Detailed, upper mantle P and S wave velocity (Vp and Vs) models are developed for the northern Mississippi Embayment (ME), a major physiographic feature in the Central United States (U.S.) and the location of the active New Madrid Seismic Zone (NMSZ). This study incorporates local earthquake and teleseismic data from the New Madrid Seismic Network, the Earthscope Transportable Array, and the FlexArray Northern Embayment Lithospheric Experiment stations. The Vp and Vs solutions contain anomalies with similar magnitudes and spatial distributions. High velocities are present in the lower crust beneath the NMSZ. A pronounced low‐velocity anomaly of ~ −3%–−5% is imaged at depths of 100–250 km. High‐velocity anomalies of ~ +3%–+4% are observed at depths of 80–160 km and are located along the sides and top of the low‐velocity anomaly. The low‐velocity anomaly is attributed to the presence of hot fluids upwelling from a flat slab segment stalled in the transition zone below the Central U.S.; the thinned and weakened ME lithosphere, still at slightly higher temperatures from the passage of the Bermuda hotspot in mid‐Cretaceous, provides an optimal pathway for the ascent of the fluids. The observed high‐velocity anomalies are attributed to the presence of mafic rocks emplaced beneath the ME during initial rifting in the early Paleozoic and to remnants of the depleted, lower portion of the lithosphere.

Shear wave splitting associated with the Mississippi Embayment (ME) is determined using teleseismic SKS phases recorded by the Northern Embayment Lithosphere Experiment (NELE), the USArray Transportable Array (TA), and the New Madrid seismic network for the period 2005–2016. Our data set consists of ~5900 individual splitting measurements from 257 earthquakes recorded at 151 stations within and outside the ME. Stations outside of the ME exhibit significant shear wave splitting, with average delay times between ~ 0.4 s and ~1.8 s. To the northeast and east of the ME, nearly all observed fast orientations are approximately oriented northeast‐southwest, in agreement with absolute plate motion (APM) predicted by HS3‐Nuvel‐1A. The homogeneity of the fast orientations in this region suggests that the splitting is due to active flow in the asthenosphere. A counterclockwise rotation in the splitting orientation is observed moving northeast to northwest across the study area. Inside the ME, some stations show large and systematic deviations of the measured fast orientations from the APM. The delay times within the entire ME range from ~0.9 s to ~ 2.1 s. Splitting complexity is attributed to relic lithospheric fabrics formed during past tectonic events including passage of a hot spot in mid‐Cretaceous time. The anisotropy may also be linked to the presence of a southwest dipping region of low P and S wave velocities below the ME or to deeper flow in the asthenosphere.

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