Tomographic Pn Velocity and Anisotropy Structure in the Central and Eastern United States

Abstract A total of 19,166 Pn phase readings from the International Seismological Centre (ISC) and the National Earthquake Information Center (NEIC) catalogs as well as hand-picked arrivals from the Incorporated Research Institutions for Seismology (IRIS) Data Management Center were inverted to map the velocity and anisotropy structure of the lithospheric mantle in the central and eastern United States (CEUS). Our Pn tomographic model shows a broad region of very fast velocity under the North American craton (the northern CEUS) and significant lateral variations within the rest of the CEUS. The surface locations of the major intraplate seismic zones are near the edges of high-velocity anomalies, which is consistent with the notion that stress accumulation and hence focused deformation are likely to occur at the rheological boundaries around the rigid lithospheric root. However, the ancient rifts show no clear correlation to the low-velocity anomalies in the lithospheric mantle. Our Pn anisotropic model shows a complex pattern of fast directions with an overall north–south trend in the CEUS that may reflect the preserved fabrics of the cratonic lithosphere. Nonetheless, high Pn anisotropy seems to wrap around the high-velocity blocks, which may indicate local deformation around the rigid blocks.