Laboratory Study of Rock Deformation and Fracture

Abstract

Our primary interest lies in the physics of electromagnetic phenomena associated with deformation and fracture of rocks. We start with a brief review of laboratory study of electromagnetic fields resulted from acoustic waves and shock polarization and magnetization effects in different materials. The vibration of charged dislocations and piezo-galvanic effect are considered to explain this effect in metals whereas the production and mobility of point and linear defects of atomic lattice is treated as a possible cause for the shock polarization effect in dielectrics. We discuss briefly a variety of electromagnetic phenomena caused by rock fracture. Among them are radiowave, optical and -radiation, and electron and ion emissions from fracturing rocks. We study the theories explaining the generation of strong electric fields in cracks and collapsing pores.Keywords Dislocation • Piezo-galvanic effect • Point defect • Rock fracture • Shock magnetization • Shock polarization Electromagnetic Effects Caused by Dynamic Deformation of a SolidIt is common knowledge that the dynamic deformation and fracture of solids are accompanied by a great variety of electromagnetic effects. The basic characteristics of these phenomena depend on the scales of fracture, intensity and duration of stress and strain, and a number of other factors. Such effects as generation of lowfrequency electromagnetic fields and radiowaves, emission of charged particles, light flashes, X -ray emission and micro-discharges inside of cracks have been observed in laboratory experiments (e.g., see Parrot 1995; Surkov 2000). It has been found experimentally that shock compression of different solids gives rise to a jump of electric potential at the shock front in all kinds of materials: metals, semiconductors, and dielectrics (e.g., Mineev and Ivanov 1976; Freund V. Surkov and M. Hayakawa, Ultra and Extremely Low Frequency Electromagnetic Fields, Springer Geophysics, DOI 10.1007/978-4-431-54367-1__9, © Springer Japan 2014 335 336 9 Laboratory Study of Rock Deformation and Fractureand Pilorz 2012). Effects of shock magnetization and demagnetization have been observed in magnetic materials. Fragments of fractured solid, as a rule, carry electric charges. The rock deformation and fracture can explain, in principle, some features of electromagnetic perturbations arising from large-scale tectonic processes such as EQs, volcanic eruptions and deeply buried high-yield detonations. In this section we first review laboratory studies and then examine these electromagnetic phenomena by analyzing the basic physical processes at microscopic level. Sometimes we will need to extend our research field to the frequency range of several MHz to gain a better insight into underlying mechanisms of these phenomena.

Comparative Assessment of Criticality Indices Extracted from Acoustic and Electrical Signals Detected in Marble Specimens

“…Besides the transient elastic waves mentioned above, it has been verified experimentally that during mechanical loading of some classes of brittle material, mechanisms are activated which are responsible for the generation of electromagnetic emissions [6]. These emissions are nowadays considered as potential tools for SHM purposes [25,26].…”

“…Nowadays, the most widely used SHM tools are based on the detection and recording of either acoustic [1][2][3] or electric [4][5][6][7] signals, emitted while structural members are loaded by mechanical stimuli. The proper interpretation of the data acquired by these sensing techniques, in the direction of revealing hidden pre-failure indicators, is among the challenges of the current scientific research [8,9].…”