HR: 14:25h
AN: G22D-04    [PDF]
TI: Multi-cycle Dynamic Models of Thrust Faulting and Normal Faulting
AU: * Duan, B
EM: benchun@namazu.ucr.edu
AF: Department of Earth Sciences, University of California, Riverside, 900 University Avenue, Riverside, CA 92521 United States
AU: Oglesby, D D
EM: david.oglesby@ucr.edu
AF: Department of Earth Sciences, University of California, Riverside, 900 University Avenue, Riverside, CA 92521 United States
AB: Using the two-dimensional dynamic finite element method, we compare the behavior of thrust faults and normal faults over multiple earthquake cycles. The earthquake cycle is simulated by an inter-seismic loading phase and a dynamic rupture phase. The earthquake fault is loaded by a constant slip velocity at the base of the fault. The coefficient of friction drops from a static level to a sliding level over a critical slip distance during dynamic rupture, and recovers to the static level after dynamic waves die out. The transition from the loading phase to the dynamic phase can be accomplished spontaneously, rather than introducing an artificial triggering procedure. We conduct numerical simulations for faults of various dip angles. The results demonstrate that both thrust and normal faults tend to develop a stable event pattern: a large event, which ruptures the whole fault, is preceded by several small events that rupture about 1 km length of the fault, and one or more moderate events that rupture several km along the fault. During the stable event pattern, the stress evolution and slip evolution for thrust and normal faults are quite similar. However, normal faults develop a stable event pattern more rapidly than thrust faults, when they start from the same initial preset stress level. The results also demonstrate that variation of normal stress on faults plays an important role not only during the dynamic rupture phase, but also during the loading phase. The normal stress at the lower end of faults, where rupture usually starts, increases on normal faults during the loading phase, whereas it decreases on thrust faults. This variation of the normal stress during the loading phase has several important implications for the behaviors of these two fault types, given similar initial stress level and frictional properties on faults. First, normal faults take a longer time to reach the failure level than thrust faults, due to the above variation of normal stress on faults. Second, the shear stress level on the whole fault just before the onset of dynamic rupture is higher for normal faults than thrust faults, due to the longer loading time. Third, for an event that ruptures the whole fault, normal faults typically have larger slip than thrust faults, due to a larger stress drop. However, peak slip rates on thrust faults are larger than those of normal faults, possibly due to the amplifying effects of the free surface interaction.
DE: 1242 Seismic deformations (7205)
DE: 7205 Continental crust (1242)
DE: 7209 Earthquake dynamics and mechanics
DE: 7212 Earthquake ground motions and engineering
DE: 7260 Theory and modeling
SC: Geodesy [G]
MN: 2003 Fall Meeting