SKS SPLITTING MEASUREMENTS PROBING DEFORMATION AND MANTLE FLOW BENEATH NEW ENGLAND

Beneath New England lies the Northern Appalachian Anomaly (NAA), a roughly ~400-km upper mantle geophysical anomaly, generally observed via seismic tomographic imaging and centered beneath New Hampshire. The NAA, which represents a region of relatively slow upper mantle velocities, is generally co-located with Jurassic to Cretaceous intraplate magmatism post-dating the breakup of Pangea, as well as with unusual topographic uplift and accelerated erosion in the White Mountains of New Hampshire during the Late Cretaceous. Previous work has shown that the NAA coincides with a localized decrease in SKS splitting delay times, which may indicate vertical mantle flow.

Here we present preliminary SKS splitting measurements from stations of the New England Seismic Transects (NEST) and GENESIS (GEology of New England via Seismic Imaging Studies) seismic deployments. NEST is composed of 24 broadband stations deployed in two linear transects across MA (southern line) and VT, NH, and ME (northern line), recording data from 2018-present. The GENESIS array is composed of 6 broadband stations deployed across the Nashoba Terrane in eastern Massachusetts, recording seismic data from 2022-present. Preliminary results reveal some larger SKS splitting delay times (~1 s) in southern New England, with mostly smaller (~0.5 s or less) delay times in Northern New England. Fast directions trend generally nearly E-W, consistent with previous studies, but several individual stations show significant scatter in estimated fast directions, with evidence for clear variations in splitting parameters with backazimuth. Our initial SKS splitting results from NEST and GENESIS are consistent with a model in which upwelling flow in the upper mantle associated with the NAA leads to a nearly vertically oriented fast axis of anisotropy and weak or absent SKS splitting.