TO THE PROBLEM OF INVESTIGATION OF ABNORMAL APPEARANCE OF SEISMIC IMPACTS IN NEAR-SOURCE AND NEAR-FIELD ZONES OF STRONG EARTHQUAKES

Abstract

Geological medium of wavefield propagation is characterized by geometrical divergence and absorption of elastic waves. The main factors influencing the level of seismic effect at the observation point are geological structure of a 30m «engineering» layer of soil, the presence of a variety of inclusions and their power, and the density and porosity of ground rocks saturated with different fluids. At the same time, comparison of seismic data with the geological structure of the region during the strong earthquakes in 1985 (Mexico) and 1988 (Armenia) shows that the cause of the observed effects of amplification of the seismic action at considerable distances from the epicenters, was resonant amplification of the amplitude in the upper soil part of several hundreds of meters. It should also be noted that the effects of changes of observed seismic effect are associated with both the intensity of the wave field (geometric nonlinearity), and with geological and geophysical properties of the medium (the physical nonlinearity).