5:15 PM - 7:15 PM
[SCG55-P12] Evaluations of physical properties and pore-fluid pressure in core samples from Site C0023, IODP EXP370
Keywords:Nankai Trough, decollement zone, pore-fluid pressure
Recent seismological and geodetic observations suggested that high pore-fluid pressures within the Nankai accretionary prism and plate-subduction zone are strongly related to the generation of slow earthquakes. Here we focus the décollement zone within the Nankai Trough off the Muroto Peninsla, and evaluate the pore-fluid pressure on the basis of core-sample physical properties. We used the data, published by IODP EXP370 C0023, and investigated the depth profiles of wet bulk density, porosity, and Vp. The depth variation of wet-bulk density increased from 1.9 g/cm³ to 2.3 g/cm³ within the depth range of 204.115 to 1176.67 m. However, a slight decrease from 2.2 g/cm³ to 2.1 g/cm³ in the décollement zone was detected. Vp data showed an increasing trend from 3.1 km/s to 4.3 km/s within the same depth range. However, it remained relatively constant within the range of 3.5 to 3.7 km/s in the décollement zone. Furthermore, the pore-fluid pressure in the sediments, estimated by using the equation Pf=P0+gz0zρbulkz'dz' proposed by Hubbert et al. (1959), showed the increment from 52 MPa to 75 MPa within the depth range of 204.115 to 1176.67 m, which corresponds to excess pore-fluid pressure across the entire depth region. In addition, we calculated the pore-fluid pressure ratios that ranging from 0.48 to 0.67. These values are consistent with previous research by Tsuji et al. (2008), which reported a range of 0.4 to 0.7. In the presentation, we will focus the discussion on the mechanisms of pore-fluid pressure increment on the basis of consolidation theory.