Temperature Dependence of Strength of Rocks under High Confining Pressure -Micromechanism and Implications-

Abstract

乾燥花嵐岩に対し封圧1500MPa下での3軸試験が, 細かい温度間隔で600℃まで, 平均ひずみ速度2×10-6s-1で行われた。実験は, 圧縮強度が摩擦強度に等しくなるときに起こる, 高圧型破壊領域で行われた。強度は温度の増加とともに減少し, 250℃近くでは異常に低下した。微細機構観察から, この強度の異常な低下は, 温度あ増加につれて, クラック群の卓越からその抑制と結晶塑性の卓越への変化であることが示唆された。この結果は, 地殻の地震発生層の脆性一延性仮説に対する新しい解釈を与える:すなわち, 地震は強度が低いところでより発生あるいは核形成し易いことを示唆する。

Triaxial testing on a dry granite was conducted at a confining pressure of 1500 Mpa and temperatures to 6000C in small temperature intervals with an averaged strain rate of ap‐ proximately 2 x 106 s'. All the experiments fall in the high‐pressure type fracture regime, which occurs when the compressive strength equals the frictional strength. The strength of the granite decreases with increase of temperature but it is unusually low at around 2500C. Micromechanical studies suggest that such behavior is caused by switching the dominating factors from the activation of crack groups to the inhibition of them and the dominance of crystalplasticity with increase of temperature.These results suggest to provide an alternative explanation for the brittle‐ductile hypothesis of the seismogenic zone in the crust: earth‐quakes could occur or nucleate more easily where the strength is