Collaborative Research (USC/UCLA/UCR/SDSU): Continuing Study of Internal Structure, Dynamic Rupture, and Post-Earthquake Healing of the Hector Mine Rupture Zone

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Proposal Title: Collaborative Research (USC/UCLA/UCR): Continuing Study of Internal Structure, Rupture, and Post-Earthquake Healing of the Hector Mine Rupture Zone.NSF Proposal Number: EAR-0229324, 0229452, 0229678Principal Investigators: Yong-Gang Li, John E. Vidale, and David D. OglesbyABSTRACT We propose to continue our study of post-earthquake healing, fault zone process, and dynamic rupture of the 1999 M7.1 Hector Mine, California, earthquake using fault-zone trapped waves. Observations and FD simulations of fault-zone trapped waves generated by aftershocks and explosions, and recorded at linear seismic arrays deployed across the Hector Mine surface rupture, have revealed a ~100 m wide low-velocity waveguide along the rupture zone, and the bifurcation of northern rupture at the seismogenic depth. Our previous work has also shown that this low-velocity waveguide has healed since the mainshock, with P and S wave velocities increasing by ~1% between 2000 and 2001. Continued monitoring of healing in the Hector Mine rupture zone will help us to see if its healing rate slows with time, as did the healing rate at Landers. In the present proposal, we shall 1) repeat the experiment in 2003 to find further evidence of the time- and spatial-dependence of fault healing; 2) develop a mechanical model based on crack dilatancy theory combined with chemical sealing for interpretation of fault healing; 3) simulate dynamic rupture on multiple fault segments and relate these models to the extent of damage to the rock mass in fault zone; 4) analyze shear-wave splitting for study of the near-fault stress state and its temporal variation; 5) compare the fault healing at Hector Mine with that at Landers for understanding the fault interaction in a parallel-fault system. Through this project, we will obtain a better understanding for the relationships between the fault zone internal structure, rupture process, and earthquake cycle. Knowledge of spatial and temporal variations in the fault structure will help resolve more realistic macroscopic representations of fault-strength variations and the dynamic response of fault segments and fault networks as well as predict behavior of future earthquake.