Artificial Source And Random Source Excitation Of Seismic Waves In The Finite Difference Time Domain Simulation Studies

Numerical simulation technique is one of the most effective methods in understanding seismic wave propagation in complex media. It can be used in all steps in assisting seismic surveys for a variety of purposes, from survey design, all the way to the final stage of result interpretation. With the development of the seismic wave theory and the computer technology, numerical simulation using full-wave approaches such as finite difference, finite element, pesudospectral and integral equation methods have gained wide applications in many scientific and engineering fields.In general, based on the consideration of memory usage, accuracy, efficiency and parallel computation, the staggered grid finite difference method is reputed as one of the best methods. In this paper, the finite difference time domain (FDTD) method is used to discuss the characteristics of the seismic wave triggered by the artificial explosive and airgun sources and the random ambient noise and microtremors. The simulation results can provide a reference model for characterizing underground objects'distribution and material properties with the artificial quasipoint source sounding. It can also be used to study the seismic response caused by the static/quasi-static wave field due to random microtremor vibrations.FDTD technique models wave propagation in a finite domain, which is only a truncated portion of the real world. The absorbing boundary conditions are applied to absorb the unwanted reflection from the artificial truncation boundaries. In this thesis, the perfectly matched layer (PML) absorbing boundary condition using stretched coordinate function is adapted and implemented. The simulated results of the modeling cases discussed in this thesis have approved the superior stabilities and efficiencies of this algorithm.Based on the field seismic data acquired from the Anxin-Kuancheng deep seismic sounding profile and the inversion result of the crustal structure obtained from the research of the Shang Guan Lake reservoir underground structure using explosive and airgun sources, the simulated seismic waveforms are obtained with the finite difference time domain (FDTD) method. The simulation results match the recorded waveforms quite well in all main phases. The results are also compared with wave fields using traditional approaches. These results illustrated that FDTD method is highly effective and robust in simulating seismic wave propagation in complex tectionic structures.FDTD seismic wave simulations are also conduted for understanding the interaction of microtremor with 5 kinds of fundamental structures: they are horizontal layers, inclined layers, vertical fault, normal fault and reverse fault. The results match the inversion obtained from the H/V spectral contrast method (Nakamura method) very well, which means the FDTD method can also be a good simulation method to obtain the wave field information generated by random sources, and can provide valuable scientific insight for microtremor applications in earthquake engineering studies.