ON NONLINEAR AND PARAMETRIC PHENOMENA IN GEOPHYSICAL MEDIA

Experimental studies of nonlinear elastic properties of earth's rocks have been conducted at the seismic station Borovoe (Northern Kazakhstan) and at the testsite Uznozh (Belarus'). Seismic signals were recorded by saisitive broadband strainmeters. The increase of the intensity of seismic noise in Borovoe at arrivals of teleseismic P, S, and surface waves and modulation of the intensity of microseismis by a surface wave were detected. Mechanisms of the nonlinear distortions of microseisms by intense low-frequency signals are considered. Records of strong seismic events contain a constant component, which is due to nonlinear elastic properties of rocks in interise seismic fields. The constant component was studied in experiments with a monochromatic vibrator in Uznozh; it allows the estination of the nonlinearity parameter of the medium, and can make a basis for new methods of seismic microzonation, forecasting ground motions in strong earthquakes and monitoring,