Hydromechanics of a high taper angle, low‐permeability prism: A case study from Peru

Abstract

[1] The Peru frontal prism represents a contrasting hydrologic setting to the better characterized systems of Nankai and Barbados. The high taper angle and convergence rate result in rapid burial of low-permeability sediments. Critical taper stability calculations were combined with a flow model to understand how a steep taper angle could be stable under these conditions. Constant rate flow tests of the slope and prism sediments gave permeability values ranging from a low of $10 À18 m 2 to a high of $10 À16 m 2 . Estimated compaction fluid sources exceed 5 Â 10 À13 s À1 near the toe and remain above 10 À14 s À1 for 20 km arcward in the underthrust sediments. These data were used to constrain a two-dimensional, steady state model of pore pressure along a cross section at 9°S. The model domain is composed of a 15-km-wide frontal prism with a crystalline buttress at the back and 500 m of permeable basement at the base. The combined mechanical stability and flow model analysis yielded a feasible basement permeability of $10 À16 m 2 and a décollement permeability range of 10 À15 -10 À17 m 2 . The model results demonstrate that basement flow and use of different pressure ratio values for the wedge and the base in stability calculations are important for systems with steep taper angles.

Scale dependence of in‐situ permeability measurements in the Nankai accretionary prism: The role of fractures

“…Fluids play an important role in the localization, degree, and nature of faulting at subduction zones, through their impact on effective stress [ Bekins et al , 1995; Davis et al , 1983; Scholz , 1998]. Modeling studies of both accretionary and non‐accretionary subduction zones indicate that fluid permeability is an important control on the development and maintenance of excess pore fluid pressures generated through accretion and compaction processes [ Bekins et al , 1995; Bruckmann et al , 1997; Saffer and Bekins , 1998, 2002; Gamage and Screaton , 2006; Matmon and Bekins , 2006]. Sediment permeability in these settings can vary by several orders of magnitude due to variations in lithology, compaction state, and diagenetic history [e.g., Gamage et al , 2011], changes in effective stress [ Bekins et al , 2011], or the presence of core‐scale fractures [ Brown , 1995].…”

Hydrostratigraphy as a control on subduction zone mechanics through its effects on drainage: an example from the Nankai Margin, SW Japan

“…Numerical models have also emerged as powerful tools to study pore pressure development, and in particular to quantitatively explore the relative roles of sediment permeability, sediment thickness, fault zone permeability, loading rate, clay dehydration, and hydrologic communication between the compacting sediments and underlying basaltic ocean crust (e.g., Screaton et al. 1990; Matmon & Bekins 2006; Screaton 2006). For example, several recent studies have investigated the dewatering of sediments underthrust beneath the décollement using coupled 1D models describing fluid flow and deformation (e.g., Screaton & Saffer 2005; Gamage & Screaton 2006; Screaton 2006; Skarbek & Saffer 2009).…”

Coupled Evolution of Deformation, Pore Fluid Pressure, and Fluid Flow in Shallow Subduction Forearcs

“…Several geological, tectonic, and hydraulic factors vary between subduction margins and are thought to impact fluid and deformation processes (e.g., Clift & Vannucchi, 2004; Ranero et al, 2008; Matmon & Bekins, 2006; Screaton, 2006; Saffer & Bekins, 2002, 2006). For example, sediment permeability strongly controls the dewatering rate.…”