Entropy of geoelectrical time series in the natural time domain
- 1Departamento de Ciencias Básicas, Universidad Autónoma Metropolitana, Av. San Pablo 180, Col. Reynosa, Azcapotzalco, México D. F. 02200, México
- 2National Research Council, Institute of Methodologies for Environmental Analysis, C. da S. Loja, 85050 Tito (PZ), Italy
- 3Departamento de Física, Escuela Superior de Física y Matemáticas, Instituto Politécnico Nacional, Edif. 9, U.P. Zacatenco, 07738, México D.F., México
Abstract. Seismic electric signals (SES) have been considered precursors of strong earthquakes, and, recently, their dynamics have been investigated within the Natural Time Domain (NTD) (Varotsos et al., 2004). In this paper we apply the NTD approach and the chaotic map signal analysis to two geoelectric time series recorded in a seismically very active area of Mexico, where two strong earthquakes, M=6.6 and M=7.4, occurred on 24 October 1993 and 14 September 1995, respectively. The low frequency geoelectric signals measured display periods with dichotomic behavior. Our findings point out to an increase of the correlation degree of the geoelectric signals before the occurrence of strong earthquakes; furthermore, the power spectrum and entropy in NTD are in good agreement with the results published in literature. Our results were validated by the analysis of a chaotic map simulated time series, which revealed the typical characteristics of artificial noise.