The velocity structure and anisotropy of the central and southern Atlantic lithosphere from surface wave studies
Abstract
Beneath the south east Atlantic Ocean previous tomographic work shows that velocities at depths greater than 100km are faster than those predicted using simple velocity - temperature conversions and the widely accepted plate model. Furthermore, at these depths, variations in velocity continue to show a correlation with age. Here, we present preliminary results from two surface wave techniques, to investigate in detail the structure and dynamics of the upper mantle under the central and southern Atlantic Ocean. Group velocity dispersion curves for oceanic paths have been obtained using the Multi Filter Technique for approximately 10,000 paths between periods of 20s and 100s. The path-average group velocities are then combined within a tomographic inversion, to obtain the regional variations in velocity. These short to intermediate period group velocities have depth sensitivities from the surface to approximately 90km, constraining the focus to velocity variations within the lithosphere rather than the whole lithosphere-asthenosphere system. There is a clear distinction at all periods between oceanic and continental velocities. Velocity variations beneath the ocean define key features such as a region of low velocity beneath the ridge at all periods, most strongly picked out in the south of the region. In the south east, where there is the most optimal path coverage, we see a correlation between the age of lithosphere and increase in velocity at longer periods. Following the group velocity analysis, the same data have been inverted for shear velocity structure using a waveform inversion technique. Path-average shear velocity is computed for each data and again incorporated into a tomographic inversion. Periods from 50-160s are included in the waveform inversion, thus giving a focus on the deeper lithospheric structure and variations at the lithosphere-asthenosphere boundary. Additionally, we present results which incorporate azimuthal anisotropy in the tomographic inversions. From comparisons of the anisotropic results at a variety of periods and depths, we provide further information on the link between dynamic flow within the asthenosphere, and deformation of the overlying plate.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.T33G2733M
- Keywords:
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- 7270 SEISMOLOGY / Tomography;
- 8120 TECTONOPHYSICS / Dynamics of lithosphere and mantle: general