SPATIAL VARIATIONS OF TELESEISMIC P-WAVE ATTENUATION AND SCATTERING BENEATH THE SOUTHEASTERN UNITED STATES

We use P-wave amplitude spectra from over 500 teleseismic events recorded by broadband seismic stations in the southeastern United States to examine the spatial variations of seismic attenuation in the crust and upper mantle. Seismic attenuation parameters (∆t*) are obtained by the procedure based on the spectral ratio method using the mean spectrum computed over all the stations as the reference spectrum. The resulting measurements reveal a zone of relatively low attenuation in the Gulf of Mexico Coastal Plain and the southwestern terminus of the Piedmont province. Spatial coherency analysis of the ∆t* observations suggests that the center of the low attenuation layer is located within the uppermost mantle at about 70 km depth. This low attenuation anomaly lies along the suture zone between Laurentia and Gondwana and approximately coincides with the east-west trending Brunswick magnetic anomaly. The origin of this low attenuation anomaly can be attributed to low attenuation bodies in the form of remnant fossil lithospheric fragments in the deep crust or the uppermost mantle. Relative to the rest of the study area, the Coastal Plain demonstrates weaker scattering which is suggestive of a more homogenous crustal and upper-most mantle structure.