Seismic Images of the North American Upper Mantle From S-to-P Converted Waves

Date: 4/26/2019

Time: 10:45 AM

Room: Vashon

We present new seismic images of the key structural elements of the upper mantle beneath the continuous USA and southern Canada. Our method is based on the well-established S-to-P seismic converted wave technique, but with the important difference that we do not used seismic deconvolution, as is conventionally done. We avoid deconvolution because this processing step can introduce strong artifacts into the resultant seismic images. We present comparisons of our preferred plain stacking method versus deconvolution methods. Our imaging results are significantly different from previous studies that use deconvolution. We image the lithosphere-asthenosphere boundary (LAB), but without a mid-lithospheric discontinuity (MLD). This suggests that the MLD may be an artifact introduced by seismic deconvolution. Other prominent features are the Lehmann discontinuity and the 410-discontinuity with a low velocity layer above it. Two newly-discovered features in our seismic images are: (1) a northwest dipping boundary in the uppermost mantle beneath the Archean Superior craton that we interpret as early Proterozoic subducted oceanic lithosphere, and (2) a southeast dipping boundary just below the Moho beneath eastern Texas that we interpret as the Paleozoic suture between Laurentia and Gondwana, marking the formation of Pangea.

Presenting Author: Walter D. Mooney

Authors