Depth dependence of the frictional behavior of montmorillonite fault gouge: Implications for seismicity along a décollement zone. Issue 11 (3rd June 2017)

• Record Type: Journal Article
• Authors: Mizutani, Tomoyo; Hirauchi, Ken‐ichi; Lin, Weiren; Sawai, Michiyo
• Is Part Of: Geophysical research letters. Volume 44:Issue 11(2017)
• Page Start: 5383
• Page End: 5390
• Publication Date: 2017-06-03
• Subjects: décollement -- friction -- montmorillonite -- seismicity -- subduction zone; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2017GL073465
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: 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. Key Points: Water‐saturated Na‐montmorillonite gouge has a very low frictional strength at temperatures up to 150°C Temperature has a stabilizing effect on frictional sliding of Na‐montmorillonite under hydrothermal conditions Fluid‐rich, montmorillonite‐rich décollements are unlikely to be nucleation sites for earthquake rupture