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doi:10.2204/iodp.proc.333.202.2014

Methods

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., 2010, 2011; Raimbourg et al., 2011).

Two syringe pumps (Teledyne ISCO 1000D) control pore fluid pressure and confining pressure (Fig. F5). A pore pressure of 1000 kPa was maintained under drained conditions. Velocity measurements were conducted under isotropic confining pressure conditions. Confining (effective) pressure was increased stepwise in the measurements, pressurized in 10 s and held for 24 h for the next step. The pressure interval ranges from 700 to 9460 kPa, which is at least 2.5 times in situ effective pressure at the sampling depth for each sample (Fig. F6). In situ effective pressure at the sampling depth was calculated from the accumulation of the bulk density of sediments and hydrostatic pore fluid pressures at the depth of recovery (Figs. F3, F4; Table T1). A total of 5–6 steps were tested until in situ effective pressure, and an additional 5–7 steps were measured at least 2.5 times when in situ effective pressure was achieved. Lead zirconate titanate (PZT) shear wave transducers (500 kHz) were employed in a source-receiver pair. PZT in a shear orientation generates a weak compressional mode in addition to its primary shear mode to identify P- and S-wave arrivals in each test. Because S-wave arrival time was often difficult to locate within the coda of the P-wave arrival, S-wave velocity is not shown in this study. Axial displacements were measured during experiments. The change in porosity is obtained from the change in the volume of pore water. The porosity from onboard measurements was used as the porosity at about 100 kPa of effective pressure because the measurements were obtained under atmospheric pressure and wet conditions. In the case that the experimental condition around 100 kPa was not available, the pore volume at 100 kPa was calculated by linear extrapolation from the closest two points of experimental data. The onboard porosity was taken from averaged values of the porosity measured onboard in the 10 m intervals where the sample was obtained at the middle point of the interval (Figs. F3, F4). Error of porosity is defined as the standard deviation of onboard porosity data in the averaged intervals. The error ranges from 0.011 to 0.045 and from 0.013 to 0.028 for analyzed samples from Sites C0011 and C0012, respectively.

Samples were formed into a cylindrical shape, about 3.8 cm in diameter and about 4.5 cm in length. Measurement direction is parallel to the core axis.

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