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

2017; Wiley; Volume: 18; Issue: 12 Linguagem: Inglês

10.1002/2017gc007202

1525-2027

John Townend, R. Sutherland, Virginia Toy, Mai‐Linh Doan, Bernard Célérier, Cécile Massiot, Jamie Coussens, T.N. Jeppson, Lucie Janků-Čápová, Léa Remaud, Phædra Upton, Douglas R. Schmitt, Philippe Pézard, Jack Williams, Michael J. Allen, Laura‐May Baratin, Nicolas C. Barth, Leeza Becroft, Carolin Boese, Carolyn Boulton, Neil G. R. Broderick, B. M. Carpenter, C. J. Chamberlain, Alan F. Cooper, Ashley Coutts, Simon C. Cox, Lisa Craw, J. D. Eccles, D. R. Faulkner, Jason Grieve, Julia Grochowski, Anton Gulley, A.H. Hartog, Gilles Henry, Jamie Howarth, Katrina Jacobs, Naoki Kato, Steven Keys, Martina Kirilova, Yusuke Kometani, R. M. Langridge, Weiren Lin, Tim Little, Adrienn Lukács, Deirdre Mallyon, Elisabetta Mariani, Loren Mathewson, Ben Melosh, C.D. Menzies, Jo Moore, Luis Morales, Hiroshi Mori, André Niemeijer, Osamu Nishikawa, O. Nitsch, J. Paris, David J. Prior, Katrina Sauer, M. K. Savage, Anja M. Schleicher, Norio Shigematsu, Sam Taylor‐Offord, D.A.H. Teagle, Harold Tobin, Robert Valdez, Konrad Weaver, Thomas Wiersberg, Martin Zimmer,

Geological and Geochemical Analysis

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 m 2 ) 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.