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Depth dependence of the frictional behavior of montmorillonite fault gouge: Implications for seismicity along a décollement zone
Author(s) -
Mizutani Tomoyo,
Hirauchi Kenichi,
Lin Weiren,
Sawai Michiyo
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2017gl073465
Subject(s) - montmorillonite , geology , slip (aerodynamics) , pore water pressure , induced seismicity , fault gouge , subduction , mineralogy , fault (geology) , geotechnical engineering , seismology , materials science , tectonics , thermodynamics , composite material , physics
To understand the seismogenic potential of shallow plate‐boundary thrust faults (décollements) in relatively warm subduction zones, water‐saturated Na‐montmorillonite gouges were sheared at a pore fluid pressure of 10 MPa, effective normal stresses ( σ n eff ) of 10–70 MPa, temperatures ( T ) of 25–150°C, and axial displacement rates of 0.03–3 μm/s. The Na‐montmorillonite gouges were frictionally very weak at all conditions tested (steady state friction coefficient μ ss = 0.05–0.09). At T ≤ 60°C, Na‐montmorillonite showed a transition from velocity‐strengthening to velocity‐weakening behavior with increasing σ n eff , whereas at T ≥ 90°C it was largely velocity neutral or velocity strengthening, irrespective of σ n eff . The rates of frictional healing ( β ) showed extremely low values (mostly <0.001) at all temperatures. Our results suggest that the existence of Na‐montmorillonite in the décollement zone at Costa Rica and Nankai promotes aseismic slip, particularly at shallow depths, forming weakly coupled regions.