Porosity and permeability evolution in the Tuaheni Landslide Complex at Hikurangi margin from IODP Sites U1517 and U1519

ABSTRACT Several mechanisms involving excess pore pressure related to gas hydrate have been proposed to explain active creeping at landslides such as the north Hikurangi margin Tuaheni Landslide Complex (TLC). Cores and logging data were retrieved by the International Ocean Discovery Program (IODP) Expeditions 372 and 375 from the South TLC at Site U1517. Here, the evolutions of porosity, pore structure and permeability are determined to assess the compaction state in the landslide and compare it with that of the undeformed sequence at Site U1519. Although no evidence of gas hydrate in the landslide at Site U1517 was identified by the cruise, zones suspected to host gas hydrates below the landslide or at Site U1519 are characterised by higher porosity, pore diameter and permeability. We show that most of the sedimentary section is in hydrostatic conditions, except the base of the TLC at Site U1517 and a zone below the base of the gas hydrate stability zone at Site U1519. These zones might be candidates for excess pore pressure build-up. There is no obvious evidence of the involvement of gas hydrate in active creeping at the TLC, which is more likely induced by hydrogeomechanical processes.