Seismic surveys of the Juan de Fuca tectonic plate, located off the northwest coast of the USA, have revealed that a giant magma chamber may be helping to reduce the rate and magnitude of earthquakes in the region.
 
Geologists from the University of California, Berkeley, have proposed that a large area of upwelling hot rock has effectively lubricated the movement at the plate’s boundary as it subducts under the vast North American plate. This, they believe, has reduced the build-up of stress that often occurs along such zones and is released in the form of earthquakes when the plates suddenly slip and adjust to their new positions.

When Professor Richard Allen and colleagues used seismographic data to build a three-dimensional model of the Juan de Fuca plate, they discovered an unusually
warm area at depths below 400 kilometres, where a 180-kilometre-thick slab of the plate should be. They speculate that this area is left over from a time when a mantle plume known as the Yellowstone plume was located in the region. The actual Yellowstone plume has since migrated east, below Wyoming, where it fuels the largest and potentially most dangerous volcanic system in North America, the Yellowstone supervolcano.

January 2008