Laboratory Approach to the Study of Elastic Anisotropy on Rock Samples

Abstract

The experimental approach (hardware and software) to the study of the elastic anisotropy of rocks on spherical samples under hydrostatic pressure up to 400 MPa is discussed. A substantial innovation of the existing measuring system and processing methods enabled us to make a detailed investigation and evaluation of the kinematic as well as dynamic parameters of elastic waves propagating through anisotropic media. The innovation is based on digital recording of the wave pattern with a high sampling density of both time and amplitude. Several options and results obtained with the innovated laboratory equipment are presented.

Crystallographic preferred orientations of exhumed subduction channel rocks from the Eclogite Zone of the Tauern Window (Eastern Alps, Austria), and implications on rock elastic anisotropies at great depths

“…We, therefore, accept that our texture-based predictions of the elastic constants are valid for great depths only. Nonetheless, in order to get an impression on the crack influence at smaller depths, complete P-wave velocity distributions were determined on an amphibolite and an eclogite sample applying the pressure apparatus of the Institute of Geology ASCR, Prague, Czech Republic (Pros et al, 1998). The measurements were performed at various pressure levels starting at ambient conditions (0.1 MPa), the maximum pressures achieved in the experiments (300 and 400 MPa, respectively) are sufficient to close most open microcracks, allowing in particular the judgement of anisotropy differences to the crack-free medium.…”

Linking preferred orientations to elastic anisotropy in Muderong Shale, Australia

“…The elasticity of still-opened pores could depend on pore pressure. Dependencies of elastic wave velocities (and, consequently, elastic coefficients) on pressure usually demonstrate a characteristic behavior described with combination of fast (exponential) and linear increase terms (e.g., Eberhart-Phillips et al, 1989;Pros et al, 1998;Ullemeyer et al, 2011). Attempts were made to explain this trend by two types of pores -soft and stiff -existing in the material (Shapiro, 2003;Pervukhina et al, 2010).…”

Laboratory measurement of elastic anisotropy on spherical rock samples by longitudinal and transverse sounding under confining pressure

“…So far, the directional dependence of velocity anisotropy in spherical samples under hydrostatic pressure of 0.1 MPa up to 400 MPa has been studied only by using P-wave velocity sounding, as described in [24]. This paper deals with a significant improvement of this system, which enables measurements also by using two pairs of perpendicularly oriented shear wave transducers.…”

“…The study of the velocity anisotropy of V P on spherical samples provides more complete information of the velocities in any direction both under atmospheric and high hydrostatic pressures [21][22][23][24][25][26][27][28].…”