  Anomalous temporal fluctuations of helium concentrations in spring emanations
have been observed on a number of occasions prior to some major seismic events.
Several recent studies have shown that a wide variety of natural systems
display significant fluctuations that may be characterized by long-range
power-law correlations. We have applied detrended fluctuation analysis (DFA) to
characterize preseismic helium anomalies and to probe the relationship between
two classes of apparently irregular helium sequences. Application of the DFA
technique reveals a crossover phenomenon that distinguishes short-range from
long-range scaling exponents; the crossover corresponds to a transition from
nonpersistent to persistent traits in the helium time series. Our findings
imply a significant statistical correlation between anomalous helium
concentration and a fluctuation exponent. This analytical approach appears to
be a promising way for identifying anomalous helium fluctuations as signals
precursory to an earthquake.
