Does hydrologic circulation mask frictional heat on faults after large earthquakes?

Abstract

[1] Knowledge of frictional resistance along faults is important for understanding the mechanics of earthquakes and faulting. The clearest in situ measure of fault friction potentially comes from temperature measurements in boreholes crossing fault zones within a few years of rupture. However, large temperature signals from frictional heating on faults have not been observed. Unambiguously interpreting the coseismic frictional resistance from small thermal perturbations observed in borehole temperature profiles requires assessing the impact of other potentially confounding thermal processes. We address several issues associated with quantifying the temperature signal of frictional heating including transient fluid flow associated with the earthquake, thermal disturbance caused by borehole drilling, and heterogeneous thermal physical rock properties. Transient fluid flow is investigated using a two-dimensional coupled fluid flow and heat transport model to evaluate the temperature field following an earthquake. Simulations for a range of realistic permeability, frictional heating, and pore pressure scenarios show that high permeabilities (>10 −14 m 2 ) are necessary for significant advection within the several years after an earthquake and suggest that transient fluid flow is unlikely to mask frictional heat anomalies. We illustrate how disturbances from circulating fluids during drilling diffuse quickly leaving a robust signature of frictional heating. Finally, we discuss the utility of repeated borehole temperature profiles for discriminating between different interpretations of thermal perturbations. Our results suggest that temperature anomalies from even low friction should be detectable at depths >1 km 1 to 2 years after a large earthquake and that interpretations of low friction from existing data are likely robust.Citation: Fulton, P. M., R. N. Harris, D. M. Saffer, and E. E. Brodsky (2010), Does hydrologic circulation mask frictional heat on faults after large earthquakes?,

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“…Measurements of the decaying temperature of the fault zone, as well as analyses of the changing stress and chemical properties of the fault rocks, are important observations that need to be made soon after the earthquake (Brodsky et al, 2009;Fulton et al, 2010). The scheduling of this expedition within 13 months following the earthquake reflects the rapid response taken by IODP to provide scientific information about large-scale geohazards that severely impact our societies.…”

“…Data from the measurement of the time decaying temperature anomaly associated with the earthquake slip will be used to estimate the frictional heat produced at the time of the earthquake, which can be used to infer the level of dynamic friction (e.g., Brodsky et al, 2009;Fulton et al, 2010). Measurements of current stress (i.e., postearthquake slip) also can be used to explore different models to explain how dynamic slip occurred and the degree to which stress was released.…”

Recent scientific and operational achievements of D/V Chikyu

“…The main purpose of this fast response was to measure the temperature anomaly thought to remain after any event of high-speed seismic slip, presumably caused by frictional heating. Simulation models indicated that this thermal anomaly would remain detectable if measurements were conducted within two years of the initial earthquake [12].…”

Eos, Transactions, American Geophysical Union Volume 91, Number 27, 6 July 2010

“…Fulton et al [2010] illustrated that temperatures across a fault zone should not be markedly affected by fluid flow driven away from the fault by locally elevated pore pressure (e.g., due to thermal pressurization or shear compaction). Repeated measurements are also important to monitor the evolution of thermal anomalies with time and to separate drilling-induced anomalies from frictional heating signals.…”