Experimental investigation on poro-elasto-plastic behavior of the inner accretionary wedge sediments at the nankai subduction zone

Author(s): Kuo, Szu-Ting; Kitamura, Manami; Kitajima, Hiroko
Author Affiliation(s): Primary:
Texas A&M University, College Station, TX, United States
Other:
National Institute of Advanced Industrial Science and Technology, Japan
Volume Title: AGU 2017 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2017; American Geophysical Union 2017 fall meeting, New Orleans, LA, Dec. 11-15, 2017. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) have installed borehole observatories to monitor the evolution of physical and hydrological properties caused by crustal deformation at various strain rates within earthquake cycles. The observatories have been installed at the base of a forearc basin above the megathrust fault (Site C0002) and near the shallow tip of the megasplay fault (Site C0010), and will be installed near the frontal thrust (Site C0006) next year. The observatory pore pressure data have shown the dynamic and post-seismic responses and are used to estimate volumetric strain (deformation) with poroelastic parameters (e.g., Wallace et al. 2016). The parameters of submarine sediments are often computed theoretically from the porosity, compressibilities of matrix, solid, and pore fluid; however, few direct constraints on core samples have been made. To investigate the poro-elasto-plastic behavior of submarine sediments, triaxial experiments with stress relaxation were conducted on the claystone cores (20% porosity) from ∼2185 meters below sea floor at Site C0002. Triaxial tests were conducted by applying an axial load at a constant displacement rate of 5×10-9 m/s, while keeping confining pressure (Pc) at 42, 48, or 78 MPa and pore pressure (Pp) at 20 MPa. Stress relaxation tests were conducted periodically, in which neither axial displacement nor pore volume change was allowed. At lower effective pressure (Pe=Pc-Pp) of 22 and 28 MPa, the samples deform in a brittle manner, with a peak strength of 50 and 55 MPa and a residual strength of 36 and 46 MPa, respectively. At higher Pe of 58 MPa, the sample exhibits strain hardening. The relaxation tests at Pe=22 MPa show an increase in Pp before yield and a decrease in Pp after yield, suggesting a transition from compaction to dilation. All of the relaxation tests at Pe=58 MPa show an increase in Pp, suggesting compaction throughout the deformation. The ratio of Pp to volumetric strain determined from the relaxation tests ranges 0.4 - 2.0 kPa/µ strain and is lower than the value of 8.7 kPa/µ strain for sediments with 20% porosity computed based on the poroelasticity theory (Davis et al., 2009), implying that the volumetric strain during our relaxation tests is mainly due to plastic deformation.
Year of Publication: 2017
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; IODP Site C0002; IODP Site C0006; IODP Site C0010; Integrated Ocean Drilling Program; Kumano Basin; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; Pacific Ocean; West Pacific
Coordinates: N331800 N331801 E1363801 E1363800
N331236 N331236 E1364112 E1364112
N330100 N330200 E1364800 E1364700
Record ID: 2019016164
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