Petrophysical, Geochemical, and Hydrological Evidence for Extensive Fracture-Mediated Fluid and Heat Transport in the Alpine Fault's Hanging-Wall Damage Zone

John Townend (Corresponding Author), Rupert Sutherland, Virginia G. Toy, Mai-Linh Doan, Bernard Celerier, Cecile Massiot, Jamie Coussens, Tamara Jeppson, Lucie Janku-Capova, Lea Remaud, Phaedra Upton, Doug R. Schmitt, Philippe Pezard, Jack Williams, Michael Allen, Laura-May Baratin, Nicolas Barth, Catriona Dorothy Menzies

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Abstract

Fault rock assemblages reflect interaction between deformation, stress, temperature, fluid, and chemical regimes on distinct spatial and temporal scales at various positions in the crust. Here we interpret measurements made in the hanging‐wall of the Alpine Fault during the second stage of the Deep Fault Drilling Project (DFDP‐2). We present observational evidence for extensive fracturing and high hanging‐wall hydraulic conductivity (∼10−9 to 10−7 m/s, corresponding to permeability of ∼10−16 to 10−14 m2) extending several hundred meters from the fault's principal slip zone. Mud losses, gas chemistry anomalies, and petrophysical data indicate that a subset of fractures intersected by the borehole are capable of transmitting fluid volumes of several cubic meters on time scales of hours. DFDP‐2 observations and other data suggest that this hydrogeologically active portion of the fault zone in the hanging‐wall is several kilometers wide in the uppermost crust. This finding is consistent with numerical models of earthquake rupture and off‐fault damage. We conclude that the mechanically and hydrogeologically active part of the Alpine Fault is a more dynamic and extensive feature than commonly described in models based on exhumed faults. We propose that the hydrogeologically active damage zone of the Alpine Fault and other large active faults in areas of high topographic relief can be subdivided into an inner zone in which damage is controlled principally by earthquake rupture processes and an outer zone in which damage reflects coseismic shaking, strain accumulation and release on interseismic timescales, and inherited fracturing related to exhumation.
Original languageEnglish
Pages (from-to)4709-4732
Number of pages24
JournalGeochemistry, Geophysics, Geosystems
Volume18
Issue number12
Early online date7 Dec 2017
DOIs
Publication statusPublished - Dec 2017

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Keywords

  • seismogenesis
  • topography
  • damage zone
  • hydrogeology
  • fault zone
  • petrophysics

Cite this

Townend, J., Sutherland, R., Toy, V. G., Doan, M-L., Celerier, B., Massiot, C., Coussens, J., Jeppson, T., Janku-Capova, L., Remaud, L., Upton, P., Schmitt, D. R., Pezard, P., Williams, J., Allen, M., Baratin, L-M., Barth, N., & Menzies, C. D. (2017). Petrophysical, Geochemical, and Hydrological Evidence for Extensive Fracture-Mediated Fluid and Heat Transport in the Alpine Fault's Hanging-Wall Damage Zone. Geochemistry, Geophysics, Geosystems , 18(12), 4709-4732. https://doi.org/10.1002/2017GC007202