Detrended fluctuation analysis of the magnetic and electric field variations that precede rupture

Magnetic field variations are detected before rupture in the form of `spikes' of alternating sign. The distinction of these `spikes' from random noise is of major practical importance, since it is easier to conduct magnetic field measurements than electric field ones. Applying detrended fluctuation analysis (DFA), these `spikes' look to be random at short time-lags. On the other hand, long range correlations prevail at time-lags larger than the average time interval between consecutive `spikes' with a scaling exponent $\alpha$ around 0.9. In addition, DFA is applied to recent preseismic electric field variations of long duration (several hours to a couple of days) and reveals a scale invariant feature with an exponent $\alpha \approx 1$ over all scales available (around five orders of magnitude).