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

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1093/gji/ggac156. This is version 2 of this Preprint.

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Authors

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

Abstract

Understanding the dynamics and evolution of continental rifting is broadly important for our understanding of plate tectonics. The northern East African Rift offers an excellent opportunity to study these processes at an active rift that was initiated by a large magmatic event. Multiple seismic models have been produced to understand the evolution of magmatism which image punctuated slow velocity zones in the asthenosphere. However, the depth extent of the slow velocity bodies has been less well constrained leading to much debate regarding the primary controls on melt generation. Variations between methods, resolution, and scale of the seismic models make direct quantitative 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) and ongoing magmatic emplacement is required. At 60–80 km depth off-rift, we observe a fast velocity lid (>0.1 km/s faster than surroundings), in agreement with previous estimates of lithospheric thickness from receiver functions. The fast lid is not observed within the Main Ethiopian Rift or central Afar which instead are underlain by asthenospheric slow velocity anomalies (<4.05 ±0.04 km/s at 60–120 km depth). This suggests melt is infiltrating the lithosphere within the rift. Furthermore, punctuated asthenospheric slow velocity anomalies (∼110×80 km wide) exist in areas that have not undergone significant crustal and plate thinning, potentially indicating melt infiltration may start prior to significant plate deformation. Finally, the punctuated asthenospheric slow velocity zones are not located directly beneath melt-rich crustal regions including those off-rift, suggesting melt migration processes are dynamic and/or may occur laterally.

DOI

https://doi.org/10.31223/X5XK6X

Subjects

Geophysics and Seismology

Keywords

Seismology, East African Rift

Dates

Published: 2021-04-14 04:43

Last Updated: 2022-04-28 03:40

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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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