LOCAL VARIATIONS IN THE GEOMAGNETIC FIELD, HELIUM AND RADON CONCENTRATIONS IN WELLS, AS WELL AS VARIATIONS IN GRAVITY AS POSSIBLE MEDIUM AND SHORT-TERM PREDICTORS OF STRONG EARTHQUAKES ON THE EXAMPLE OF ARMENIA

In order to study the processes in the geological environment during the preparation of strong earthquakes, monitoring was carried out in 1980–1993 on the territory of Armenia for different geophysical fields (geomagnetic, gravitational, geochemical, and radon). The study of changes in the variable geomagnetic field δT was carried out using the ratios of the amplitudes of synchronously measured variations in the components of the δT field in the northern part of Armenia. To assess the change in the state of the geological environment, the calculated parameter N(A) = Ai/Aj, was used, the ratio of the amplitudes of the variations in the geomagnetic field caused by an external source and measured synchronously at different pairs of stations. The calculated parameter N(A) characterizes the change in the electromagnetic induction (electrical conductivity) of the geological environment. Before the Spitak earthquake, the values of the parameter N(A) decreased by about 35%. Analysis of data before the Paravan earthquake also shows a sharp drop in the values of this parameter by 20–25%. Changes in the calculated parameter N(A) show that the electromagnetic induction or electrical conductivity has changed in the studied geological environment. The concentration of subsurface radon at the Jermuk station before the Spitak earthquake increased by 15%, while at the Leninakan station, on the contrary, it decreased. Several months before the Spitak earthquake, mantle helium appeared in the Kajaran well, which usually appears before strong earthquakes. In the northern part of Armenia, where gravity measurements were taken, anomalous changes were also recorded before the Spitak earthquake. The obtained anomalous changes in geophysical fields are possible geophysical precursors of the Paravan (13.05.1986, M = 5.4) and Spitak (07.12.1988, M = 7.0) earthquakes.