Pressure and stress prediction in the Nankai accretionary prism; a critical state soil mechanics porosity-based approach

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doi: 10.1002/2017JB015025
Author(s): Flemings, Peter B.; Saffer, Demian M.
Author Affiliation(s): Primary:
University of Texas at Austin, Department of Geological Sciences, Austin, TX, United States
Pennsylvania State University, United States
Volume Title: Journal of Geophysical Research: Solid Earth
Source: Journal of Geophysical Research: Solid Earth, 123(2), p.1089-1115. Publisher: Wiley-Blackwell for American Geophysical Union, Washington, DC, United States. ISSN: 2169-9313
Note: In English. 95 refs.; illus., incl. sect., strat. col., 3 tables, sketch map
Summary: We predict pressure and stress from porosity in the Nankai accretionary prism with a critical state soil model that describes porosity as a function of mean stress and maximum shear stress, and assumes Coulomb failure within the wedge and uniaxial burial beneath it. At Ocean Drilling Program Sites 1174 and 808, we find that pore pressure in the prism supports 70% to 90% of the overburden (λu = 0.7 to 0.9), for a range of assumed friction angles (5-30°). The prism pore pressure is equal to or greater than that in the underthrust sediments even though the porosity is lower within the prism. The high pore pressures lead to a mechanically weak wedge that supports low maximum shear stress, and this in turn requires very low basal traction to remain consistent with the observed narrowly tapered wedge geometry. We estimate the decollement friction coefficient (µb) to be ∼0.08-0.38 (Φb' = 4.6°-21°). Our approach defines a pathway to predict pressure in a wide range of environments from readily observed quantities (e.g., porosity and seismic velocity). Pressure and stress control the form of the Earth's collisional continental margins and play a key role in its greatest earthquakes. However, heretofore, there has been no systematic approach to relate material state (e.g., porosity), pore pressure, and stress in these systems. Abstract Copyright (2018), . American Geophysical Union. All Rights Reserved.
Year of Publication: 2018
Research Program: ODP Ocean Drilling Program
Key Words: 30 Engineering Geology; Accretionary wedges; Compression; Continental margin; Cores; Decollement; Equations; Eurasian Plate; Failures; Friction; Geometry; Geophysical methods; Geophysical profiles; Geophysical surveys; Leg 190; Lithostratigraphy; Models; Nankai Trough; North Pacific; Northwest Pacific; ODP Site 1174; ODP Site 808; Ocean Drilling Program; Overburden; Pacific Ocean; Pacific Plate; Philippine Sea Plate; Plate collision; Plate tectonics; Pore pressure; Porosity; Pressure; Processes; Quantitative analysis; Sampling; Seismic methods; Seismic profiles; Shear stress; Shikoku Basin; Soil mechanics; Strength; Stress; Surveys; West Pacific
Coordinates: N322000 N322100 E1345800 E1345700
N321500 N321500 E1350200 E1350200
N322105 N322111 E1345646 E1345634
Record ID: 2018083203
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom