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.

摘要

已经提出了几种涉及与天然气水合物相关的超孔隙压力的机制来解释滑坡的活跃蠕变，例如北 Hikurangi 边缘 Tuahen 滑坡复合体 (TLC)。国际海洋发现计划 (IODP) 探险 372 和 375 从位于 U1517 站点的南 TLC 检索到岩心和测井数据。在这里，确定孔隙度、孔隙结构和渗透率的演变，以评估滑坡中的压实状态，并将其与 Site U1519 未变形序列的压实状态进行比较。虽然巡航中没有发现 U1517 场地滑坡中存在天然气水合物的证据，但怀疑在滑坡下方或场地 U1519 存在天然气水合物的区域具有较高的孔隙度、孔径和渗透率。我们表明大部分沉积剖面处于静水条件下，除了站点 U1517 的 TLC 底部和站点 U1519 的气体水合物稳定带底部下方的区域。这些区域可能是超孔隙压力积聚的候选区域。没有明显的证据表明天然气水合物参与了 TLC 的主动蠕变，这更可能是由水文地质力学过程引起的。