Experimental study on the mechanism of non-synchronism of seismo-electromagnetic radiation precursors

Abstract

In order to investigate the physical mechanism of non-synchronism of seismo-electromagnetic radiation precursors, we have made shear fracture and frictional sliding tests of rock samples by loading them in biaxial compression to model the activity of tectonic fault zones in seismogenic region. By installing antennae of different frequency responses and acoustic transducers around the fracture surface, the signals of electromagnetic radiation and acoustic emission in different directions and of different frequencies produced by rock samples during their shear fracturing and frictional sliding have been recorded by an automatic, high-.speed and continuous observation system. Some implications given by the experimental results are as follows.(1) During the process of shear fracturing and frictional sliding of rock samples under biaxial compression, large amounts of electromagnetic signals are produced; their frequencies range from several hundred Hz to several thousand Hz.(2) Signals received by antennae in different directions and of different frequencies are non-synchronous. They differ in amplitude from one another, with the signal received by antennae nearest to the fracture surface being the maximum.(3) Electric signals and magnetic signals do not appear synchronously; among them, electric signals appear more frequently and are of larger amplitude.The authors hold that electric signals (E) and magnetic signals (M) are of different genetic mechanisms: electric signals from inside the rock sample are produced by the piezoelectric effect of rock-forming crystals and net electric charge produced by the newly created surfaces due to rock fracture, whereas magnetic signals are produced by the high-speed motion of charged rock fragments and the ionization of ambient air excited by electrons emitted by rock in fracturing. Analysis shows that in some moderately strong earthquakes the electric and magnetic signals also showed the phenomenon of non-synchronism: the electric signal was earlier than the magnetic signal. If the same station observes simultaneously the electric field (underground) and magnetic field (air), the efficiency of earthquake prediction by seismo-electromagnetic radiation precursors would be raised effectively.

Impact compressive and bending behaviour of rocks accompanied by electromagnetic phenomena

“…These models include the piezoelectric effect [18], e.g. quartz [19,20], electrification due to the scraping of crack surfaces [21], emission of electrons and charged particles from the fracture surfaces [22], movement of electric charges and so on. However, a complete theoretical explanation has not yet been given for the generation mechanism of electromagnetic phenomena.…”

Statistical Analysis of the Relationship between AETA Electromagnetic Anomalies and Local Earthquakes

“…The electromagnetic signal may be affected by various environmental factors during its propagation. The phenomenon that some observation stations do not respond strongly to observation signals exists in many earthquake detection systems [ 34 ]. It is difficult for stations located in different geographical locations to acquire exactly the same electromagnetic signals.…”