Supercontinent cycles are a poorly understood, but paramount, process in shaping Earth's surface. Geologic evidence strongly supports the existence of the supercontinent Pangea 200 million years ago. Alleged earlier supercontinents such as Rodinia (roughly 1 billion years ago) and Columbia (roughly 1.8 billion years ago) suggest that continents do aggregate and disperse in some cyclical fashion. However, there is currently no theoretical basis for the regularity of such cycles. Phillips and Bunge present numerical models of mantle convection with continents in a spherical geometry that show that periodic supercontinent cycles are unlikely to occur if hot plumes rising from the base of the mantle are of sufficient strength. This could have implications for the interpretation of global mountain building episodes, the stability of Earth's rotation axis, flood basalt generation, and even global climate events.
Paleoseismological data suggest the occurrence of four bursts of seismic moment release in the Los Angeles region during the past 12,000 years. The historic period appears to be part of an ongoing lull that has persisted for about the past 1000 years. These periods of rapid seismic displacement in the Los Angeles region have occurred during the lulls between similar bursts of activity observed on the eastern California shear zone in the Mojave Desert, which is now seismically active. A kinematic model in which the faults of the greater San Andreas system
|Contact: Ann Cairns|
Geological Society of America