Elastic stress indication in elastically rebounded rock

Abstract

It has long been believed impossible to estimate maximum paleo-elastic stress in rocks, because elastic strain disappears by elastic rebound when a rock is sampled. Plastic strain, on the other hand, leaves a permanent change in rocks even after stress is relaxed. For example, calcite records plastic strain as stress-dependent intracrystalline deformation by mechanical twinning. What happens if a rock contains a small amount of calcite bounded by silicate-rich matrix is elastically loaded? To answer this question, we performed a series of triaxial compression tests of sandstones containing calcite particles under the elastic regime. The statistical data show a good correlation between the density of calcite twins in elastically rebounded sandstone specimens and the maximum elastic stress applied. To investigate in detail our experimental results, we used the discrete element method (DEM) to perform a numerical simulation of uni-axial compression tests on sandstone. Our DEM simulation shows the complex distribution of inter-particle forces at each stress level. However, its statistical mean corresponds to the overall force load at the boundary. This simulation result confirms that the statistically averaged calcite twin density can be regarded as a good stress indicator in real sandstones. Copyright © 2011 by the American Geophysical Union.