16-52 Investigating Upper Mantle Seismic Anisotropy in the Northern Appalachian Anomaly Region, New England, USA, via SKS Waveform Analysis

Session: From Thin Section to Outcrop: Exploration of Undergraduate Research (Posters)

Presenting Author:

Authors:

Abstract:

The Northern Appalachian Anomaly (NAA) is a region of unusually slow, and thus presumably hot, upper mantle beneath much of the New England Appalachians. While hot upper mantle material would presumably be less dense than the surrounding mantle, and thus positively buoyant, the pattern of mantle flow associated with the NAA remains poorly understood. Previous work by Levin et al. (2018) and Espinal (2025) have suggested that there may be a localized reduction in shear wave splitting delay times, with more null SKS arrivals, in the region. Shear wave splitting is an indicator of mantle anisotropy; in the case of predominantly vertical mantle flow, one would expect a vertically aligned fast axis of anisotropy, which would in turn produce weak splitting with small delay times. An observation of small shear wave splitting delay times would thus be consistent with vertical mantle flow.

In this study, we use broadband seismic data from the NAA region (spanning 71-73°W and 41-47°N), including data from dense temporary arrays recently deployed in the area (the NEST, GENESIS, and SEISConn experiments). We evaluate the hypothesis of weak or absent splitting in the NAA region by the analysis of SKS waveforms. Specifically, we inspect the amplitudes of transverse component waveforms for individual SKS arrivals measured at stations in the NAA region, since smaller transverse component amplitudes correspond to generally weaker splitting. We examine SKS waveforms from teleseismic earthquake arriving from a range of directions. We find evidence for smaller transverse component amplitudes near the center of the NAA (near ~44°N latitude)  for several earthquakes, supporting the idea of weak shear wave splitting due to upper mantle anisotropy associated with the NAA. We investigated the data at a range of frequencies, allowing us to probe sensitivity to structure on various length and depth scales. Our observations support, although do not uniquely constrain, a possible role for vertical mantle flow in explaining upper mantle seismic anisotropy in the NAA region.

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.