Causes of distal volcano-tectonic seismicity inferred from hydrothermal modeling

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Abstract

Distal volcano-tectonic (dVT) seismicity typically precedes eruption at long-dormant volcanoes by days to years. Precursory dVT seismicity may reflect magma-induced fluid-pressure pulses that intersect critically stressed faults. We explored this hypothesis using an open-source magmatic-hydrothermal code that simulates multiphase fluid and heat transport over the temperature range 0 to 1200 °C. We calculated fluid-pressure changes caused by a small (0.04 km3) intrusion and explored the effects of flow geometry (channelized vs. radial flow), magma devolatilization rates (0–15 kg/s), and intrusion depths (5 and 7.5 km, above and below the brittle-ductile transition). Magma and host-rock permeabilities were key controlling parameters and we tested a wide range of permeability (k) and permeability anisotropies (kh/kv), including k constant, k(z), k(T), and k(z, T, P) distributions, examining a total of ~ 1600 realizations to explore the relevant parameter space. Propagation of potentially causal pressure changes (ΔP ≥ 0.1 bars) to the mean dVT location (6 km lateral distance, 6 km depth) was favored by channelized fluid flow, high devolatilization rates, and permeabilities similar to those found in geothermal reservoirs (k ~ 10− 16to 10− 13m2). For channelized flow, magma-induced thermal pressurization alone can generate cases of ∆ P ≥ 0.1 bars for all permeabilities in the range 10− 16to 10− 13m2, whereas in radial flow regimes thermal pressurization causes ∆ P < 0.1 bars for all permeabilities. Changes in distal fluid pressure occurred before proximal pressure changes given modest anisotropies (kh/kv~ 10–100). Invoking k(z,T,P) and high, sustained devolatilization rates caused large dynamic fluctuations in k and P in the near-magma environment but had little effect on pressure changes at the distal dVT location. Intrusion below the brittle-ductile transition damps but does not prevent pressure transmission to the dVT site.

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APA

Coulon, C. A., Hsieh, P. A., White, R., Lowenstern, J. B., & Ingebritsen, S. E. (2017). Causes of distal volcano-tectonic seismicity inferred from hydrothermal modeling. Journal of Volcanology and Geothermal Research, 345, 98–108. https://doi.org/10.1016/j.jvolgeores.2017.07.011

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