3d Modeling Of Dynamic Fault Rupture And Strong Ground Motion Of The 1976 M_s 7.8 Tangshan Earthquake

Using 3D finite difference code developed by Dr. Day in SCEC, we simulated fault dynamic rupture process with associated near-fault strong ground motion for the 1976 Ms7.8 Tangshan earthquake based on a simplified bi-lateral rupture model and slip-weakening friction law. The length, width, and depth of the model are 210km, 140km, and 40km, respectively. The discredited space and time steps are 200m and 0.012s, respectively, which make the total numbers of node points up to 0.15 billion. In the implementation level, a parallel computational algorithm has been developed in DELL work station, and a computer visualization technique has been used in the numerical simulation in order to do data analysis. Furthermore, a regional 3D velocity model also has been embedded into the model to simulate seismic wave propagation and associated ground motion.According to the numerical results, we have a more explicit cognition to the process of Tangshan fault rupture and the strong ground motion. The major works and results acquired as followed:(1) We protracted the distribution of ground motion near the Tangshan fault by analyzing the simulation results. It shows that the PGA and PGV caused by the southwest of the fault is larger than the northeast of it; it is also different for the attenuation speed on the two sides of the fault, it is fast on the right side than the left side. The results also show that the PGA and PAV at the end of the fault is larger, so it may be necessary to enhance the ability to prevent earthquake for the strike-slip fault.(2) We discussed the effects on the strong ground motion caused by 3D velocity structure and rupture directivity. The non-uniform of P wave in horizontal direction results in the asymmetry of the PGA and PGV. A physics based explanation related to the rupture directivity also be proposed to show the radiated SH typed particle motion (fault-normal component) from ruptured fault have a significant influence on the near fault ground motion along the fault strike direction.(3) Based on the radiated SH wave motion and propagation caused by directivity effect, we proposed that, for the 1976 Ms7.1 Luanxian and Ms6.9 Ninghe earthquakes, a dynamic triggering mechanism related to the temporal stress variation could be play a significant role to trigger these two events. The results shows that the dynamic stress change is 2~3MPa in strike direction and 0.1~0.2MPa in thrust direction.(4) Using the existing technique to visualize the fault rupture process and strong motion characteristics which provide us an insight into the understanding of fault dynamic frictional motion in detail. The 2D and 3D pictures and animations feedback the information contained in the simulation results, which promote the application of computer technique to the seismology.