EarthScope - of slabs, drips, and plumes
Friday, 2. October 2009, 09:10:38
The USArray network of seismometers is revealing an impressive subsurface collection of slabs, drips, and plumes across the U.S. USArray is part of the EarthScope experiment, a 15-year program to place a dense network of permanent and portable seismographs across the continental United States. By analyzing the records of earthquakes obtained from this dense grid of seismometers, scientists can learn about Earth structure and dynamics and the physical processes controlling earthquakes and volcanoes. You can follow the work through the EarthScope quarterly newsletter (onSite) all free downloadable in pdf-format from here.
The work is most recently featured in an article by Richard A. Kerr in the 25 September 2009 issue of the journal Science.
Mantle plume:
Transportable Array data add to evidence of a seismically slow zone beneath Yellowstone extending to a depth of at least 1000 kilometres (that means down into the lower mantle). Some scientists see this as evidence that a mantle plume exists to lower mantle depth. Is there a single tall plume or a random series of unconnected blobs beneath Yellowstone?
Lithospheric drip (also called “Mantle Drip”):
Combined data from the Flexible Array and the Transportable Array as the latter was passing over the Isabella Anomaly (a blob of rock lying 70 km to 250 km beneath the western edge of the Sierra Nevada mountains of central California). A density was calculated for the anomaly’s rock, which shows that it is so dense that it must contain just the kind of rock hypothesized to have dripped away from the base of the Sierra Nevada. It was concluded that the drip could have triggered the Sierra Nevada’s uplift. (See my post on Litospheric Drip).
And there are more strange features still to be further explored. Indeed relating geological traces at the surface to underlying seismic anomalies could help explain why there’s such a weird assortment of still-active deep processes shaping the surface of the American West.
The Fall 09 issue of the EarthScope onSite newsletter features the Heterogeneous Lowermost Mantle Beneath the Pacific Ocean and Tectonic Block Motions in Southeast Alaska and Adjacent Canada.
The work is most recently featured in an article by Richard A. Kerr in the 25 September 2009 issue of the journal Science.
Mantle plume:
Transportable Array data add to evidence of a seismically slow zone beneath Yellowstone extending to a depth of at least 1000 kilometres (that means down into the lower mantle). Some scientists see this as evidence that a mantle plume exists to lower mantle depth. Is there a single tall plume or a random series of unconnected blobs beneath Yellowstone?
Lithospheric drip (also called “Mantle Drip”):
Combined data from the Flexible Array and the Transportable Array as the latter was passing over the Isabella Anomaly (a blob of rock lying 70 km to 250 km beneath the western edge of the Sierra Nevada mountains of central California). A density was calculated for the anomaly’s rock, which shows that it is so dense that it must contain just the kind of rock hypothesized to have dripped away from the base of the Sierra Nevada. It was concluded that the drip could have triggered the Sierra Nevada’s uplift. (See my post on Litospheric Drip).
And there are more strange features still to be further explored. Indeed relating geological traces at the surface to underlying seismic anomalies could help explain why there’s such a weird assortment of still-active deep processes shaping the surface of the American West.
The Fall 09 issue of the EarthScope onSite newsletter features the Heterogeneous Lowermost Mantle Beneath the Pacific Ocean and Tectonic Block Motions in Southeast Alaska and Adjacent Canada.
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http://www.sciencemag.org/cgi/content/summary/325/5948/1620-a
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http://www.earthscope.org/
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http://www.iris.edu/USArray/
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