The University of Southampton
University of Southampton Institutional Repository

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

Imaging the seismic velocity structure of the crust and upper mantle in the northern East African Rift using Rayleigh wave tomography
Imaging the seismic velocity structure of the crust and upper mantle in the northern East African Rift using Rayleigh wave tomography
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.
Africa, Joint inversion, Seismic tomography, Surface waves and free oscillations
0956-540X
2036-2055
Chambers, Emma L.
4226fbb2-4651-4be8-af34-030930bc52d2
Harmon, Nick
783b3238-b228-403c-a67c-92d4b19428ae
Rychert, Kate
0029e134-bb8b-42ca-9946-9ebf62956946
Gallacher, Ryan J.
3d4aa45c-babe-4164-bee2-fc49afda41a7
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Chambers, Emma L.
4226fbb2-4651-4be8-af34-030930bc52d2
Harmon, Nick
783b3238-b228-403c-a67c-92d4b19428ae
Rychert, Kate
0029e134-bb8b-42ca-9946-9ebf62956946
Gallacher, Ryan J.
3d4aa45c-babe-4164-bee2-fc49afda41a7
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65

Chambers, Emma L., Harmon, Nick, Rychert, Kate, Gallacher, Ryan J. and Keir, Derek (2022) Imaging the seismic velocity structure of the crust and upper mantle in the northern East African Rift using Rayleigh wave tomography. Geophysical Journal International, 230 (3), 2036-2055, [ggac156]. (doi:10.1093/gji/ggac156).

Record type: Article

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.

Text
ggac156_unformatted - Accepted Manuscript
Download (3MB)

More information

e-pub ahead of print date: 22 April 2022
Published date: 1 September 2022
Additional Information: Publisher Copyright: © 2022 The Author(s) 2022. Published by Oxford University Press on behalf of The Royal Astronomical Society.
Keywords: Africa, Joint inversion, Seismic tomography, Surface waves and free oscillations

Identifiers

Local EPrints ID: 457076
URI: http://eprints.soton.ac.uk/id/eprint/457076
ISSN: 0956-540X
PURE UUID: cdee7072-0601-4fd3-883f-75a40afdda36
ORCID for Derek Keir: ORCID iD orcid.org/0000-0001-8787-8446

Catalogue record

Date deposited: 23 May 2022 16:47
Last modified: 04 Oct 2022 01:44

Export record

Altmetrics

Contributors

Author: Emma L. Chambers
Author: Nick Harmon
Author: Kate Rychert
Author: Ryan J. Gallacher
Author: Derek Keir ORCID iD

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×