Mantle Structure Beneath the Western US and its Implications for Convection Processes
Richard M. Allen
University of California, Berkeley
J. Geophys. Res. , 115 B07303, doi:10.1029/2008JB006079, 2010
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We present tomographic images of the mantle structure beneath the western USA. Our Dynamic North America Models of P- and S-velocity structure (DNA07-P and DNA07-S) use teleseismic body-waves recorded at #600 seismic stations provided by the Earthscope Transportable Array and regional networks. DNA07-P and -S benefit from the unprecedented aperture of the network while maintaining a dense station distribution providing high-resolution body-wave imaging of features through the transition zone and into the lower mantle. The main features imaged include (1) the Juan de Fuca subduction system that bottoms at # 400 km beneath Oregon, implying interaction with the Yellowstone anomaly; (2) a low velocity conduit beneath Yellowstone National Park that bottoms at 500 km and dips towards the northwest; (3) shallow low velocity anomalies (upper 200 km) beneath the eastern Snake River Plain (ESRP) and the High Lava Plains, and a deep low velocity anomaly (>600km) beneath the ESRP but not Newberry; (4) a low velocity "slab gap" to # 400 km depth immediately south of the Mendocino Triple Junction and south of the Gorda slab; and (5) high velocity "drips" beneath the Transverse Ranges, the southern Central Valley/Sierra Nevada, and central Nevada. These observations reveal extremely heterogeneous mantle structure for the western USA and suggest we are only just beginning to image the complex interactions between geologic objects. The transportable array allows for analysis of the relationships between these anomalies in an internally consistent single tomographic model.
The DNA07 velocity models are available for download and slicing at http://dna.berkeley.edu.
© Richard M Allen