Abstract
The nature of the long-run correlations in a seismic catalog (the Iberian Peninsula catalog recorded from 1970 to 2001) is analyzed by means of the Hurst exponent. Different techniques, tested with simulated time series, are used to calculate this parameter, so that the results are reliable. We find that there is strong correlation in the region, and that small earthquakes are very important to the stress transfers. In addition, it is shown that predictability in an earthquake system is a function of the relationship between magnitude and energy, and that seismicity rate, or number of events, provides the best measure of this predictability.