SPATIOTEMPORAL PATTERNS IN THE ENERGY-RELEASE OF GREAT EARTHQUAKES

For the past 80 years, the energy released in great strike-slip and th rust earthquakes has occurred in alternating cycles of 20 to 30 years. This pattern suggests that a global transfer mechanism from poloidal to toroidal components of tectonic plate motions is operating on time scales of several decades. The increase in seismic activity in Califor nia in recent years may be related to an acceleration of global strike -slip moment release, as regions of shear deformation mature after bei ng reached by stresses that have propagated away from regions of great subduction decoupling earthquakes in the 1960s.