Investigation on the Association of Fluid Flux with Temporal Change in Attenuation within Ruptured Fault Zone after Earthquake

Abstract:

Attenuation, noted as 1/ Qs, had been considered as a geophysical parameter related to the fluid content, temperature and fracture of the medium. The fracture zone associated with fault zone could be considered as a fluid reservoir, which possibly yield to some observations/detections of phenomena associated with pre-, co- or post-seismic of a larger earthquake. Several observations had been made recently to investigate the temporal variation of the attenuation within the hanging wall before, following and after the earthquake, e.g. 1999 Chi-Chi earthquake, and 2004 Parkfield earthquake. The study associated with the 1999 Chi-Chi earthquake observed a temporal changes with a diffusion process in Qs by the deduction of about 90 within the fault rupture zone two years following the 1999 Chi-Chi earthquake. The reduction in Qs two years following the Chi-Chi earthquake might indicate high pore-fluid saturation within fractured fault zone rocks due to post-seismic redistribution of the fluid. In this study, we will try to further quantify the observation by considering the conservation theory of the fluid flux within the reservoir and the passage of fluid flux through the fault zones after a large earthquake to examine the possible association of the fluid to the reduction of Qs. This theoretical attempt would provide also the possible basis in understanding the fluid behavior in the fault zone associated with earthquakes.