9614705 Fischer This research involves a study of the direction of mantle flow around deep continental roots in the northeastern U.S. by means of the mapping of the direction of anisotropy, and a study of the vertical distribution of that anisotropy. Anisotropy measurements will be done through shear-wave splitting from existing SKS and Ps phases converted from upper mantle discontinuities and from a deployment of PASSCAL seismic stations to fill in gaps in coverage. The vertical distribution of anisotropy will be determined from the comparison of splitting of Ps from discontinuities at different depths. A series of 2- and 3-D numerical calculations will model the strain fields and anisotropy produced by strong continents translating through weaker surrounding mantle. The study should allow the assessment of flow patterns around continental roots, the degree of strain produced in continents by present-day plate motion versus fossil deformation, and the degree of coupling between continental roots and the deeper mantle. The flow and coupling are important for the determination of crustal forces that are responsible for earthquakes in the eastern U.S. This research is a component of the National Earthquake Hazard Reduction Program. ***
