Tomography, Seismotectonics, and Mantle Dynamics of Central and Eastern United States

Abstract

We study the 3-D P wave velocity structure of the crust and mantle down to 1,000-km depth beneath the central and eastern United States. A 3-D velocity model is obtained by conducting a joint inversion of 236,670 arrival times of local earthquakes and 870,455 relative traveltime residuals of teleseismic events recorded by the EarthScope/USArray Transportable Array. Significant low-velocity (low-V) anomalies are revealed in the crust beneath the eastern arm of the Midcontinent Rift and the Triassic Basins along the East Coast, whereas a prominent high-velocity (high-V) anomaly is visible beneath the Llano Uplift in central Texas. The stable North American Craton exhibits high-V anomalies at depths of 65–250 km. Low-V anomalies exist along the eastern and southern margins of the craton, which may reflect relatively thin lithosphere there. A prominent low-V anomaly is revealed at depths of 50–200 km beneath the New Madrid Seismic Zone, which is bounded by high-V anomalies to its southeast and northwest. This feature reflects a weak lithosphere surrounded by relatively strong cratonic regions and stress concentration caused intraplate seismicity in the New Madrid region. Two high-V bodies appear in the mantle transition zone (410- to 660-km depths) beneath the Interior Low Plateaus, the central Great Plains, and the Central Lowland, which may reflect the subducted Farallon plate or delaminated lithosphere. At depths of 800–1,000 km, a high-V anomaly is visible beneath the southeast United States, which may be the subducted Hess Rise conjugate.