[S-CG46] Uncovering stress accumulation and fault strengthening of megathrust earthquakes

[SCG46-P07] Poro-viscoelastic properties of Nankai accretionary prism materials: Lab Measurement, Modeling, and Upscaling

*曽根 大貴¹、Jin Zirou¹、Bhagat Kunal¹、Rudraraju Shiva¹ (1.ウィスコンシン大学マディソン校)

キーワード：付加体、異常間隙圧、Poroviscoelasticity、NanTroSEIZE

Disequilibrium compaction, a major cause of overpressures, are typically quantified assuming poroelastic behavior, although it is well-known that sediments also exhibit time-dependent viscous behaviors. We conducted uniaxial-strain creep test on six cores samples recovered from Site C0002 and Site C0024 in the NanTroSEIZE project to observe their poro-viscoelastic behaviors. The observed time-dependent compaction was then modeled using a FEM model with poro-viscoelastic governing equations obeying a Maxwell rheology. Results highlight the transition from undrained to drained creep response, whose timing reflects the duration of overpressure and is governed by the measured permeability (5×10⁻¹⁸ to 2×10⁻²¹ m²) and viscosity. We upscale the problem to plate-margin scale to demonstrate that (1) viscous deformation is an important mechanism that promotes and sustains overpressure, and (2) drainage along faults are important mechanisms operating in accretionary prisms that explains the absence of near-lithostatic pore pressure. We will also discuss the contribution of viscous compaction on the over-consolidation of prism sediments based on lab measured properties.