Tectonic signatures in centimeter‐scale velocity‐porosity relationships of Costa Rica convergent margin sediments

Abstract

[1] The Costa Rica convergent margin, investigated during Ocean Drilling Program Leg 170, offers a unique opportunity to compare the tectonic effects of rapid subduction on incoming oceanic sediments to their laterally equivalent underthrust counterparts and to terrestrially derived wedge materials. Elevated pressure laboratory measurements of ultrasonic compressional and shear wave velocity, and porosity, are used to examine the importance of tectonic, lithologic, and diagenetic controls on physical and elastic properties of sediments in these three key tectonic domains. Depositional and stress path histories of the three domains, for example, can be distinguished by (1) trends of in situ velocity-porosity (and derived measurements) correspondence and (2) the mechanical response of representative materials to isotropic consolidation. A compressional wave velocity-porosity model, critical for the application of seismic imaging to margin-wide physical property and mass balance estimates, is developed from the laboratory measurements and shown to be consistent with the information derived from LWD bulk density and migrated seismic reflection data. This consistency of the velocityporosity model over the large range of both frequency and length measurement scales is a key result, supporting the assertion that core and borehole physical property measurements can be extrapolated to larger domains. Finally, dewatering and overpressure effects, critical factors in subduction zone and fault process dynamics and increasingly common multiphase/converted wave imaging targets, are discussed in terms of laboratoryestimated in situ compressional and shear wave velocity relationships. INDEX TERMS:5114 Physical Properties of Rocks: Permeability and porosity; 8105 Tectonophysics: Continental margins and sedimentary basins (1212); 3022 Marine Geology and Geophysics: Marine sediments-processes and transport; KEYWORDS: subduction zones, elastic properties, dewatering Citation: Gettemy, G. L., and H. J. Tobin, Tectonic signatures in centimeter-scale velocity-porosity relationships of Costa Rica convergent margin sediments,

Velocity‐porosity relationships for slope apron and accreted sediments in the Nankai Trough Seismogenic Zone Experiment, Integrated Ocean Drilling Program Expedition 315 Site C0001

“…Many studies have examined these properties in various sediments. The relationships between compressional wave velocity and porosity have also been reported [e.g., Raymer et al, 1980;Marion et al, 1992;Hyndman et al, 1993;Erickson and Jarrard, 1998;Gettemy and Tobin, 2003;Hoffman and Tobin, 2004;Spinelli et al, 2007]. Comparison of relationships between compressional velocity and porosity for various depositional histories presented in this study will identify characteristics of accreted sediments expressed by quantitative physical properties.…”

“…The design of the experiment is similar to that employed in other studies of saturated marine sediments [e.g., Tobin et al, 1994;Tobin and Moore, 1997;Gettemy and Tobin, 2003]. …”

“…As sediments are buried and tectonically incorporated into the prism, porosity decreases, causing an increase in the effective elastic moduli of the sediments. The physical properties of these sediments evolve in various ways in response to changes in the large-scale architecture, deformation, mass balance, and seismogenic behavior of subduction zones [e.g., Bangs and Westbook, 1991;von Huene and Scholl, 1991;Moore and Vrolijk, 1992;Erickson and Jarrard, 1998;Bilek and Lay, 1999;Moore and Saffer, 2001;Gettemy and Tobin, 2003;Saffer, 2007].…”

Data report: compressional wave velocity measurements on sediments from the reference site off Kumano, Nankai Trough, NantroSEIZE Expedition 333

“…The design of the experiment is similar to that employed in other studies of saturated marine sediments (e.g., Tobin et al, 1994;Tobin and Moore, 1997;Gettemy and Tobin, 2003;Hashimoto et al, 2010Hashimoto et al, , 2011Raimbourg et al, 2011).…”

“…The change in physical properties from incoming sediment to accretionary prisms is a key to understanding mass balance of sediments, fluid flux, heat transportation, wedge architecture, and seismic behavior at a subduction interface (e.g., Bangs and Westbrook, 1991;von Huene and Scholl, 1991;Moore and Vrolijk, 1992;Erickson and Jarrard, 1998;Bilek and Lay, 1999;Moore and Saffer, 2001;Gettemy and Tobin, 2003;Saffer, 2007). Although Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Experiment (NanTroSEIZE) Stage 1 was conducted targeting sediments in the wedge, slope basins, backarc basin, decollement, and shallow portion of the megasplay fault, incoming sediments at the reference sites located oceanward of the deformation front were drilled during IODP NanTroSEIZE Stage 2 Expeditions 322 and 333.…”