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3-D model shows big body of water in Earth's mantle
One of the most dramatic features in the Wysession et. al global mantle shear-wave attenuation model is a very high-attenuation anomaly at the top of the lower mantle beneath eastern Asia. This anomaly is believed due to water that has been pumped into the lower mantle via the long history of the subduction of oceanic lithosphere — crust and upper mantle — in this region. The left figure is a slice through the earth, showing the attenuation anomalies within the mantle. The location of the slice — red line in the upper right figure — is a map of the seismic attenuation at a depth of roughly 620 miles. In both images, red shows unusually soft and weak rock, and blue shows unusually stiff rock (yellow and white show near-average values). The two figures in the lower right are resolution tests to see if the data have the resolution to retrieve Earth structure in these parts of the Earth. The sharper the black-white transitions are, the better the resolution is. Credit: Washington University in St. Louis
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A seismologist at Washington University in St. Louis has made the first 3-D model of seismic wave damping — diminishing — deep in the Earth's mantle and has revealed the existence of an underground water reservoir at least the volume of the Arctic Ocean. It is the first evidence for water existing in the Earth's deep mantle.
Michael E. Wysession, Ph.D., Washington University professor of earth and planetary sciences in Arts & Sciences, working with former graduate student Jesse Lawrence (now at the University of California, San Diego), analyzed 80,000 shear waves from more than 600,000 seismograms and found a large area in Earth's lower mantle beneath eastern Asia where water is damping out, or attenuating, seismic waves from earthquakes.
The traditional method seismologists use to image the Earth below us is to measure the speed of seismic waves. This will provide a sort of CAT scan of the Earth's core and mantle. Using wave speeds alone is a problem, however, because they cannot distinguish between temperature and composition variations.
The research is described in a forthcoming monograph, Earth's Deep Water Cycle, which is in press to be published by the American Geophysical Union.
>
3-D model shows big body of water in Earth's mantle
One of the most dramatic features in the Wysession et. al global mantle shear-wave attenuation model is a very high-attenuation anomaly at the top of the lower mantle beneath eastern Asia. This anomaly is believed due to water that has been pumped into the lower mantle via the long history of the subduction of oceanic lithosphere — crust and upper mantle — in this region. The left figure is a slice through the earth, showing the attenuation anomalies within the mantle. The location of the slice — red line in the upper right figure — is a map of the seismic attenuation at a depth of roughly 620 miles. In both images, red shows unusually soft and weak rock, and blue shows unusually stiff rock (yellow and white show near-average values). The two figures in the lower right are resolution tests to see if the data have the resolution to retrieve Earth structure in these parts of the Earth. The sharper the black-white transitions are, the better the resolution is. Credit: Washington University in St. Louis
>
A seismologist at Washington University in St. Louis has made the first 3-D model of seismic wave damping — diminishing — deep in the Earth's mantle and has revealed the existence of an underground water reservoir at least the volume of the Arctic Ocean. It is the first evidence for water existing in the Earth's deep mantle.
Michael E. Wysession, Ph.D., Washington University professor of earth and planetary sciences in Arts & Sciences, working with former graduate student Jesse Lawrence (now at the University of California, San Diego), analyzed 80,000 shear waves from more than 600,000 seismograms and found a large area in Earth's lower mantle beneath eastern Asia where water is damping out, or attenuating, seismic waves from earthquakes.
The traditional method seismologists use to image the Earth below us is to measure the speed of seismic waves. This will provide a sort of CAT scan of the Earth's core and mantle. Using wave speeds alone is a problem, however, because they cannot distinguish between temperature and composition variations.
The research is described in a forthcoming monograph, Earth's Deep Water Cycle, which is in press to be published by the American Geophysical Union.
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