Phase Space Portraits of Earthquake Time Series of Caucasus: Signatures of Strong Earthquake Preparation

Abstract Many studies have been devoted to the statistical analysis of earthquake time series (ETS) in recent years. Modern methods of nonlinear dynamics, applied to ETS, give controversial results: some authors have proved the existence of strange attractors (which means that ETS can be represented by deterministic chaos model), others have demonstrated the absence of such ordered structures. This chapter analyses the spatiotemporal parameters of seismic rate and reveals nonlinear structures in the phase space plots constructed for low seismicity areas, as well as for seismic areas before, during and after the occurrence of the strongest Caucasian earthquakes: Spitak (1988) and Racha (1991). The seismic phase portraits and recurrence plots constructed for different time windows, epicentral distances and magnitude thresholds, reveal some patterns of seismic process dynamics that could be possibly related to precursors of strong earthquakes.