Frictional experiments of dolerite at intermediate slip rates with controlled temperature: Rate weakening or temperature weakening?

A rotary shear apparatus has been newly set up in Chiba University which can control the temperature near a sliding surface, T_meas, up to 1000°C independently from slip rate, V. Frictional experiments at 0.010 m/s, 1 MPa normal stress, and variable T_meas for dolerite have revealed a remarkable effect of temperature on the friction coefficient, f. With increasing T_meas, f starts from 0.7 to 0.8 at room temperature (RT), decreases down to 0.5–0.6 at 400°C, increases until 800°C, and then decreases again. We have also conducted XRD analyses of the wear materials (mainly submicron particles) and investigated microstructures of the sliding surfaces developed at different temperatures T_meas, and we found that there is a negative correlation between f and the amount of amorphous material except at RT and 1000°C. The generation of the amorphous phase probably causes the weakening. There is no amorphous phase recognized for a sample at 1000°C which is an aggregate of rounded crystals. EBSD analyses show that the material on the sliding surface at 1000°C contains randomly oriented hematite grains, which together with the observed microstructural features suggests that granular flow was taking place. We have also demonstrated that f depends not only on the instantaneous value of temperature, but also on its history. By comparing with conventional rotary shear friction experiment for the same dolerite without temperature control, we conclude that strong “rate weakening” as recently observed in high-velocity frictional experiments without an active control of the temperature has a significant amount of contribution from the temperature effect

Anelastic strain recovery reveals extension across SW Japan subduction zone

Sediment dominated convergent margins typically record substantial horizontal shortening often associated with great earthquakes. The convergent margin south of Japan is arguably one of the most extensively investigated margins and previous studies have documented extensive evidence for accretion and horizontal shortening. Here, we show results from anelastic strains recovered from three partially lithified sediment samples (40~ porosities) across the southwest Japan accretionary prism and propose that the margin is dominated by horizontal extension rather than compression. The anelastic strain results are also consistent with stress directions interpreted from two independent techniques - bore hole breakout orientations and core-scale fault data. We interpret this unexpected result to reflect geologically recent underthrusting of a thick sediment package and concomitant weakening of the decollement

Coseismic dehydration of serpentinite: Evidence from high-velocity friction experiments

High-velocity friction (HVF) experiments on serpentinite under conditions equivalent to large amounts of earthquake slip produced large volumes of water vapor derived from the frictional-heating-induced dehydration of serpentinite. Fourier Transform Infrared (FTIR) and thermogravimetry (TG)-Differential Scanning Calorimetry (DSC) microspectroscopic analyses show that the water in the slip zone and its bounding zones was released due to dehydration during the HVF experiments. Our experimental results demonstrate that (i) the run product consists of ~ 10 wt.% molten materials with abundant vesicles and ~ 90 wt.% fine-grained clasts; (ii) both serpentine and olivine minerals were melted during high-velocity slip (1.1–1.3 m/s); (iii) rapid serpentine dehydration occurred in a zone of up to ~ 3 mm wide, including the slip zone and its bounding zones, accompanying frictional melting during high-velocity slip; and (iv) no distinct dehydration or frictional melting occurred during low-velocity slip (< 0.4 m/s). These findings show that dehydration reactions of serpentine can be caused by frictional heating that accompanies frictional melting in the slip zone, and by the rapid diffusion of frictional heat from the main slip zone to a wide zone bounded by the coseismic slip plane during seismic faulting. The present results reveal that the thermal pressurization caused by the dehydration of serpentine and frictional melting is a main mechanism that may lead to the dynamic weakening of seismogenic faults, thereby facilitating seismic slip during large earthquakes in subduction zones and along intracontinental faults that contain abundant hydrous minerals

The effect of dynamic recrystallization on olivine fabric and seismic anisotropy: Insights from a ductile shear zone in the Oman ophiolite

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Effects of dissolution-precipitation processes on the strength and mechanical behavior of quartz gouge at high-temperature hydrothermal conditions.

Laboratory experiments on simulated quartz gouges at a temperature of 927°C, a confining pressure of 300 MPa, and a pore water pressure of 200 MPa demonstrate the interactions between cataclastic and dissolution-precipitation processes and their effect