Comparison of frictional strength and velocity dependence between fault zones in the Nankai accretionary complex

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doi: 10.1029/2010GC003442
Author(s): Ikari, Matt J.; Saffer, Demian M.
Author Affiliation(s): Primary:
Pennsylvania State University, Department of Geosciences, University Park, PA, United States
Volume Title: Geochemistry, Geophysics, Geosystems - G<sup>3</sup>
Source: Geochemistry, Geophysics, Geosystems - G>3`, Vol.12. Publisher: American Geophysical Union and The Geochemical Society, United States. ISSN: 1525-2027
Note: In English. 105 refs.; illus., incl. sketch map
Summary: Accretionary complexes host a variety of fault zones that accommodate plate convergence and internal prism deformation, including the decollement, imbricate thrusts, and out-of-sequence thrusts or splays. These faults, especially the decollement and major splay faults, are considered to be candidates for hosting slow slip events and large magnitude earthquakes, but it is not clear what modes of slip should be expected at shallow levels or how they are related to fault rock frictional properties. We conducted laboratory experiments to measure the frictional properties of fault and wall rock from three distinct fault zone systems sampled during Integrated Ocean Drilling Program Expedition 316 and Ocean Drilling Program Leg 190 to the Nankai Trough offshore Japan. These are (1) a major out-of-sequence thrust fault, termed the "megasplay" (Site C0004), (2) the frontal thrust zone, a region of diffuse thrust faulting near the trench (Site C0007), and (3) the decollement zone sampled 2 km from the trench (Site 1174). At 25 MPa effective normal stress, at slip rates of 0.03-100 µm/s, and in the presence of brine as a pore fluid, we observe low friction (µ≤0.46) for all of the materials we tested; however, the weakest samples (µ≤0.30) are from the decollement zone. Material from the megasplay fault is significantly weaker than the surrounding wall rocks, a pattern not observed in the frontal thrust and decollement. All samples exhibit primarily velocity-strengthening frictional behavior, suggesting that earthquakes should not nucleate at these depths. A consistent minimum in the friction rate parameter a-b at sliding velocities of ∼1-3 µm/s (∼0.1-0.3 m/d) is observed at all three sites, suggesting that these shallow fault zones may be likely to host slow slip events.
Year of Publication: 2011
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 16 Structural Geology; 19 Geophysics, Seismology; Accretionary wedges; Asia; Decollement; Earthquakes; Expedition 316; Far East; Fault zones; Faults; Friction; IODP Site C0004; Integrated Ocean Drilling Program; Japan; Leg 190; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; ODP Site 1174; Ocean Drilling Program; Pacific Ocean; Slip rates; Strength; Subduction zones; Velocity; West Pacific
Coordinates: N331300 N331300 E1364300 E1364300
N322000 N322100 E1345800 E1345700
N310000 N350000 E1380000 E1320000
Record ID: 2013046509
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