Full Wave Seismic Wave Field Numerical Simulation Based On The Layered Elastic Medium

Seismic wave field numerical simulation is a very important field of seismology technical method which abstracts the specific geological model to simplifies it to the mathematical model and gets the seismic response with numerical calculation method at the meantime. The target of the seismic wave field numerical simulation is getting the theories deep relations and the time slice by calculation in known underground geological characteristics. Seismic wave field numerical simulation plays a great supporting role in seismic data acquisition, processing and interpretation of seismic data.The main method of seismic wave field numerical simulation includes two categories:the wave equation method and the ray tracing method. The wave equation method is essentially solve the seismic wave equation numerical simulation, the simulation of seismic wave field contains all information of seismic wave propagation. The ray tracing method is to simplify the seismic wave theory for the ray theory which main consideration is the kinematics characteristics of seismic wave propagation.The traditional method of ray tracing is to solving the problem of the P wave ray path and its corresponding travel time. But this method has no consideration of the attenuation of seismic wave field and converted waves. Compared with the wave equation numerical simulation method, the method of ray tracing has a higher speed without any dynamic information of the seismic wave field. In this thesis, the ray tracing method was chosen in the wave field simulation. At the meantime the attenuation information and the ray tracing of converted waves are added to make up the defects of ray tracing method on dynamics.This thesis mainly studies the layered elastic medium model, mainly considering the two aspects of attenuation:transmission loss and spherical diffusion. In the aspect of transmission loss, the Zoeppritz equation is cited to calculate the reflection coefficient and transmission coefficient; in the aspect of spherical surface, the thesis derived the spherical diffusion factor combined with horizontal layered medium.In terms of ray tracing, this thesis completes the traditional P wave ray tracing with bending shooting method and iteration method. Considering the P wave and SV wave will produce the converted wave under the condition of non-normal incidence, each of the non-normal incidence ray has calculated the transmission P wave, reflection P wave and transmission S wave and reflection S wave which is the full wave ray tracing. Full wave ray tracing improves the traditional ray tracing algorithm, mixes the shooting method and iteration method to determine the ray incident point. It also tracks similar wave and converted wave at the same time,-introduced the’quaternary tree’data management for all kinds of waves and enriches the type of track wave.In the process of full wave ray tracing, when the ray path tracing and travel time calculation is calculating, matching the reflection coefficient transmission coefficient and the spherical diffusion factor to the ray of each layer to complete its energy attenuation. Due to during the track of converted wave, also finished for tracking multiple wave, so the synthetic seismogram covers the P wave and shear wave information, similar wave and converted wave information, primary wave and multiple wave information. So the relatively complete synthetic seismogram is obtained in higher computing speed. The model calculation proves the full wave ray tracing achieves good results.