[S-CG61] 広域観測・掘削・微視的実験協働沈み込み帯地震の場とメカニズム

[SCG61-P02] Effects of variation of heat flow and thermal history on the consolidation state of incoming sediments at the Nankai Trough

*Hiroko Kitajima¹、Masataka Kinoshita² (1.Texas A&M University, Center for Tectonophysics and Department of Geology & Geophysics、2.University of Tokyo, Earthquake Research Institute)

In subduction zones, sediments on the incoming plate subduct beneath the overlying plate or accrete and underthrust to form accretionary prisms. The evolution of an accretionary prism and the strength of the prism and basal thrust plane are largely affected by the thickness, lithology, and consolidation state of incoming sediments. At the Nankai Trough, while the lithology of incoming sediments is similar across the margin, the heat flow varies across the margin, and anomalously high heat flow (~200 mWm^-2) is observed near the trench off the Muroto Cape and its eastern side (e.g., Yamano et al., 2003; Harris et al., 2013). Such variations in heat flow and thermal history lead to along-strike heterogeneity of sediment properties in a single subduction zone. Here, we investigate the effects of temperature on the consolidation of incoming sediments at the Nankai Trough by conducting basin modeling. Our basin modeling accounts for 1-D consolidation and heat flow and uses shipboard porosity and temperature profiles determined at input sites of scientific ocean drilling programs (i.e., Site C0011 at the Kumano transect, Site 1173 at the Muroto transect, and Site 1177 at the Ashizuri transect) as starting data to model both mechanical and thermally-assisted compaction of sediments as the incoming Philippine Sea plate approaches the trench. We find that porosity at Site 1173 at the Muroto transect, where the anomalously high heat flow near the trench is observed, is lower at the same depth or overburden stress, compared to that at the Kii transect or Ashizuri transect, suggesting that the high heat flow and temperature along the Muroto transect have led to further compaction of the incoming sediments before entering the prism. Porosity from the basin modeling is well consistent with the shipboard porosity measured at scientific ocean drilling programs sites near the trench (Site 1174 at the Muroto transect and Site 582 at the Ashizuri transect), implying that the sediment properties are affected by not only the mechanical overburden and tectonic loading but also by thermal history.