HR: 0800h
AN: S41A-0945    [Abstracts]
TI: Spontaneous Rupture Processes on a Bending Fault
AU: * Kase, Y
EM: ykase@moho.sdsu.edu
AF: Department of Geological Sciences, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-1020 United States
AU: Day, S M
EM: day@moho.sdsu.edu
AF: Department of Geological Sciences, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-1020 United States
AB: We simulated spontaneous rupture processes on vertical bending faults, using a 3-D finite-difference method. Since shear and normal stresses on the fault depend upon its angle to the principal stresses, rupture velocity and slip ahead of a bending point vary with strike change. Moreover, slip on a bending fault is less than one on a flat fault, since a bending point acts as a partial barrier to slip. In our 3-D finite-difference model, we modeled fault strike change by mapping a rectangular grid onto a parallelogram grid (Inoue, 1996). The grid interval along the fault should be uniform for calculations of spontaneous rupture processes. A hypocenter is located on the center of the optimum striking fault. Varying the bending angle, we calculate dynamic rupture processes under uniform principal stresses. When fault strike changes to promote compressional normal stress across the fault (_grestraining bend_h), rupture velocity ahead of a bending point decelerates. On the other hand, rupture velocity accelerates when a fault strike change promotes extensional normal stress (_greleasing bend_h). Rupture velocity near a free surface is especially sensitive to the shear and normal stress changes accompanying bending. The shear and normal stress variations also produce variations in the slip distribution. Slip on a fault with a releasing bend is larger than one on a fault with a restraining bend, since stress drop is higher on the areas experiencing enhanced extensional stresses than on those experiencing enhanced compressional stresses. On a flat fault, however, slip is higher than for either bending fault case. The obstruction caused by a bend lessens slip on the entire fault.
DE: 7260 Theory and modeling
DE: 8010 Fractures and faults
DE: 7200 SEISMOLOGY
DE: 7209 Earthquake dynamics and mechanics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting