Abstract

Nonlinearity and Slow Dynamics in Rocks: Response to Changes of Temperature and Humidity

J.TenCate, T.J.Shankland (Los Alamos National Laboratory, Los Alamos, NM, USA)

e-mail: tencate@lanl.gov

As revealed by longitudinal bar resonance experiments, materials such as rocks and concrete show a wide range of nonlinear elastic behavior. We have examined the time-dependent changes of linear and nonlinear elastic properties of rocks in response to changes in relative humidity (RH) and temperature. A change of RH from 40% to 85% at room temperature causes velocities to drop about a percent in Lavoux limestone; in both Berea and Fountainebleau sandstones the decrease is of order 10%, even though their clay contents differ strongly. After humidity is changed, Young's modulus "creeps" toward a new equilibrium value. Like the slow dynamical response to dynamic strains of order 10.6, the effect is reversible. In contrast, when rocks are subjected to a temperature change of a few degrees, velocity drops by a fraction of a percent, and Q decreases by 10%. Moreover, the sign of the change is negative regardless of the sign of the temperature change. [Work supported by Office of Basic Energy Sciences and the Institute of Geophysics and Planetary Physics, Los Alamos].

Section : 3