5:15 PM - 7:15 PM
[SSS10-P16] Evaluation of fluidization during earthquake slip at the primary slip zone in the Neogene accretionary complex, Boso Peninsula, Japan
Dynamic fault weakening during earthquake slip on a fault affects the slip behavior. For example, at the 1999 Chi-Chi earthquake in Taiwan and the 2011 Tohoku-Oki earthquake, thermal pressurization (TP) was considered to occur on their faults, which could enhance the rupture propagation and could resultantly increase the amount of fault slip. In the case that the rupture reaches the trench, a large uplift of the seafloor might trigger huge tsunami. Therefore, it is significantly important to elucidate the dynamic weakening mechanism on their faults. In this study, we focus on the primary slip zone (PSZ) in the Neogene Hota Group, the Boso Peninsula in which TP is considered to function on the fault on the basis of its geochemical analyses and modellings. we performed the field investigation, collection of the fault samples, microscopic observation, and spatial analysis of major elements by using an electron probe micro-analyzer. In the PSZ, grain-size reduction and developments of layered and/or flow structures are characteristics by comparing with each surrounding rocks. Because the flow structure may form during fluidization related to earthquake events, we performed the numerical analysis to determine the fundamental parameter of fluid dynamics such as the Reynolds number, and estimated the viscosity to be 1.68×10-3. This could indicate that turbulent flow occurred in the PSZ during earthquake slip. In addition, the fluidization in the slip zone may enhanced pore-fluid pressure that may assist the function of TP.