V. Cuomo et al., On the time dynamics of geoelectrical signals recorded in a seismic area of Southern Apennine Chain (Italy), PHYS CH P A, 25(3), 2000, pp. 227-232
Citations number
21
Categorie Soggetti
Earth Sciences
Journal title
PHYSICS AND CHEMISTRY OF THE EARTH PART A-SOLID EARTH AND GEODESY
In this work we analyse the hourly geoelectrical time series recorded by me
ans of three stations located in a seismically active area of Southern Apen
nine Chain (Italy): Tito station (January 1992 - December 1997), Tramutola
station (January 1995 - December 1995) and Giuliano station (January 1996 -
December 1997). The time dynamics of the geoelectrical time series was inv
estigated to obtain information regarding: i) the stochastic or chaotic beh
aviour of the time series; ii) the presence of scaling laws in their power
spectral density and the estimation of the power-law index; iii) the possib
le correlation between the temporal variation of the power-law index and th
e local seismic activity. Autoregressive models and the Lomb Periodogram me
thod have been applied to get the most quantitative information about the t
ime dynamics from geoelectrical signals. Firstly, the predictability of geo
electrical measurements has been investigated using autoregressive models.
The procedure is based on two forecasting approaches: the global and the lo
cal autoregressive approximation. The comparison of the predictive skill of
the two techniques is a strong test to discriminate between low-dimensiona
l chaos and stochastic dynamics. Our findings suggest that the physical sys
tem governing the electrical phenomena in active seismic areas is character
ized by a stochastic dynamics. In a second step we investigated the stochas
tic properties of the geoelectrical signals searching for scaling laws in t
he power spectral density, identifying for it a power-law P(f)proportional
to 1/f(alpha), with the scaling exponent alpha being a typical fingerprint
of fractional brownian processes. In this analysis we apply the Lomb Period
ogram method, which allows to calculate the power spectral density for time
series with missing data. Finally the possible correlation between the tim
e fluctuations of power-law index and the local seismic sequences has been
investigated. An interesting coseismic variation of the scaling exponent in
power spectra of geoelectrical time series recorded at Tito station has be
en identified on April 3, 1996. During the same period significant anomalou
s patterns are indentified in geoelectrical time series measured at Giulian
o and Tramutola stations. (C) 2000 Elsevier Science Ltd. All rights reserve
d.