By using electrotelluric time series, that is, data sets of the electric se
lf-potential variations in a place close to the Middle American Tectonic Tr
ench, we compare two methods of dynamical analysis. First, we calculate the
spectral exponent alpha by means of fast Fourier transforms, and on the ot
her hand we calculate the fractal dimension D of the time series by using t
he so-called Higuchi's algorithm, We find that the second method has remark
able advantages over the spectral analysis.