A theory of rock core-based methods for in-situ stress measurement
© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB. 2009
Received: 2 November 2004
Accepted: 5 July 2009
Published: 30 November 2009
The behavior of the inelastic strain of rocks under the loading of compression reflects the history of stresses applied to the rocks. A number of methods based on this rock property of stress memory have been proposed for measuring in-situ stress. The magnitudes of in-situ stress can be determined from drilled core samples by deformation rate analysis (DRA); in other words, rocks do have the property of in-situ stress memory. In general, the inelastic strain of rocks increases with an increase in applied stress difference. The Keiser effect observed in laboratory experiments is explained as the behavior of the inelastic strain of this well-known mode. However, this effect cannot be the mechanism of the in-situ stress memory because the effect does not potentially allow us to determine the magnitudes of previously applied stress. Here, I theoretically show that rocks exhibit another mode of inelastic strain under axial loading of compression—if locally concentrated stresses in rocks relax to some extent under in-situ stress at depth. The magnitudes of in-situ stress can be determined from the behavior of this mode of inelastic strain under axial loading. The results of DRA suggest that this hypothesis is actually valid and that it is not only valid for the DRA, but also for the other rock core-based methods used for measuring in-situ stress.