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doi:10.2204/iodp.proc.314315316.219.2012

Results

Frictional healing

Frictional healing exhibits a linear relationship with the logarithm of hold time for holds longer than 10 s for samples from both Sites C0004 and C0007 (Figs. F8, F9). For 1000 s holds, Δµ ranges from 0.009 to 0.023 for samples from Site C0004 and from 0.008 to 0.020 for samples from Site C0007 (Tables T2, T3). Healing rates range from ~0.005 to 0.008 per decade for samples from Site C0004 and are slightly lower for samples from Site C0007, ranging from ~0.003 to 0.007 per decade (Table T4). The healing rate exhibits a weakly increasing trend with depth at Site C0004 and a decreasing trend with depth at Site C0007 (Figs. F8, F9). There is little difference between sample healing rates from within fault zones compared to samples from wall rock.

Compaction

Compaction rate also generally exhibits a linear relation with the logarithm of hold time for holds longer than ~10 s (Figs. F10, F11). However, some samples exhibited slight nonlinearity, showing concave upward trends (Fig. F10). For 1000 s holds, normal strain (ε) from compaction ranges from 0.005 to 0.016 at both Sites C0004 and C0007 (Tables T2, T3). Compaction rates for the two sites are also similar, ranging from ~0.002 to 0.007 per decade. Compaction data as a function of logarithmic hold time in the 10–1000 s range are well fit linearly, with R2 > 0.95 for both sites, including those that show some nonlinearity (Table T4). Compaction rates decrease with increasing distance from the fault zone at Site C0004 and appear to increase with depth at Site C0007.

Compressibility

Compressibility was calculated from linear fits to layer-normal strains in response to changes in effective normal stress; we conducted these experiments only for specimens from Site C0004 (Fig. F12; Table T5). Compressibility values range from 0.89 to 3.85 GPa–1, and the corresponding Young’s modulus ranges from 0.26 to 1.12 GPa (Table T6). Compressibility is highest within the fault zone but otherwise does not exhibit any clear trend downsection (Fig. F12).