[H-DS18] 海底地すべりとその関連現象

[HDS18-P04] 南海トラフにおける海底地すべり堆積物の帯磁率異方性について

*北村 有迅¹ (1.鹿児島大学大学院理工学研究科地球環境科学専攻)

キーワード：海底地すべり堆積物、帯磁率異方性解析、付加体

We review the results of magnetic fabric analysis in the sediments recovered in the Nankai subduction margin off the Kii Peninsula, Japan using the anisotropy of magnetic susceptibility measurements. Samples were taken from the cores at IODP Sites C0011 and C0012 recovered during IODP Expeditions 322 and 333, which retrieved sediments from the seafloor to just above the basalts. The samples exhibit different behavior from those expected for undeformed deep-sea sediments. The degree of anisotropy of the magnetic ellipsoids is small and constant from the surface down to ~250 and ~80 mbsf at Sites C0011 and C0012, respectively. The flattening parameter F start increasing with depth in Unit II indicating flattening in the lower units. A zone of anomalously constant porosity is noted in the upper portion of the sites. These observations suggest that compaction is obstructed in the shallow sediments. This supposedly rigid sediment interval may influence the initiation of deformation when the sediments reach the deformation front. Such pre-existing heterogeneity may be one constraint on the deformation along the plate boundary from the trench through the seismogenic zone.