Not only geophysical observations, but also geologic observations of the fault are also important to understand the physical mechanism of diverse slip behavior. Recent IODP drilling projects aim to get core from the shallow plate interface, where slow earthquake occurs. I take part in the project in Nankai subduction zone, and analyze drilled cores and their physical property data.

① Physical Property data ： Yabe et al. (2019, EPS)

Physical properties (such as density, porosity, Vp) are measured for drilled cores. Correlations among those physical properties reflect the compaction state of the material during the accreted process. Hence, quantitative understanding of those relations can promote understanding of the evolution history of the accretionary prism.

② XCT data： Yabe et al. (2019, EPS)

All cores drilled by D/V "Chikyu" are scanned by the XCT as soon as the core acquisition.Because CT values are mainly dependent on the density in the sediment, and because density is correlated with other physical properties, XCT data should be able to provide 3D distributions of physical properties. For example, focusing around the fault in the core, such information can be incorporated into the numerical simulations of the fault rupture.

③ Geologic observations of the shear zone

Several previous studies investigated the shear zone in the core, and presented evidences of coseismic rupture. However, many other shear zones are still included in the cores, which are remained to be analyzed. Investigations on the many shear zone in the shallow accreted prism will promote understanding of universal deformation mechanism of the shallow accretionary prism. Deformation mechanism of the shallow accretionary prism affects the generation of Tsunami, which is a important issue for seismic hazard assessment.