Constraints on paleo-stress magnitude from triaxial test results and stress inversion analysis of Nankai accretionary prism sediments

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Author(s): Hashimoto, Yoshitaka; Stipp, Michael; Lewis, Jonathan C.; Wuttke, Frank
Author Affiliation(s): Primary:
University of Kochi, Kochi, Japan
University of Innsbruck, Austria
Indiana University of Pennsylvania, United States
University of Kiel, Germany
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 stress magnitude in an accretionary wedge is significant for the understanding of wedge architecture and seismogenic behavior. In this study, we constrained the stress magnitude in the Nankai accretionary wedge using stress orientations from micro-fault inversion and critical state lines of sediments from laboratory experiments. The micro-faults were observed in core samples of the IODP project 'NanTroSEIZE' (Nankai Trough Seismogenic Zone Experiment). At Site C0001 (upper slope site), normal faults and reverse faults were identified in cover sediments and accretionary prism, respectively. At Site C0002 (forearc basin site), reverse, normal and strike-slip faults were observed. We conducted micro-fault inversion to obtain stress orientations and stress ratio for these faults. Triaxial deformation tests were carried out to determine critical state lines. During compaction confining pressure was increased stepwise to ∼400 KPa, ∼700 KPa and ∼1000 KPa at constant fluid pressure of 300 KPa. At each pressure level undrained deformation tests were carried out at an axial displacement rate of 0.01 mm/s. Slopes of the critical state lines varied from 1.1 to 1.6, corresponding to a deviatoric stress vs. effective mean stress (friction coefficient) between 0.55 and 0.80. The stress polygon was used to constrain stress magnitude with the friction coefficient of the sediments from the experiments. A linear relationship of the stress polygon was calculated from stress orientations and stress ratio. The stress magnitude was smaller for normal faults than for reverse faults suggesting changing fault regimes due to stress built-up in the inter-seismic stage and stress drop after the seismic stage.
Year of Publication: 2017
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 16 Structural Geology; Accretionary wedges; Faults; IODP Site C0001; IODP Site C0002; Integrated Ocean Drilling Program; Kumano Basin; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; Pacific Ocean; Paleostress; Pressure; Stress; Tectonics; Triaxial tests; West Pacific
Coordinates: N331400 N331801 E1364301 E1363800
Record ID: 2018096618
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