Rapid postseismic strength recovery of Pingxi fault gouge from the Longmenshan fault system: Experiments and implications for the mechanisms of high‐velocity weakening of faults

Abstract

[1] Slide-hold-slide tests were conducted on gray blackish gouge (GBG) and yellowish gouge (YG) from Pingxi fault zone to see how rapidly the strength of Longmenshan fault recovers after the 2008 Wenchuan earthquake. Twenty dry runs were made at a normal stress of 0.8 MPa, at a seismic slip rate of 1.4 m/s, and with hold time t h ranging 0.3-10 5 s. Results exhibit very rapid healing by more than 0.4 in friction coefficient μ in less than 5-10 s, followed by gradual healing in proportion to log(t h ). Healing rates, (increase in μ)/(log (t h )), during rapid and slow healing are 0.188 and 0.015 for GBG and 0.154 and 0.016 for YG, respectively. The average temperature in the outer half of a 5 μm thick slip zone decreases from 260-300°C to 110-170°C in 5-10 s, and hence, temperature drop appears to be correlated with the rapid healing. Previously reported rapid healing at subseismic slip rates (85-90 mm/s) begins to occur in 10-300 s after the stop of sliding, and this cannot be explained by the cooling of gouge. The difference in healing between subseismic slip rates (delayed and rapid healing) and seismic slip rates (immediate and rapid healing) suggests that the dominant weakening mechanism shifts from tribochemical processes at subseismic slip rates to frictional heating at seismic slip rates. Slip-zone structures are too complex and variable from run to run to reveal microscopic mechanisms for the strength recovery. Rapid healing following seismic slip can be a cause for reduced aftershocks along major coseismic faults.Citation: Yao, L., T. Shimamoto, S. Ma, R. Han, and K. Mizoguchi (2013), Rapid postseismic strength recovery of Pingxi fault gouge from the Longmenshan fault system: Experiments and implications for the mechanisms of high-velocity weakening of faults,

Initiation, movement, and run-out of the giant Tsaoling landslide — What can we learn from a simple rigid block model and a velocity–displacement dependent friction law?

“…The U layers consisted of ultrafine grains that were mostly less than 1 μm in diameter and appeared to be welded or sintered. Similar textures were reported previously (Sawai et al, 2012;Togo and Shimamoto, 2012;Yao et al, 2013aYao et al, , 2013b. These highly deformed zones consisting of ultrafine grains may be slip zones in which the shear deformation was concentrated.…”

“…Single or overlapping stratified structures of the U layer, CCA-bearing layers, and CCA-free layers were observed in air-dried samples and wet samples after large shear displacements (Boutareaud et al, 2010;Ferri et al, 2011;Han and Hirose, 2012;Sawai et al, 2012;Yao et al, 2013aYao et al, , 2013b. In conclusion, the microstructures of our sheared semi-wet fault gouges are similar to those of the dry samples.…”

Shear‐Rate‐Dependent Behavior of Clayey Bimaterial Interfaces at Landslide Stress Levels

“…Studies on the shear behavior of bimaterial interfaces between soil and concrete, steel, geotextiles, and other manufactured materials, especially under low normal stresses ( σ n = 1–100 kPa), are abundant in the literature (e.g., Boukpeti & White, ; Eid et al, ; Ganesan et al, ; Ho et al, ; Lemos & Vaughan, ; Potyondy, ; Tsubakihara & Kishida, ; Wijewickreme et al, ; Zhang & Zhang, ). Equally, in fault mechanics, many researchers have been focusing on the slip‐ and rate‐dependent behavior of rock interfaces and thin gouge layers under high normal stresses ( σ n = 1–20 MPa) to understand the behavior of faults under subseismic and coseismic slip rates (e.g., Di Toro et al, , , ; Hirose & Shimamoto, ; Perfettini & Ampuero, ; Kitajima et al, ; Togo et al, ; Yao et al, , Ma et al, ; Yao et al, ). On the other hand, the rate‐dependent behavior of soil‐rock interfaces (e.g., Suzuki et al, , ) at typical landslides stress levels has received lesser attention.…”

A rotary-shear low to high-velocity friction apparatus in Beijing to study rock friction at plate to seismic slip rates

“…The ultrafine-grained zones are composed of ultrafine particles mostly less than 1 lm in size similar to those reported in Fig. 5d and j in Yao et al (2013b), and we interpret them as slip zones accommodating fault slip. The particles gradually coarsen from an ultrafine-grained layer to the coarser-grained layer forming a slip-zone unit.…”