HR: 10:50h
AN: NG22A-03    [Abstracts]
TI: Predicting Earthquake Occurrence at Subduction-Zone Plate Boundaries Through Advanced Computer Simulation
AU: * Matsu'ura, M
EM: matsuura@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, University of Tokyo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Hashimoto, C
EM: hashi@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, University of Tokyo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Fukuyama, E
EM: fuku@bosai.go.jp
AF: National Res. Inst. for Earth Science and Disaster Prevention, Tennodai, Tsukuba, 237-0061 Japan
AB: In general, predicting the occurrence of earthquakes is very difficult, because of the complexity of actual faults and nonlinear interaction between them. From the standpoint of earthquake prediction, however, our target is limited to the large events that completely break down a seismogenic zone. To such large events we may apply the concept of the earthquake cycle. The entire process of earthquake generation cycles generally consists of tectonic loading due to relative plate motion, quasi-static rupture nucleation, dynamic rupture propagation and stop, and restoration of fault strength. This process can be completely described by a coupled nonlinear system, which consists of an elastic/viscoelastic slip-response function that relates fault slip to shear stress change and a fault constitutive law that prescribes change in shear strength with fault slip and contact time. The shear stress and the shear strength are related with each other through boundary conditions on the fault. The driving force of this system is observed relative plate motion. The system to describe the earthquake generation cycle is conceptually quite simple. The complexity in practical modeling mainly comes from complexity in structure of the real earth. Recently, we have developed a physics-based, predictive simulation system for earthquake generation at plate boundaries in and around Japan, where the four plates of Pacific, North American, Philippine Sea and Eurasian are interacting with each other. The simulation system consists of a crust-mantle structure model, a quasi-static tectonic loading model, and a dynamic rupture propagation model. First, we constructed a realistic 3D model of plate interfaces in and around Japan by applying an inversion technique to ISC hypocenter data, and computed viscoelastic slip-response functions for this structure model. Second, we introduced the slip- and time-dependent fault constitutive law with an inherent strength-restoration mechanism as a basic equation governing the entire process of earthquake generation. Third, combining all these elements, we developed a simulation model for quasi-static stress accumulation driven by relative plate motion. Fourth, we also developed a simulation model for dynamic rupture propagation on a 3D curved plate interface by applying BIEM. Finally, to simulate the complete earthquake generation cycle, we couple these quasi-static and the dynamic models on the Earth Simulator, which is a high-performance, massively parallel processing computer system with 10 TB Memory and 40 TF peak speed. With this system, given the past slip history and the present stress state, we can predict the next step fault slip and stress changes through computer simulation. As an example of predictive simulation, we show the quasi-static process of stress accumulation at the source region of the 1968 Tokachi-oki earthquake, northeast Japan, and the subsequent dynamic process of rupture initiation, propagation and stop. In this simulation we forced dynamic rupture to start by giving an artificial stress drop, which corresponds to some external disturbance. The dynamic rupture is accelerated, if the stress state is in critical. Otherwise the started rupture is not accelerated. This indicates that the stepwise predictive simulation with the real-time data of stress states at plate interfaces is crucial for the prediction of large interplate earthquakes.
DE: 7260 Theory and modeling
DE: 8123 Dynamics, seismotectonics
DE: 7209 Earthquake dynamics and mechanics
DE: 3200 MATHEMATICAL GEOPHYSICS (New field)
SC: Nonlinear Geophysics [NG]
MN: 2004 AGU Fall Meeting