Studies of electromagnetic emission of seismotectonic origin in the Kirghiz S.S.R.

Abstract Continuous observations of electromagnetic emission (EME) have been under way at two sites since 1978 in the Issyk-Kul seismic region, Kirghiz S.S.R., to study anomalous effects of seismotectonic origin. EME is recorded by the method of impulse count using two horizontal magnetic aerials with resonant frequency 15 kHz. The 1978–1981 data series has been analysed statistically to study diurnal and seasonal variations in EME background intensity and their relation to various helio-geophysical phenomena (meteorological and geomagnetic ones). A comparison of EME data and seismicity in the region shows that most of the local earthquakes ( M ⩾ 4.0, R ⩽ 400 km) occurring in the zones of active geological faults are preceded by EME precursors of a few hours to a few days duration. Anomalous effects in EME have also been observed for large and distant earthquakes ( M ⩾ 6.0, R ⩽ 400 km). Mobile measurements have detected increased EME level in active fault zones. These observations can be accommodated within the model of secondary sources in the atmosphere (lower ionosphere) excited by large-scale processes in the crust, particularly at boundaries of blocks and faults.