Imaging the seismic velocity structure of the crust and upper mantle in the northern East African Rift using Rayleigh wave tomography

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Authors

Emma Louise Chambers , Nicholas Harmon , Catherine Rychert , Ryan Gallacher, Derek Keir 

Abstract

Within the northern East African Rift, multiple seismic models have been produced to understand the evolution of magmatism, however variations in method, resolution, and scale make direct comparisons challenging. The lack of instrumentation off rift further limits our understanding of the spatial extent of tectonic and magmatic processes, which is crucial to understanding magmatic continental rifting. In this paper, we jointly invert Rayleigh wave dispersion curves from ambient noise and teleseisms to obtain absolute shear velocity maps at 10–150 km depth. This includes data from a new seismic network located on the Ethiopian Plateau and enhanced resolution at Moho and upper mantle depths from the joint inversion. At crustal depths, velocities are slowest beneath the Main Ethiopian Rift and the off rift Ethiopian Plateau (<3.00-3.75 ±0.04 km/s, 10–40 km depth), which are slow enough to require ongoing magmatic emplacement. At 60–80 km depth off rift, we observe a fast velocity lid (>0.1 km/s faster than surroundings), which corresponds to previous estimates of the lithosphere-asthenosphere-boundary. The fast lid is not observed within the rift in locations underlain by asthenospheric slow velocity anomalies (<4.05 ±0.04 km/s at 60–120 km depth), suggesting melt is infiltrating the lithosphere within the rift. Furthermore, the asthenospheric slow velocity anomalies are segmented (~110x80 km wide), existing in areas that have not undergone significant crustal and plate thinning, suggesting segmented melt supply starts prior to significant plate deformation. Finally, the segmented asthenospheric slow velocity zones are not directly located beneath melt-rich crustal regions, particularly for those off rift, suggesting mantle melt either migrates laterally during ascent, and/or that melt is ephemeral.

DOI

https://doi.org/10.31223/X5XK6X

Subjects

Geophysics and Seismology

Keywords

Seismology, East African Rift

Dates

Published: 2021-04-13 20:43

License

CC BY Attribution 4.0 International

Additional Metadata

Data Availability (Reason not available):
The data is not currently available as we are releasing the final model if the manuscript is accepted for publication. We have a stored version of the dataset at Our final shear velocity model is available at https://doi.org/10.5258/SOTON/D1408 which will go live on acceptance. For the peer-reviewed version we have provided a Google Drive link so reviewers can view the final model.

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