Inferred pore pressures at the Costa Rica subduction zone; implications for dewatering processes

Author(s): Saffer, Demian M.; Silver, Eli A.; Fisher, Andrew T.; Tobin, Harold; Moran, Kate
Author Affiliation(s): Primary:
University of California, Institute of Tectonics, Santa Cruz, CA, United States
New Mexico Institute of Mining and Technology, Socorro, NM, United States
Bedford Institute of Oceanography, Dartmouth, NS, Canada
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 177(3-4), p.193-207. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 28 refs.; illus., incl. sect., sketch map
Summary: Drilling on Ocean Drilling Program (ODP) Leg 170, offshore Costa Rica indicates that the entire incoming sedimentary section is underthrust. Thus, observed changes in the thickness of underthrust sediments as they are progressively buried beneath the margin wedge provide a direct measure of the rate and magnitude of sediment dewatering. Laboratory consolidation tests indicate that in situ excess pore-fluid pressures within the underthrust section range from 1.3 MPa at the top of the section to 3.1 MPa near the base. The inferred pore pressure profile implies that fluids escape the uppermost sediments most rapidly, whereas the basal sediments remain essentially undrained. This interpretation suggests that the sedimentary and underlying ocean crustal hydrologic systems are decoupled. We use a simple model of fluid flow to demonstrate that dewatering of the underthrust sediments can occur via lateral flow only if sediment permeability is strongly anisotropic, or if flow is focused along permeable stratigraphic layers. If significant dewatering occurs by vertical fluid flow, it must occur within closely spaced, high-permeability conduits. Abstract Copyright (2000) Elsevier, B.V.
Year of Publication: 2000
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 18 Geophysics, Solid-Earth; Central America; Consolidation; Consolidometer tests; Continental margin; Costa Rica; Dehydration; Density; East Pacific; Experimental studies; Faults; Fluid pressure; Geophysical profiles; Geophysical surveys; Laboratory studies; Leg 170; Marine sediments; Nicoya Peninsula; Numerical models; ODP Site 1039; ODP Site 1040; ODP Site 1043; Ocean Drilling Program; One-dimensional models; Pacific Ocean; Permeability; Plate convergence; Plate tectonics; Pore pressure; Sediments; Seismic profiles; Subduction zones; Surveys; Underthrust faults
Coordinates: N093000 N100000 W0853500 W0863000
Record ID: 2000039347
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands