Causes of distal volcano-tectonic seismicity inferred from hydrothermal modeling

• Published in: Journal of volcanology and geothermal research Vol. 345; pp. 98 - 108
• Main Authors: Coulon, C.A., Hsieh, P.A., White, R., Lowenstern, J.B., Ingebritsen, S.E.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-10-2017
• ISSN: 0377-0273; 1872-6097
• DOI: 10.1016/j.jvolgeores.2017.07.011

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 (0.04km3) intrusion and explored the effects of flow geometry (channelized vs. radial flow), magma devolatilization rates (0–15kg/s), and intrusion depths (5 and 7.5km, 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 (6km lateral distance, 6km depth) was favored by channelized fluid flow, high devolatilization rates, and permeabilities similar to those found in geothermal reservoirs (k~10−16 to 10−13m2). For channelized flow, magma-induced thermal pressurization alone can generate cases of ∆P≥0.1 bars for all permeabilities in the range 10−16 to 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.
•Precursory distal volcano-tectonic seismicity may reflect magma-induced fluid-pressure pulses that intersect critically stressed faults.•Fluid-pressure transmission is a potentially viable mechanism over a plausibly wide range of permeability structures.•The proximal pressure changes computed for certain scenarios would be sufficiently large to cause surface deformation.