Raimbourg, Hugues et al. (2011): Acoustic and mechanical properties of Nankai accretionary prism core samples

IODP 316
IODP 314 C0001
IODP 315 C0001
IODP 314 C0002
IODP 315 C0002
IODP 326 C0002
IODP 332 C0002
IODP 338 C0002
IODP 314 C0006
IODP 316 C0006
IODP 316 C0007


Raimbourg, Hugues
JAMSTEC, Yokosuka, Japan

Hamano, Yozo
University of Bremen, Germany

Saito, Saneatsu

Kinoshita, Masataka

Kopf, Achim J.

Acoustic and mechanical properties of Nankai accretionary prism core samples
Geochemistry, Geophysics, Geosystems - G (super 3)
American Geophysical Union and The Geochemical Society, United States
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 (V (sub p) ) 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 V (sub p) on both effective (P (sub eff) ) and confining (P (sub c) ) pressure, which can be used to correct atmospheric pressure measurements of V (sub p) . Experimental V (sub p) 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 V (sub p) , accounting for most of the difference between actual V (sub p) 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 P (sub eff) large with respect to the inferred in situ value, with a transition that might be related to a critical porosity.
Coverage:Geographic coordinates:
West:132.0000East: 139.0000

Oceanography; acoustical methods; acoustical properties; Asia; body waves; compaction; elastic waves; Expedition 316; experimental studies; Far East; geophysical methods; Honshu; Integrated Ocean Drilling Program; IODP Site C0001; IODP Site C0002; IODP Site C0006; IODP Site C0007; Japan; Kii Peninsula; Kochi Japan; marine geology; mechanical properties; Muroto Japan; Nankai Trough; NanTroSEIZE; North Pacific; Northwest Pacific; Ocean Drilling Program; ODP Site 1173; P-waves; Pacific Ocean; seismic waves; Shikoku; Shikoku Basin; velocity; West Pacific;