First-Order Characteristics of Mantle Fabrics Revealed by Teleseismic Shear-Wave Splitting Parameters at Broadband Seismic Stations in North America
As a result of the ongoing EarthScope project and advancement in data analysis techniques, there has been a renewed interest to map spatial variation of seismic anisotropy beneath North America over the past several years. We are in the process of finalizing a large data base of shear-wave splitting parameters by re-analyzing all available broadband seismic data recorded by permanent and portable stations, archived at the IRIS Data Management Center. Results to date have revealed several first-order characteristics on the strength and direction of mantle fabrics. These include 1). There is a dramatic gradual eastward decrease in splitting times from the western coast to the Rocky Mountain front, from about 1.5 s to about 1 s which is the global averaged splitting time for continents. The observed splitting times are spatially consistent with a mean value of about 0.9 s in the stable interior of the NA craton. The splitting times at most of the stations in the vicinity of the Appalachians are larger than those in the stable interior but smaller than those in the western US. 2). In the stable interior, the observed fast directions are mostly consistent with the absolute plate motion direction calculated based on the HS3-NUVEL1A model, while there is a significant difference between the two at most of the stations in the western US orogenic zone and in eastern US. 3). Clear azimuthal dependence of splitting parameters is observed at a significant portion of stations on the Colorado Plateau and in the vicinity of the New Madrid Seismic Zone, suggesting the existence of complex anisotropy. 4). Fast directions in Nevada, California and southern Oregon form a nearly semi-circular feature that is consistent with previous studies and can be explained by the NA plate moving on top of an upwelling mantle flow field. Those first-order characteristics suggest that observed seismic anisotropy is the consequence of the combined effect between asthenospheric flow in the direction of APM, small-scale mantle flow associated with plate subduction and mantle upwelling, as well as fossil lithospheric fabrics originated from past orogenic events.
K. H. Liu and S. S. Gao, "First-Order Characteristics of Mantle Fabrics Revealed by Teleseismic Shear-Wave Splitting Parameters at Broadband Seismic Stations in North America," AGU Joint Assembly, American Geophysical Union (AGU), May 2008.
AGU Joint Assembly (2008: May 27-30, Fort Lauderdale, FL)
Geosciences and Geological and Petroleum Engineering
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© 2008 American Geophysical Union (AGU), All rights reserved.
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