The nonlinear processes in active monitoring

Abstract One of the methods used to monitor the developing geodynamic processes in seismically active zones is based on regular sounding of the medium by powerful seismic vibrators, with subsequent analysis of the time dynamics of the seismic field parameters. Such monitoring is accompanied by some nonlinear processes taking place at the stages of radiation and propagation of seismic oscillations. One is due to the peculiarities of constructions of different vibrators and the processes of its interaction with the underlying surface. Others develop in the medium of seismic wave propagation. Such processes enrich the seismic wave field with additional lower and higher frequency components. In this chapter it is shown that allowance for these processes increases the noise immunity of vibrational correlograms (analogs of explosive seismograms), as well as their time resolution, contributing to an increase in the accuracy of measurements of the arrival types of the main wave types. The modern concept of earthquake source development is as a process of the development of a system of cracks. Broadening of the spectra of the initial sounding seismic oscillations also results from vibroseismic sounding of fractured dilatancy media typical for earthquake preparation zones. The applicability of the parameters of wave field nonlinearity in the form of possible prognostic characteristics of the earthquake source development process is justified. The results of an analysis and formulated conclusions presented in this chapter are based on numerical calculations and experiments. The experiments were made during monitoring of a 355-km-long Earth’s crust zone in periods of lunisolar tides. It is shown that allowance for the ratios between the high and first harmonics of seismic wave fields provides invariance of positive results of monitoring with respect to inevitable seasonal and instrumental fluctuations of the intensity characteristics of the radiation field. At the same time, high sensitivity of the relations to small variations of stresses in the Earth’s crust is retained.