High‐Resolution Tomographic Imaging of the Northern Appalachian Anomaly, New England, US

Abstract

The eastern margin of North America is a passive continental margin, yet it exhibits substantial upper mantle heterogeneity. Beneath New England, upper mantle structure is dominated by the presence of a slow velocity anomaly, the Northern Appalachian Anomaly (NAA), whose origins are not well understood. Here we present a new, high‐resolution teleseismic P‐wave traveltime tomography model of mantle structure beneath the northeastern US and southeastern Canada. We incorporate data from USArray, the Canadian National Seismograph Network, other permanent arrays, and three dense temporary arrays deployed in the NAA region: the New England Seismic Transects (NEST), GEology of New England via Seismic Imaging Studies (GENESIS), and the Seismic Experiment for Imaging Structure beneath Connecticut (SEISConn). The use of data from temporary experiments with dense (5–25 km) station spacing allows us to resolve the NAA with unprecedented detail. The NAA appears clearly in our model, extending from roughly 60–200 km depth, with a maximum amplitude of ∼−4 dVp/Vp. The NAA appears confined to the upper mantle in our models, and does not appear physically connected to slow velocity anomalies in the mantle transition zone. We also image a narrow, nearly columnar feature associated with fast velocities beneath Connecticut, which extends throughout the upper mantle and to the base of the transition zone. Possible explanations for this feature include a fragment that has detached from the continental lithosphere above the NAA or the downwelling limb of an edge‐driven convection cell.