Stratified seismic anisotropy and the lithosphereasthenosphere boundary beneath eastern North America

摘要

Long records of teleseismic observations accumulated at permanent seismic stations Harvard, MA; Palisades, NY; and Standing Stone, PA, in eastern North America are inverted for vertical distribution of anisotropic parameters. High-resolution anisotropy-aware P wave receiver function analysis and multiple-layer core-refracted SKS waveform modeling favor more than one layer of anisotropy beneath all sites. Our analyses suggest that the depth sensitivity to stratified anisotropic seismic velocity in converted phases and the SKS waveforms are complementary and confirm that these two approaches yield consistent lithospheric anisotropic fast axis directions.We illustrate the feasibility of the lithosphere-asthenosphere boundary detection on a regional scale through anisotropy-aware receiver functions. Joint interpretation of receiver functions and SKS waveforms beneath eastern North America suggests a thin (~100 km) anisotropic lithosphere with fast axis orientation nearly orthogonal to the strike of major tectonic units and an underlying anisotropic asthenosphere with fast axis directions that favor the HS3-NUVEL 1A plate motion model. Consistent lithospheric anisotropy inferred from both techniques suggests broad presence of coherent fabric in the lower lithosphere, possibly developed in a regional scale delamination event after the assembly of Appalachians.