Figure 3

Seismic section, inverted resistivity model, and subseafloor saturation rates. (a) Seismic section below the electrical resistivity tomography (ERT) towing profile (Fig. 1b). The seismic section is extracted from three-dimensional seismic survey data⁵⁹. Two-way travel time of 0.1 s corresponds to a depth of 85–90 m for velocities of 1700–1800 m/s⁵⁹. A magenta rectangular represents an outline of the resistivity model in (b). Green and light blue dashed circles show near-seafloor high amplitude reflections and bottom simulating reflectors (BSRs), respectively. Near-vertical, dark-blue dashed curves indicate the boundaries of seismic blanking zones. (b) Vertical cross-section of the inverted resistivity model below the towing profile. R1–R6 and CD1 are high (> 10 Ωm) and low (< 1.0 Ωm) resistivity zones, respectively. (c) Distribution of gas hydrate (GH)/gas saturation rates. Saturation rates are derived from the subseafloor resistivity values in (b) using Archie’s law. Small black squares and triangles indicate the locations of the head and tail of the towing system of ERT data. Each location of the head and tail is connected by lines. Red and white circles indicate the positions of piston cores with and without GH, respectively, within 150 m of the ERT towing profile³⁸. Green arrows show GH areas inferred from seismic surveys⁵³ (Fig. 1b). Black arrows show discolored seafloor areas detected based on video observations³⁸. Orange arrows show methane plumes zones²¹.