4:30 PM - 4:45 PM
[SSS29-11] Viscoelasticity of the Nankai accretionary prism: Indentation test on sediments from NanTroSEIZE Expedition 348
Keywords:Viscoelasticity, accretionary prism, Indentation, IODP, Expedition 348
The load/unload-displacement curves indicate that the sediments above ~1200 mbsf show plastic behavior while the sediments below 2000 mbsf show brittle behavior accompanied by a sudden drop in stress due to the formation of radial fractures. The yield stress increases with depth from a few MPa at 870 mbsf to ~40 MPa at 3000 mbsf. The Young’s modulus of the sediments increases from ~0.1 GPa at 870 mbsf to ~1.5 GPa at 2000 mbsf, then it becomes nearly constant at ~1.5 GPa below 2000 mbsf. The change of mechanical behavior most likely reflects the sediment consolidation because porosity gradually decreases from ~60% at seafloor to ~30% at 1500-2000 mbsf, then reaches to ~18% at 3000 mbsf. The plastic-brittle transition may appear between 1500 mbsf and 2000 mbsf. The strain energy for the Nankai earthquakes could be accumulated mainly in the sediments below 2000 mbsf.