Crustal and Mantle Anisotropy of the Hoggar Swell, Northwest Africa
Abstract
The Hoggar swell of Algeria is one of the several topographic highs and Cenozoic basaltic volcanic centers in Northwest Africa. The formation mechanism of the high elevation and volcanism remains enigmatic, partly because of limited knowledge regarding the crustal and mantle structure due to lack of sufficient coverage by seismic stations in the area. In this study, we apply several structural seismological techniques to analyze broadband seismic data recorded by GEOSCOPE Station TAM over an ~30 year period to systematically investigate seismic azimuthal anisotropy in the crust, the upper mantle, the mantle transition zone, and in the lower mantle, using XKS splitting and systematic azimuthal moveout of P-to-S converted phases from the Moho and the 410 and 660 km discontinuities. Preliminary results indicate that the mean fast orientation from 270 XKS measurements is nearly N-S, and the mean splitting time is 1.0 s. The splitting parameters from events in the NE quadrant, which are mostly SKKS events, show a clear azimuthal variation with a 90-degree periodicity, probably suggesting multiple-layered anisotropy in the area to the NE of the station. Splitting parameters from SKS and SKKS from the same events are almost identical to each other, which suggest that the observed anisotropy is dominantly from the upper mantle. While the fast orientation of crustal anisotropy revealed by the azimuthal moveout of the Pms phase is within 10 degrees from the XKS fast orientation, the crustal splitting time is about 0.25 s which is significantly smaller than the XKS splitting time. Results from anisotropy analysis using P-to-S conversions from the 410 and 660 km discontinuities and their tectonic implications will be discussed. This study demonstrates the effectiveness of applying multiple structural seismological techniques to data from long-running seismic stations in delineating the crustal and mantle structure and anisotropy.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMS061.0009L
- Keywords:
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- 7299 General or miscellaneous;
- SEISMOLOGY