Model Update December 2008: Upper Mantle Heterogeneity beneath North America from P-wave Travel Time Tomography with Global and USArray Transportable Array Data

Online material: MIT P -wave tomography model for the United States created using travel-time residuals from the USArray Transportable Array from April 2004 to December 2008. As the Transportable Array of USArray (http://www.iris.edu/USArray/), the seismology component of EarthScope (http://www.earthscope.org/), progresses eastward across the United States, the seismological database available for studies of mantle heterogeneity beneath the North American continent is rapidly expanding. Burdick et al. (2008) published a tomographic model of mantle heterogeneity beneath North America based on USArrayTA P -wave travel time data through November 2007. The purpose of this article is to announce the availability (as an electronic supplement through the SSA Web site. www.seismosoc.org) of model MITP\_USA\_2008DEC, which is based on USArrayTA data through December 2008. By the end of 2008 USArrayTA had begun to illuminate mantle structure below the center of the continent, where systematic high-resolution tomography was previously unavailable. Specifically, data from stations east of the Rocky Mountains provides new constraints on the heterogeneity of the stable North American craton and allows for direct comparison with mantle heterogeneity beneath the tectonically active western margin. Compared to the previous version (Burdick et al. 2008), the current model update refines estimates of mantle heterogeneity around the Yellowstone hotspot, better defining its boundaries and revealing a strong slow anomaly beneath the transition zone. Large-scale structural features in the west, such as the Basin and Range and the Cascadia subduction zone, where data coverage was already good, remain similar to those in the original model, which suggests that the tomographic images of them are now robust. Our tomographic inversions of USArray data are based on the method developed by Karason (2002) and described by Li et al. (2008). We perform global inversions in order to account properly for mantle heterogeneity outside the study area and use an adaptable grid …