously summed.In order to investigate reliability, computing efficiency and functions of the program, enough numerical tests in cases of far field, near field, point sources and finite sources are designed, and the test results and computing time are compared with those from already developed applications. The comparison indicates that the application developed in this study is reliable, rather more efficient and applicable.At last, in order to evaluate the emergency function of the application developed in this study, the application is applied to the 2008 Wenchuan Ms8.0 earthquake and the 2010 Yushu MS7.1 earthquake. The results indicate that the application could reconstruct the image of ground motion which could well explain the spatial distribution of main disaster across the epicentral areas.