Determining what lies beneath Earth's surface requires sophisticated technology. Ed Garnero, a professor in the School of Earth and Space Exploration in the College of Liberal Arts and Sciences, and seismology graduate student Chunpeng Zhao use seismic wave data from the USArray Transportable Array to construct a picture of the deep earth. The fall 2009 issue of onSite, the newsletter of the earth science program EarthScope, featured the research of Garnero and Zhao on the front page in the article, "Heterogeneous Lowermost Mantle Beneath the Pacific Ocean."

The seismic stations of the Transportable Array (TA) record earthquakes from around the globe. As seismic waves travel through the Earth, they are affected by the structure and composition they pass through. Scientists are then able to deduce Earth's structure between source and station. The dynamics and evolution of the deep interior are likely closely linked to Earth's outermost shell(s), including tectonic plates, their motions and evolution, making seismic imaging of deep Earth structure very important.

"To understand processes associated with low velocity provinces, it is important to constrain elastic property contrast across edges because strong lower mantle activities, e.g. partial melting, mineral phase transition or mantle flow, are usually associated with edges of these low velocity provinces," explains Chunpeng.

A more complete and better understanding of the area beneath the Pacific Ocean has long been a priority for seismologists since it is such a hotbed of activity. The TA is situated to record waves that originate from Fiji-Tonga, the spot from which the largest number of deep-focus earthquakes originates. Earlier studies had established the presence of a large low shear velocity province in the region below the Central Pacific. Garnero and Zhao have been able to add to this image, most notably by suggesting that the area is of a chemically distinct origin and mapping the northern edge of the low-velocity material.

According to Garnero, "Mapping out the details of these low velocities provinces, especially their edges, is a prerequisite for inferring deep mantle flow patterns responsible for sweeping the material into a pile in the first place. If we can learn more about deep mantle flow (and hence mantle convection in general), then there is hope that we might be able to better unravel the evolution of the interior, and hence planet as a whole."

For more information on EarthScope, or to read the fall 2009 newsletter, please visit: http://www.earthscope.org/

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