Formation Pore Pressure through the Tuaheni Landslide Complex and the Gas Hydrate Stability Zone at IODP Expedition 372 Site U1517, Hikurangi Margin, New Zealand

IODP Expedition 372 logged, cored, and sampled Site U1517 to gain deeper insight into the nature of the gas hydrate system, the origin of the Tuaheni Landslide Complex (TLC), and any linkages between them. One key parameter required to understand the TLC and the gas hydrate system and to test some of the Expedition hypotheses is an accurate assessment of the in situ pore pressure field. Pore pressure is important as it influences the thickness of the gas hydrate stability zone and the strength of the sediments within and below the TLC. Our initial characterization of pore pressure at Site U1517 integrates one direct pressure measurement and laboratory consolidation experiments. A penetrometer-based pressure measurement at 80 meters below sea floor (mbsf) indicates near-hydrostatic fluid pressure below the base of the TLC and within the gas hydrate stability zone. Ongoing consolidation experiments will provide additional constraints on the in situ pore pressure at 12 depths ranging from 11 to 181 mbsf. This includes pore pressure estimates: (1) above and below a prominent seismic reflection within the TLC that has been preliminarily identified as a horizon that facilitates creep; (2) throughout the gas hydrate stability zone; and (3) beneath the gas hydrate stability zone. These data will be compared with pressure estimates at the base of gas hydrate stability based on the documented temperature profile. Our interpretation of the pressure field at Site U1517 will provide new data for ongoing studies and models on the origin of the TLC and its internal deformation mechanisms, the evolution of the base of gas hydrate stability, and active fluid and heat flow processes that influence gas hydrate system dynamics and may relate to the TLC evolution.