Investigation of Shallow Crustal Weak Zone Effects on Rupture Dynamics of Surface and Subsurface Faulting

HR: 1340h
AN: S43A-1050 [Abstracts]
TI: Investigation of Shallow Crustal Weak Zone Effects on Rupture Dynamics of Surface and Subsurface Faulting
AU: * Pitarka, A
EM: arben_pitarka@urscorp.com
AF: URS Corporation, 566 El Dorado St, 2nd floor, Pasadena, CA 91101 United States
AU: Day, S
EM: day@moho.sdsu.edu
AF: San Diego State University, Dept. of Geological Sciences, San Diego, CA 92182 United States
AU: Dalguer, L A
EM: ldalguer@sdsu.edu
AF: San Diego State University, Dept. of Geological Sciences, San Diego, CA 92182 United States
AB: At short and intermediate periods (0.3-3.0 s) the recorded ground motions from earthquakes that produce large surface rupture are systematically weaker than the ground motions from earthquakes whose rupture is confined to the subsurface. Although limited to long periods, the kinematic rupture models give a clear indication that the cause of the observed differences in ground motion level and frequency content produced by surface and subsurface rupture is mainly due to differences in fault rupture dynamics in the shallow (upper 5 km) and middle regions of the crust. These differences in rupture process are linked with contrasts in dynamic stress drop, rupture velocity and slip velocity between these two depth ranges. Among several aspects of rupture dynamics that are depth dependent and have a significant effect on the fracture energy and radiated seismic energy is the velocity strengthening and relatively low dynamic friction in the weak zone (top 5 km of the crust). The effect of the velocity strengthening is significant for shallow slip on existing faults and in soft sedimentary layers. Using rupture dynamic models of M6.5 strike slip scenario earthquakes on faults that break and do not break the surface we investigate the effect of the velocity strengthening in the weak zone on near fault ground motion from surface and subsurface rupture in the frequency range of 0.1-2Hz. We will show results of our 3D finite-difference simulations and discuss their potential use for deriving constraints on maximum values and depth variation of kinematic parameters such as slip velocity and rise time in the weak zone.
DE: 7209 Earthquake dynamics (1242)
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7290 Computational seismology
SC: Seismology [S]
MN: Fall Meeting 2005