Elevated fluid pressure and extreme mechanical weakness of a plate boundary thrust, Nankai Trough subduction zone

Research Article| August 01, 2009 Elevated fluid pressure and extreme mechanical weakness of a plate boundary thrust, Nankai Trough subduction zone Harold J. Tobin; Harold J. Tobin * 1Department of Geology and Geophysics, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA *E-mail: htobin@wisc.edu. Search for other works by this author on: GSW Google Scholar Demian M. Saffer Demian M. Saffer 2Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Harold J. Tobin * 1Department of Geology and Geophysics, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA Demian M. Saffer 2Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802, USA *E-mail: htobin@wisc.edu. Publisher: Geological Society of America Received: 18 Dec 2008 Revision Received: 16 Mar 2009 Accepted: 17 Mar 2009 First Online: 03 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2009 Geological Society of America Geology (2009) 37 (8): 679–682. https://doi.org/10.1130/G25752A.1 Article history Received: 18 Dec 2008 Revision Received: 16 Mar 2009 Accepted: 17 Mar 2009 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation Harold J. Tobin, Demian M. Saffer; Elevated fluid pressure and extreme mechanical weakness of a plate boundary thrust, Nankai Trough subduction zone. Geology 2009;; 37 (8): 679–682. doi: https://doi.org/10.1130/G25752A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Pore fluid pressure is a key parameter governing both the shear strength of faults and the conditions for seismic and tsunamigenic slip on subduction zone megathrusts. However, quantitative constraints on this parameter based on in situ data in these, or any, faults have proven elusive. Using seismic interval velocities derived from a three-dimensional seismic reflection survey, we compute porosity, fluid pressure, and effective stress at the plate interface in the Nankai Trough subduction zone (offshore southwestern Japan) to 20 km down the fault dip using well-constrained, locally calibrated empirical relationships between velocity, porosity, and effective stress. We show that the fault and immediately subjacent footwall are nearly undrained, implying that the subduction megathrust slips under a shear stress of <~4 MPa throughout the study area and that fault shear strength remains nearly constant despite increasing depth. Computed pore pressures are in excellent agreement with independent hydrological model results, and are perhaps the best constrained and most spatially extensive estimates of pore pressure within a plate boundary fault system and subducted sediments. This elevated pore pressure offers a plausible and quantifiable explanation for the mechanical weakness of the fault and the suppression of stick-slip seismogenic behavior in the updip region. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.