Identification of Changes in the Entropy of Seismic Signals Preceding an Event through Higher Order Zero-crossing Analysis

Abstract

The higher order crossing (HOC) method for signal analysis (Kedem 1986a, 1994), based on the zero-crossing or level-crossing method, provides a useful descriptive and analytical tool that in many respects is analogous to conventional spectral analysis. This analogy has been proven by a series of mathematical theorems that show the potential for complete compatibility between HOC theory and spectral analyses based on the Fourier transform (Hurt 1989; Kedem and Li 1989). Important advantages of the HOC method are its simplicity and remarkable data reduction and information compression capabilities. Published papers in the area of zero-crossing analysis have dealt with signals from a wide range of sources, including communication systems, electronic devices, and bio-physiological phenomena. A few publications have indicated the potential for signal discrimination through a rather simple application of HOC theory, in which a comparison is made among key parameters of the signals (Kedem 1986b, 1994). This has been demonstrated when applied to the field of nondestructive testing (Dickstein et al. 1990, 1991). The power of the technique gave the impetus for application to processing of time domain seismic signals. The HOC method had not been applied to seismic signals before, though zero-crossing analysis had been used in numerous studies on different aspects of seismology such as the discrimination between natural and man-made events (Dergahi-Noubary 1987) or the determination of the arrival time of reflected waves in explosion seismology (Aboutajdine et al. 1981). In the framework of this study, the HOC method of analysis was applied to characterize seismic signals recorded at different times and locations by means of the amount of information that they contain compared to a reference signal. The analyses were then carried out based on real data recorded at six different functioning broadband seismic stations. It was postulated that the amount …