Observational evidence of non-extensive behavior of seismic coda waves

Abstract

The last decades a lot of progress has been made in studying Earth and planetary Physics based on the science of complexity and the application of generalized formalisms of statistical physics and entropy. Towards this direction, investigation of the dynamical features of seismic waves is of fundamental importance since they could provide information on the statistical properties of the lithosphere.The non extensive statistical mechanics (NESM) seems to be a promising framework for studying complex earthquake systems that exhibit long-range interactions and memory effects. In this work, coda waves are studied from the point of view of non extensive statistical mechanics. Our aim is to demonstrate the applicability of Non extensive statistical mechanics to the fluctuations of coda amplitudes and to define the entropic q parameters obtained in the coda waves recorded by seismological stations in the South Aegean, and generated by three strong earthquake events in the front of the Hellenic Arc.Coda waves are interpreted as scattered seismic waves by heterogeneities in the earth (cracks, faults, velocity and/or density anomalies, etc.). Due to the nature of those scatterers distribution we follow the NESM approach and study the probability distribution functions of the increments of seismic coda waves generated by seismic events recorded in South Aegean and generated by three strong events.We defined the increment function X(t)=V(t+1)−Vt, where V(t) is the measured horizontal ground velocity. We proceed by analyzing the normalized increments X(t) constructing the probability density function PDFp(x), where x=X−XσX, σX being the standard deviation of X(t) and <X> the observed mean value on the same data set. The results of the present work suggests that the seismic coda waves increments deviate from the Gaussian shape and their respective probability density function px could be adequately described by a q-Gaussian with entropic q-values in the range of1.35<q<2.02 with an error of δq=±0.05.This observation implies that seismic coda wave complexity originating by multiscattering effects, can be described by Tsallis entropy terms. The entropic q-values estimated vary along each seismic path for each of the three strong earthquake events analyzed. This observation implies that the value of q is determined by the particular nature of path between the source and the recorded station.