Hydrogeological properties at the Toe of the Nankai Accretionary Prism, using borehole geophysical and petrophysical data within Hole C0024A, Expedition 358 of IODP – NanTroSEIZE Project

• DOI: 10.1190/iceg2021-040.1
• Publication Date: 2021-12-24T07:19:27Z
• Authors: J. Pwavodi; M-L. Doan
• Keywords: Petrophysics; Accretionary wedge; Prism

The Nankai Trough is a locus of slow slips, low frequency, and large-magnitude classical earthquakes. It assumed that high pore pressure contributes substantially to earthquake dynamics. Hence, full understanding the hydraulic regime accretionary prism needed understand this diversity behavior. We contribute by innovatively integrating drilling logging data NanTroSEIZE project. focus on toe studying from hole C0024A drilled intersected décollement at 813 mbsf, about 3 km trench. Pore was first estimated using Eaton's method both sonic velocity data. Both results show follows hydrostatics until top hemipelagites, with local rising up 38% above hydrostatic. Down Hole Annular Pressure monitored during careful reanalysis its variation shows localized inflow fluid formation along borehole. damage zone below decollement especially permeable. zones footwalls are characterized significant porosity permeability values orders magnitude between ∼10−16 10−17 m2 as quantitatively Hvorslev equation for fully penetrating well in confined aquifer. Our fluids getting significantly over-pressurized only few hundred meters décollement. already impermeable across fault, flow channelized zones. It's therefore probable also expected further down tremors slip events.