Strong Ground Motion Simulation By Finite Difference Method

Seismic wave propagation simulation in3D media is crucial in evaluating failure process of strong ground motion and estimating the damage of earthquake disaster. Finite difference method has been widely used in conventional strong ground motion simulation due to its accuracy and efficiency. In this paper, we apply curved mesh finite difference method to simulate strong ground motion process.A deadly earthquake that measured at Ms8.0jolted Wenchuan county, Sichuan province on May12th2008, more than60,000people died and4.8million people were homeless in the earthquake. It is the strongest earthquake in China since1950, the disaster area is over100,000km2, and causes tremendous economic loss. As the Wenchuan earthquake occurred along Longmenshan fault, a thrust structure along the edge of east Qinghai-Tibet Plateau and Sichuan Basin, the complex geology structure and rugged topography strongly influenced the seismic disaster distribution. Accurately simulating strong ground motion of the Wenchuan earthquake is of great significance in studying the earthquake’s source rupture dynamic process, disaster factors, and guiding the post-disaster reconstruction.In this thesis, we also simulate the strong ground motion process of Sanhe-Pinggu earthquake in Beijing, Lushan earthquake on April20th2013and Nantou earthquake on June2nd2013, and analyze the seismic wave propagation process and strong ground motion distribution of these four seismic events.Near field directivity effect, hanging wall effect, basin effect and topography effect strongly influence the ground peak value distribution in large earthquakes. Characteristics of Wenchuan earthquake are mainly affected by fault’s geometry feature, rupture pattern and basin amplification effect in sedimentary deposit of Sichuan basin, while some secondary disasters such as mountain landslides are primarily caused by topography effect. Peak ground motion distribution of Lushan earthquake is mainly caused by hanging wall effect, and topography amplifycation effect leads to much more severe calamities in Baoxing area. As the rupture of Nantou earthquake is located beneath the central range in Taiwan, topography effect is significant in that area, and the subsurface low velocity region results in stronger hazard. In the simulation of Sanhe-Pinggu earthquake, near field directivity effect, hanging wall effect and basin amplification effect all contribute to the peak ground motion distribution.From studies on the simulation of the four earthquakes, we can conclude that peak velocity along rupture direction is much larger than that deviate from rupture orientation; both value and region of peak velocity on the hanging wall are larger than that on the foot wall; thick sedimentary deposit leads to significant amplification effect, while shallow sedimentary layer has little effect on amplitude of seismic wave; amplification factor is much larger nearby the rupture, and it also increases with height of the mountains.