Data report: permeability and microfabric of core samples from IODP Expedition 348, Hole C0002P, Nankai Trough accretionary prism

Permeability controls fluid flow in the Earth's crust and affects a wide range of processes including advective transport and pore pressure generation. However, in situ measurements of permeability are few, especially in active tectonic settings or at scales relevant to regional flow. We analyze formation fluid pressure records from oceanic boreholes in the Nankai accretionary prism offshore southwest Japan, focusing on unexpected responses to drilling operations conducted at boreholes ~100 m to the northeast. We develop a 2‐D numerical model of transient fluid flow and conduct a parametric grid search to define hydraulic diffusivity. A value of 0.19–0.46 m2/s (corresponding to a permeability of 9.8 × 10−13 to 2.4 × 10−12 m2) yields the best fit to observed pressure responses. Together with laboratory measurements on core samples and drillstrem tests reported in previous studies, our analysis indicates a strong scale dependence of permeability, likely reflecting the presence of permeable faults and fractures.

Section: Implications For Scale Dependence and Hydrological Processesmentioning

confidence: 99%

Section: Implications For Scale Dependence and Hydrological Processesmentioning

confidence: 99%

In Situ Permeability and Scale Dependence of an Active Accretionary Prism Determined From Cross‐Borehole Experiments

Kinoshita

Saffer

2018

“…The Katz‐Thompson permeability (Katz & Thompson, 1986, 1987) of the sample from Hole C0002R is ∼3 × 10 −19 m 2 , which is 2 orders of magnitude lower than reported by Song and Underwood (2017) at ∼2,200 mbsf based on constant‐flow permeability tests.…”

Section: Resultsmentioning

confidence: 53%

Effective Porosity Profile at IODP Site C0002 in the Heart of the Nankai Accretionary Prism, and Its Use for Predicting In Situ Seismic Velocities

Doan

Dutilleul

Henry

2023

Using logging data and samples collected by the four expeditions of the International Ocean Discovery Program NanTroSEIZE drilling campaign that occupied Site C0002 in the Nankai margin located southwest of Japan, we determined effective porosity and sonic velocity profiles down to 3 km below the seafloor in the accretionary prism, above the seismogenic plate interface. We measured cation exchange capacity to differentiate clay‐bound water content from effective porosity, which is representative of compaction. The decrease in effective porosity with depth is fitted with a single exponential decay, which suggests hydrostatic conditions for most of the borehole. The Erickson‐Jarrard template was adapted to account for the actual clay‐bearing nature of the sediments. We used this improved P‐wave velocity–effective porosity relationship to fill shipboard data gaps and predict P‐ and S‐wave velocity profiles at Site C0002.

Transient Permeability of a Deep‐Seated Subduction Interface Shear Zone

Muñoz‐Montecinos,

Behr

2023

Slow slip and tremor is observed along many subduction margins and is commonly linked to fluid pressure variations and migration. Accurate estimates of porosity and permeability around subduction megathrust shear zones are vital for understanding fluid‐seismicity interactions. We use high‐resolution digital outcrop data and (micro)structural analysis to assess transient permeability and porosity of a deep‐seated subduction interface exposed on Syros Island, Greece. We document the orientations, relative timing, and opening aperture (based on crack‐seal textures) of veins that were emplaced synkinematically with ductile deformation during early exhumation within the subduction channel. Our findings indicate high permeability through vein‐filled fractures amidst a lower permeability matrix, with transient, fracture‐controlled permeabilities ranging from 10−14 to 10−15 m2 and fracture porosities of 1%–10%. These estimates align with low‐end values from seismological/geodetic observations in active subduction zones, and are also consistent with fault‐valve‐like numerical models that suggest high background‐to‐transient permeability contrasts favor unstable slip.