Publication Date:
2008-09-14
Description:
Aqueous fluids are thought to have an essential role in faulting and the dynamic propagation of earthquake rupture. Fluid overpressure can affect earthquake nucleation and in a process termed thermal pressurization, pore fluid pressure produced by frictional heating can reduce the effective normal stress acting on the fault surface. This may lead to a marked reduction in fault strength during slip. However, the coseismic presence of fluids within slip zones and the role of fluids in dynamic fault weakening is still a matter of debate. Here we present compositions of major and trace elements as well as isotope ratios of core samples representing relatively undamaged as well as very fine-grained deformed material from three active zones of the Chelungpu fault, Taiwan. Depth profiles across the most intensely sheared bands that range in thickness from 2-15 cm exhibit sharp compositional peaks of fluid-mobile elements and of strontium isotopes. We suggest that high-temperature fluids (〉350 C) derived from heating of sediment pore fluids during the earthquake interacted with material within the fault zone and mobilized the elements. The coseismic presence of high-temperature fluids under conditions of low hydraulic diffusivity within the fault zone is favourable for thermal pressurization. This effect may have caused a dynamic decrease of friction along the Chelungpu fault during the 1999 magnitude 7.6 Chi-Chi earthquake. © 2008 Macmillan Publishers Limited.
Print ISSN:
1752-0894
Electronic ISSN:
1752-0908
Topics:
Geosciences
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