Experimental study of the features of VLF, MF, HF and VHF electromagnetic radiation accompanying rock fracture

In order to investigate the physical mechanism of seismo-electromagnetic signals, many scholars from China and other countries have carried out laboratory and field experiments of rock samples by loading them up to fracture in recent ten-odd years. In each of these experiments, the phenomenon of electromagnetic radiation was observed during the process of rock sample fracture. However, the experimental results can not explain the non-synchronous electromagnetic radiation in actual observation records. In these records, some stations displayed anomalies but some others did not, and the signals of different frequency bands observed by the same station did not occur simultaneously. This has brought about many difficulties to the application of electromagnetic radiation in earthquake prediction. The experimental result of this paper can explain the phenomenon of non-synchronous electromagnetic radiation. In the experiment of this paper, rock samples are uniaxially compressed up to fracture. The antennas of different frequency bands are installed two meters away from the rock sample in different directions. The electromagnetic signals during the whole process of rock sample fracture are recorded synchronously by a 14-channel tape recorder. The experimental results are as follows: (1) signals of the four frequency bands: VLF, MF, HF and VHF, are all recorded during the main fracturing process of rock samples, but signals of different frequencies may somtimes occur non-synchronously; (2) the intensity of electromagnetic radiation is the highest at the moment when the main fracture occurs, but signals in different directions are of different intensities. The above results are consistent with the non-synchronous electromagnetic radiation observed in real earthquakes. It seems possible to predict the orientation of future seismic source by the electromagnetic method of the LF or VLF frequency bands. Contribution No. 95A0075, Institute of Geophysics, SSB, China. The paper is translated by Prof.Jie-Fan HUANG, Peking University from the Chinese into English version.