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Title: Electric earthquake precursors
Alternative title / Subtitle: from laboratory results to field observations
Authors: Βαλλιανάτος, Φίλιππος
Τριάντης, Δήμος Α.
Τζάνης, Ανδρέας
Αναστασιάδης, Κίμων
Σταύρακας, Ηλίας
Item type: Journal article
Keywords: Dry and wet rock specimens;Megascopic scale effects;Macroscopic scale effects;Στεγνά και βρεγμένα δείγματα βράχου;Επιπτώσεις μεγασκοπικής κλίμακας;Επιπτώσεις μακροσκοπικής κλίμακας
Subjects: Science
Issue Date: 5-Apr-2015
Date of availability: 5-Apr-2015
Publisher: Elsevier
Abstract: The generation of transient electric potential prior to rupture has been demonstrated in a number of laboratory experiments involving both dry and wet rock specimens. Several different electrification effects are responsible for these observations, however, piezoelectricity cannot explain why quartz-free rocks can also generate precursory phenomena and electrokinetic phenomena are normally very weak to produce macro- and megascopic scale effects. Electrification is observed in dry, non-piezoelectric rocks meaning that additional, solid state mechanisms should be responsible. Herein we focus on a promising effect that is ubiquitous during brittle rock failure: the motion of charged edge dislocations (MCD) during crack opening and propagation (microfracturing). We report a series of laboratory experiments on dry marble samples and discuss their possible relationship to field observations of purported electric earthquake precursors (EEP). The experiments confirm the generation of pressure-stimulated currents (PSC) as expected by the MCD model. The PSC was linearly related to the stress rate, so long as the stressed material deformed elastically. Deviation from linearity arose when the applied stress drove the specimen into the plastic deformation range; this effect has been attributed to the dependence of the PSC on the stress rate and, ultimately, to the inverse of the changing (decreasing) Young's modulus. The emitted current appears very intense and non-linear just prior to failure, where massive crack propagation implies massive MCD processes. Repeated cycles of deformation are associated with progressively weaker current emission, indicating the strong dependence of electrification on the residual damage. Overall, the results are consistent with, and render support to the concept of electrification by MCD/microfracturing. Other mechanisms cannot be excluded of course but are rather considered to accompany and supplement the drastic MCD process. The experiments cannot determine whether these process can scale up to earthquake-size volumes but they certainly do not contest the possibility. If so, the origin of the EEP would be massive crack formation and propagation, which in the case of earthquakes is expected to be a short-lived process at the terminal phase of the cycle. Observable macroscopic ULF field would be generated by the superposition of fields generated by multiple simultaneous individual cracks and would evolve in correspondence with the crack propagation process. It is possible to model the evolution of large crack ensembles and assess the expected time functions of transient EEP events: the result is a family of asymmetric-bell shaped time functions that may appear isolated or in groups. The model has been successfully applied to the analysis of real field observations.
Language: English
Citation: VALLIANATOS, F., TRIANTIS, D.A., TZANIS, A., ANASTASIADIS, C. & STAVRAKAS, I. (2004). Electric earthquake precursors: from laboratory results to field observations. Physics and Chemistry of the Earth. [Online] 29 (4-9). p.339-351. Available from: [Accessed 10/05/2004]
Journal: Physics and Chemistry of the Earth
Type of Journal: With a review process (peer review)
Access scheme: Publicly accessible
License: Αναφορά Δημιουργού-Μη Εμπορική Χρήση-Όχι Παράγωγα Έργα 3.0 Ηνωμένες Πολιτείες
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