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Abstract Seismic wave amplitudes have tremendous sensitivity to subduction structure; however, they are affected by attenuation, scattering and focusing, and have therefore been sparsely used compared with traveltimes. We measure and model teleseismic body wave amplitudes recorded at a dense broadband array in the Washington Cascades. These data show anomalous amplitude variations with complex azimuthal dependence at frequencies as low as 0.05 Hz, accompanied by significant multipathing. We demonstrate using spectral‐element numerical simulations that focusing of the teleseismic wavefield by the Juan de Fuca slab is responsible for some of the amplitude anomalies. The focusing effects can contaminate the apparent differential attenuation measurements and produce at least 20% of the inferred attenuation signal. Our results indicate that the amplitudes are sensitive to the subducting slab geometry and subduction structure, and can be used to refine seismic images. Ubiquitous and consistent amplitude anomalies are observed along the arc, suggesting that the Juan de Fuca slab may be continuous from Canada to northern California.
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Mantle dynamics beneath the discrete and diffuse plate boundaries of the Juan de Fuca plate: Results from Cascadia Initiative body wave tomography: TOMOGRAPHIC IMAGING WITH CASCADIA INITIATIVE DATA
- PAR ID:
- 10042085
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geochemistry, Geophysics, Geosystems
- Volume:
- 18
- Issue:
- 8
- ISSN:
- 1525-2027
- Page Range / eLocation ID:
- 2906 to 2929
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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