Self-driven mode switching of earthquake activity on a fault system

Theoretical results based on two different modeling approaches indicate tha t the seismic response of a fault system to steady tectonic loading can exh ibit persisting fluctuations in the form of self-driven switching of the re sponse back and forth between two distinct modes of activity. The first mod e is associated with clusters of intense seismic activity including the lar gest possible earthquakes in the system and frequency-size event statistics compatible with the characteristic earthquake distribution. The second mod e is characterized by relatively low moment release consisting only of smal l and intermediate size earthquakes and frequency-size event statistics fol lowing a truncated power law. The average duration of each activity mode sc ales with the time interval of a large earthquake cycle in the system. The results are compatible with various long geologic, paleoseismic, and histor ical records. The mode switching phenomenon may also exist in responses of other systems with many degrees of freedom and nonlinear dynamics. (C) 1999 Elsevier Science B.V. All rights reserved.