Experimental investigation of flash weakening in limestone

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• 作者：Nicola Tisato^a ; ^{nicola.tisato@erdw.ethz.ch} ; Giulio Di Toro^b ; ^c ; ^{giulio.ditoro@unipd.it} ; Nicola De Rossi^d ; ^{derossi@gest.unipd.it} ; Marino Quaresimin^d ; ^{marino.quaresimin@unipd.it} ; Thibault Candela^e ; ^{thibault.candela@ujf-grenoble.fr}
• 关键词：Friction ; Limestone ; Earthquakes ; Powder lubrication ; Flash heating and weakening
• 刊名：Journal of Structural Geology
• 出版年：2012
• 期刊代码：52_01918141
• 类别：ear
• 出版时间：May, 2012
• 卷：38
• 期：Complete
• 页码：183-199
• 文件大小：2815 K

摘要

Flash heating and weakening could operate during earthquake nucleation and propagation. We performed 27 friction experiments in a compression-torsion apparatus on ring-shaped limestone samples at sub-seismic to seismic slip rates 鈮?40聽mm/s, centimetric displacements and normal stresses of 鈮?聽MPa. Friction decreases dramatically at slip rates of 50-150聽mm/s. Flash weakening was contemporaneous with a peripheral temperature rise of 鈭?0聽掳C measured with an infrared camera. The peripheral temperature yields a lower limit to the slipping zone temperature.

The decrease in friction may result from weakening of the asperity contacts due to decarbonation of calcite induced by (1) flash heating or (2) mechanically-activated reactions. However, X-Ray powder diffraction and Raman Spectroscopy analyses do not reveal the presence of decarbonation products in the slipping zone. Instead, White Light Interferometry and Field Emission Scanning Electron Microscope observations reveal the presence of a smooth sliding surface made of nanometric-particles. The mechanical data can be fit by the rate- and state-dependent friction model or by a quadratic model (the latter proposed for powder lubrication). We conclude that flash heating and weakening and powder lubrication may operate together to decrease dynamic friction in limestone in experiments and, for the conditions investigated here, in nature.