Extreme hydrothermal conditions at an active plate-bounding fault

Rupert Sutherland, John Townend, Virginia G. Toy, Phaedra Upton, Jamie Coussens, Michael Allen, Laura-May Baratin, Nicolas Barth, Leeza Becroft, Carolin Boese, Austin Boles, Carolyn Boulton, Neil G. R. Broderick, Lucie Janku-Capova, Brett M. Carpenter, Bernard Celerier, Calum Chamberlain, Alan Cooper, Ashley Coutts, Simon C. CoxLisa Craw, Mai-Linh Doan, Jennifer Eccles, Dan Faulkner, Jason Grieve, Julia Grochowski, Anton Gulley, Arthur Hartog, Jamie Howarth, Katrina Jacobs, Tamara Jeppson, Naoki Kato, Steven Keys, Martina Kirilova, Yusuke Kometani, Rob Langridge, Weiren Lin, Timothy Little, Adrienn Lukacs, Deirdre Mallyon, Elisabetta Mariani, Cecile Massiot, Loren Mathewson, Ben Melosh, Catriona Dorothy Menzies, Jo Moore, Luiz Morales, Chance Morgan, Hiroshi Mori, Andre Niemeijer, Osamu Nishikawa, Dave Prior, Katrina Sauer, Martha Savage, Anja M. Schleicher, Doug R. Schmitt, Norio Shigematsu, Sam Taylor-Offord, Damon A. H. Teagle, Harold Tobin, Robert Valdez, Konrad Weaver, Thomas Wiersberg, Jack Williams, Martin Zimmer

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Abstract

Temperature and fluid pressure conditions control rock deformation and mineralization on geological faults, and hence the distribution of earthquakes1. Typical intraplate continental crust has hydrostatic fluid pressure and a near-surface thermal gradient of 31 ± 15 degrees Celsius per kilometre2,3. At temperatures above 300–450 degrees Celsius, usually found at depths greater than 10–15 kilometres, the intra-crystalline plasticity of quartz and feldspar relieves stress by aseismic creep and earthquakes are infrequent. Hydrothermal conditions control the stability of mineral phases and hence frictional–mechanical processes associated with earthquake rupture cycles, but there are few temperature and fluid pressure data from active plate-bounding faults. Here we report results from a borehole drilled into the upper part of the Alpine Fault, which is late in its cycle of stress accumulation and expected to rupture in a magnitude 8 earthquake in the coming decades4,5. The borehole (depth 893 metres) revealed a pore fluid pressure gradient exceeding 9 ± 1 per cent above hydrostatic levels and an average geothermal gradient of 125 ± 55 degrees Celsius per kilometre within the hanging wall of the fault. These extreme hydrothermal conditions result from rapid fault movement, which transports rock and heat from depth, and topographically driven fluid movement that concentrates heat into valleys. Shear heating may occur within the fault but is not required to explain our observations. Our data and models show that highly anomalous fluid pressure and temperature gradients in the upper part of the seismogenic zone can be created by positive feedbacks between processes of fault slip, rock fracturing and alteration, and landscape development at plate-bounding faults.
Original languageEnglish
Pages (from-to)137-140
Number of pages4
JournalNature
Volume546
Early online date17 May 2017
DOIs
Publication statusPublished - 1 Jun 2017

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Sutherland, R., Townend, J., Toy, V. G., Upton, P., Coussens, J., Allen, M., ... Zimmer, M. (2017). Extreme hydrothermal conditions at an active plate-bounding fault. Nature, 546, 137-140. https://doi.org/10.1038/nature22355