S. Leonardi et Hj. Kumpel, SEARCH FOR STRANGE ATTRACTORS IN MAGNETIC-FIELD DATA - AN EXAMPLE FROM A TERTIARY VOLCANIC AREA NEAR BONN, GERMANY, Journal of geodynamics, 21(4), 1996, pp. 329-338
Spatial variations of the magnetic field, measured at the Earth's surf
ace, are mainly due to geological inhomogeneities within the crust. Th
e present state of the crust, in turn, reflects its past dynamical pro
cesses and evolution. We analyzed the magnetic field intensity along a
few but densely sampled profiles in a Tertiary volcanic province near
Bonn, Germany. The aim was to find out whether the variation of the m
agnetic intensity can be related to a deterministic, although chaotic,
generating system or to a stochastic one. In the former case, the geo
dynamical history would depend on a few degrees of freedom, whereas in
the latter case, the parameters to take into account were so many tha
t a statistic approach appears to be more suitable. Since strange attr
actors do not emerge from the analyzed data, we exclude the presence o
f a chaos generating system. Autocorrelation functions and a rescaled-
range analysis, on the other hand, reveal and quantify a certain degre
e of correlation among successive data points and allow calculation of
a range of spectral exponents in log-log diagrams, which are clearly
distinct from those of white noise and Brownian motion. Only one of th
e profiles exhibits similarity to uncorrelated or white noise. In this
case, the signal variations do not result from the local geology but
from a buried gas pipe-line, aligned subparallel to that profile. If s
elf-organized crustal evolution generally produces signatures that can
be described as correlated noise, within a limited bandwidth of spect
ral exponents, erraneous or disturbed data could eventually be discrim
inated from records containing purely natural data by applying analysi
s tools of the dynamic system theory together with autocorrelation tes
ts. Copyright (C) 1996 Elsevier Science Ltd