Abstract: This article applies random function theory, and uses seismic energy released as the basic elements of seismic activity. Using natural orthogonal function (or empirical orthogonal function) expansion method we discussed the short-term time-space anomaly in the energy field of regional seismic activity before the 2008 Wenchuan 8.0 earthquake. The results show that the time weighting factor of eigenvectors (typical field) corresponding to several major features of the field values shows a prominent long-term abnormal change around the source region before the M8.0 earthquake. The time weighting factor corresponding to everal regional characteristic values of energy field along the Longmenshan fault zone shows very obvious short-term anomaly. The authors believe that this method is worthy of further study for prediction of earthquake activity.

Key words: Energy field, Natural orthogonal function, Typical field, Wenchuan M8.0 earthquake