Frequency Dependent quasi-Love Wave Scattering Along the Eastern North American Margin
Abstract
The passive Eastern North American Margin (ENAM) is characterized by a sharp change in anisotropy crossing the coastline. Shear wave splitting measurements recorded offshore on broadband ocean bottom seismometers have shown strong margin parallel path integrated anisotropy. Onshore, this transitions to null splits at stations on the coastal piedmont. The offshore splitting was originally interpreted as resulting from asthenospheric flow fabrics, but a recent active source study showing fast margin-parallel Pn phases suggests a lithospheric provenance. The offshore extent of any such intra-plate fabric is unknown, as is the precise nature of an anisotropic gradient at the ocean-continent transition. We harness observations of Love-to-Rayleigh wave scattering to locate sharp lateral gradients in anisotropy at ENAM. When a Love wave encounters an abrupt lateral anisotropic gradient, Love wave energy is scattered to Rayleigh waves through normal mode coupling, with the scattered phase termed a "quasi-Love" wave. Long period quasi-Love waves have been previously observed along the ENAM, but do not have the depth sensitivity to place constraints on a lithospheric or asthenospheric source of anisotropy. We examine quasi-Love scattering along the ENAM at a variety of frequency bands to gain insights into the depth distribution of anisotropic gradients. We find strong scattering across the margin at longer periods consistent with previous results. At shorter periods (50-60 seconds), much of the quasi-Love scattering along ENAM disappears suggesting a deeper, likely asthenospheric, source for the anisotropic gradient.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMT007...05L
- Keywords:
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- 7209 Earthquake dynamics;
- SEISMOLOGY;
- 7280 Volcano seismology;
- SEISMOLOGY;
- 8105 Continental margins: divergent;
- TECTONOPHYSICS;
- 8413 Subduction zone processes;
- VOLCANOLOGY