Acoustic and mechanical properties of Nankai accretionary prism core samples

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doi: 10.1029/2010GC003169
Author(s): Raimbourg, Hugues; Hamano, Yozo; Saito, Saneatsu; Kinoshita, Masataka; Kopf, Achim J.
Author Affiliation(s): Primary:
JAMSTEC, Yokosuka, Japan
Other:
University of Bremen, Germany
Volume Title: Geochemistry, Geophysics, Geosystems - G<sup>3</sup>
Source: Geochemistry, Geophysics, Geosystems - G>3`, Vol.12. Publisher: American Geophysical Union and The Geochemical Society, United States. ISSN: 1525-2027
Note: In English. 83 refs.; illus., incl. 1 table, sketch map
Summary: We studied undeformed sediment and accreted strata recently recovered by Ocean Drilling Program/Integrated Ocean Drilling Program (ODP/IODP) drilling in Nankai Trough convergent margin to unravel the changes in physical properties from initial deposition to incipient deformation. We have derived acoustic (Vp) and mechanical (uniaxial poroelastic compliance, compaction amplitude) properties of samples from various drill sites along the Muroto (ODP 1173) and Kii transects (IODP C0001, C0002, C0006, and C0007) from isotropic loading tests where confining and pore pressure were independently applied. We quantified the dependence of Vp on both effective (Peff) and confining (Pc) pressure, which can be used to correct atmospheric pressure measurements of Vp. Experimental Vp obtained on core samples extrapolated to in situ conditions are slightly higher than logging-derived velocities, which can be attributed either to velocity dispersion or to the effect of large-scale faults and weak zones on waves with longer wavelength. In the high-porosity (30%-60%) tested sediments, velocities are controlled at first order by porosity and not by lithology, which is in agreement with our static measurements of drained framework incompressibility, much smaller than fluid incompressibility. Rather than framework incompressibility, shear modulus is probably the second-order control on Vp, accounting for most of the difference between actual Vp and the prediction by Wood's (1941) suspension model. We also quantified the mechanical state of Nankai samples in terms of anisotropy, diagenesis, and consolidation. Both acoustic and mechanical parameters reveal similar values in vertical and horizontal directions, attesting to the very low anisotropy of the tested material. When considering the porous samples of the Upper Shikoku Basin sediments (Site 1173) as examples of diagenetically cemented material, several mechanical and acoustic attributes appeared as reliable experimental indicators of the presence of intergrain cementation. We also detected incipient cementation in samples from IODP Site C0001 (accretionary prism unit). In terms of consolidation, we distinguished two classes of material response (shallow, deformable samples and deep, hardly deformable ones) based on the amount of compaction upon application of a Peff large with respect to the inferred in situ value, with a transition that might be related to a critical porosity.
Year of Publication: 2011
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Acoustical methods; Acoustical properties; Asia; Body waves; Compaction; Elastic waves; Expedition 316; Experimental studies; Far East; Geophysical methods; Honshu; IODP Site C0001; IODP Site C0002; IODP Site C0006; IODP Site C0007; Integrated Ocean Drilling Program; Japan; Kii Peninsula; Kochi Japan; Marine geology; Mechanical properties; Muroto Japan; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; ODP Site 1173; Ocean Drilling Program; P-waves; Pacific Ocean; Seismic waves; Shikoku; Shikoku Basin; Velocity; West Pacific
Coordinates: N310000 N350000 E1390000 E1320000
Record ID: 2013046508
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