[1] Laboratory and field observations note the significant role of strength recovery (healing) on faults during interseismic periods and implicate pressure solution as a plausible mechanism. Plausible rates for pressure solution to activate, and the magnitudes of ultimate strength gain, are examined through slide-hold-slide experiments using simulated quartz gouge. Experiments are conducted on fine-grained (110 mm) granular silica gouge, saturated with deionized water, confined under constant normal stress of 5 MPa and at modest temperatures of 20 and 65°C, and sheared at a maximum rate of 20 mm/s. Data at 20°C show a log linear relation between strength gain and the duration of holding periods, whereas the higher temperature observations indicate higher healing rates than the log linear dependencies; these are apparent for hold times greater than $1000 s. This behavior is attributed to the growth and welding of grain contact areas, mediated by pressure solution. The physical dependencies of this behavior are investigated through a mechanistic model incorporating the serial processes of grain contact dissolution, grain boundary diffusion, and precipitation at the rim of contacts. We use the model to predict strength gain for arbitrary conditions of mean stress, fluid pressure, and temperature. The strength gain predicted under the experimental conditions (s eff = 5 MPa and T = 65°C) underestimates experimental measurements for hold periods of less than $1000 s where other frictional mechanisms contribute to strength gain. Beyond this threshold, laboratory observations resemble the trend in the prediction by our mechanistic model, implicating that pressure solution is likely the dominant mechanism for strength gain. The model is applied to the long-term prediction of healing behavior in quartzite fault zones. Predictions show that both rates and magnitudes of gain in contact area increase with an increase in applied stresses and temperatures and that fault healing aided by pressure solution should reach completion within recurrence interval durations ranging from <1 to $10 4 years, depending on applied stresses, temperatures, and reaction rates.

No abstract

Background and Purpose-The effect of ebselen, a seleno-organic compound with antioxidant activity through a glutathione peroxidase-like action, on the outcome of acute ischemic stroke was evaluated in a multicenter, placebo-controlled, double-blind clinical trial. Methods-Patients diagnosed as having acute ischemic stroke who could receive drug treatment within 48 hours of stroke onset were enrolled. Oral administration of ebselen granules suspended in water (150 mg BID) or placebo was started immediately after admission and was continued for 2 weeks. The major end points were the Glasgow Outcome Scale scores at 1 month and 3 months after the start of treatment. The modified Mathew Scale and modified Barthel Index scores at 1 month and 3 months were also studied as secondary outcome measures. Results-Three hundred two patients were enrolled in the trial. Intent-to-treat analysis of 300 patients (151 given ebselen and 149given placebo) revealed that ebselen treatment achieved a significantly better outcome than placebo at 1 month (Pϭ.023, Wilcoxon rank sum test) but not at 3 months (Pϭ.056, Wilcoxon rank sum test). The improvement was significant in patients who started ebselen within 24 hours of stroke onset but not in those who started treatment after 24 hours. There was a corresponding improvement in the modified Mathew Scale and modified Barthel Index scores. Conclusions-Early treatment with ebselen improved the outcome of acute ischemic stroke. Ebselen may be a promising neuroprotective agent. (Stroke. 1998;29:12-17.)