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Many plate boundary faults, including the San Andreas Fault, appear to slip at unexpectedly low shear stress. One long-standing explanation for a “weak” San Andreas Fault is that fluid release by dehydration reactions during regional metamorphism generates elevated fluid pressures that are localized within the fault, reducing the effective normal stress. We evaluate this hypothesis by calculating realistic fluid production rates for the San Andreas Fault system, and incorporating them into 2-D fluid flow models. Our results show that for a wide range of permeability distributions, fluid sources from crustal dehydration are too small and short-lived to generate, sustain, or localize fluid pressures in the fault sufficient...
Categories: Publication;
Types: Citation;
Tags: San Andreas Fault,
dehydration,
fault strength,
metamorphism,
overpressure,
Geofluids (2010) 10, 193–205AbstractThe variation of permeability with depth can be probed indirectly by various means, including hydrologic models that use geothermal data as constraints and the progress of metamorphic reactions driven by fluid flow. Geothermal and metamorphic data combine to indicate that mean permeability (k) of tectonically active continental crust decreases with depth (z) according to log k ≈ −14–3.2 log z, where k is in m2 and z in km. Other independently derived, crustal-scale k–z relations are generally similar to this power-law curve. Yet there is also substantial evidence for local-to-regional-scale, transient, permeability-generation events that entail permeabilities much higher than...
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