Nonlinear Processes in Seismic Active Monitoring

Abstract One of the methods used to monitor the development of geodynamic processes in seismically active zones is based on regular sounding of the geological 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 during the radiation and propagation of seismic waves. One of these processes results from peculiarities in the design of different vibrators and their interaction with the ground. Other processes develop in the medium during seismic wave propagation. Such processes enrich the seismic wave field with additional lower and higher frequency components. In this paper, we show that accounting for these processes increases the noise immunity of vibrational correlograms (analogues of explosive seismograms), as well as their time resolution, contributing to more accurate arrival-time measurements of the main wave. Broadening the spectra of the initial seismic signal can result from the seismic nonlinearity of fractured dilatancy regions, which are typical of potential earthquake zones. Here, we show the applicability of seismic nonlinearity as a possible predictive characteristic of the earthquake source development process. Results, analysis, and conclusions presented in this paper are based on numerical calculations and field experiments. The experiments were conducted in parallel with the monitoring of a 355 km long seismic profile during periods of lunar-solar tides. We show that taking into account the amplitude ratios between the multiple and fundamental harmonics of seismic wave fields enables the independence of monitoring results from seasonal and instrumental variations. At the same time, the high sensitivity of these ratios to small stress variations in the Earth’s crust is retained.