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Seismicity during continental breakup in the Red Sea rift of Northern Afar

Seismicity during continental breakup in the Red Sea rift of Northern Afar
Seismicity during continental breakup in the Red Sea rift of Northern Afar
Continental rifting is a fundamental component of plate tectonics. Recent studies have highlighted the importance of magmatic activity in accommodating extension during late-stage rifting, yet the mechanisms by which crustal thinning occurs are less clear. The Red Sea rift in Northern Afar presents an opportunity to study the final stages of continental rifting as these active processes are exposed sub-aerially. Between February 2011 and February 2013 two seismic networks were installed in Ethiopia and Eritrea. We locate 4951 earthquakes, classify them by frequency content and calculate 31 focal mechanisms. Results show that seismicity is focused at the rift axis and the western marginal graben. Rift axis seismicity accounts for ∼64% of the seismic moment release and exhibits a swarm-like behavior. In contrast, seismicity at the marginal graben is characterized by high-frequency earthquakes that occur at a constant rate. Results suggest that the rift axis remains the primary locus of seismicity. Low frequency earthquakes, indicative of magmatic activity, highlight the presence of a magma complex ∼12 km beneath Alu-Dalafilla at the rift axis. Seismicity at the marginal graben predominantly occurs on westward dipping, antithetic faults. Focal mechanisms show that this seismicity is accommodating E-W extension. We suggest that the seismic activity at the marginal graben is either caused by upper crustal faulting accommodating enhanced crustal thinning beneath Northern Afar, or as a result of flexural faulting between the rift and plateau. This seismicity is occurring in conjunction with magmatic extension at the rift axis, which accommodates the majority of long-term extension.
2169-9356
1-18
Illsley-Kemp, Finnigan
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Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Bull, Jonathan
974037fd-544b-458f-98cc-ce8eca89e3c8
Gernon, Thomas
658041a0-fdd1-4516-85f4-98895a39235e
Ebinger, Cynthia
9aab3b18-294f-4cda-b64d-375b1cae85bb
Hammond, James O.S.
ef58f4e9-e193-4920-8643-21782487db87
Kendall, J.-Michael
a747df8f-6522-4ca5-85e9-b100a7ede318
Goitom, Berhe
2dcaea8e-cdd3-4b05-a4a0-04481da83881
Ayele, Atalay
5b4eeb35-d229-4325-8940-d934dab7563d
Belachew, Manahloh
7ee40db0-a3cc-40d0-805b-97ce19d6e4df
Illsley-Kemp, Finnigan
c24ef4cb-cbf9-4a58-af8d-da9c7eabd84d
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Bull, Jonathan
974037fd-544b-458f-98cc-ce8eca89e3c8
Gernon, Thomas
658041a0-fdd1-4516-85f4-98895a39235e
Ebinger, Cynthia
9aab3b18-294f-4cda-b64d-375b1cae85bb
Hammond, James O.S.
ef58f4e9-e193-4920-8643-21782487db87
Kendall, J.-Michael
a747df8f-6522-4ca5-85e9-b100a7ede318
Goitom, Berhe
2dcaea8e-cdd3-4b05-a4a0-04481da83881
Ayele, Atalay
5b4eeb35-d229-4325-8940-d934dab7563d
Belachew, Manahloh
7ee40db0-a3cc-40d0-805b-97ce19d6e4df

Illsley-Kemp, Finnigan, Keir, Derek, Bull, Jonathan, Gernon, Thomas, Ebinger, Cynthia, Hammond, James O.S., Kendall, J.-Michael, Goitom, Berhe, Ayele, Atalay and Belachew, Manahloh (2018) Seismicity during continental breakup in the Red Sea rift of Northern Afar. Journal of Geophysical Research: Solid Earth, 1-18. (doi:10.1002/2017JB014902).

Record type: Article

Abstract

Continental rifting is a fundamental component of plate tectonics. Recent studies have highlighted the importance of magmatic activity in accommodating extension during late-stage rifting, yet the mechanisms by which crustal thinning occurs are less clear. The Red Sea rift in Northern Afar presents an opportunity to study the final stages of continental rifting as these active processes are exposed sub-aerially. Between February 2011 and February 2013 two seismic networks were installed in Ethiopia and Eritrea. We locate 4951 earthquakes, classify them by frequency content and calculate 31 focal mechanisms. Results show that seismicity is focused at the rift axis and the western marginal graben. Rift axis seismicity accounts for ∼64% of the seismic moment release and exhibits a swarm-like behavior. In contrast, seismicity at the marginal graben is characterized by high-frequency earthquakes that occur at a constant rate. Results suggest that the rift axis remains the primary locus of seismicity. Low frequency earthquakes, indicative of magmatic activity, highlight the presence of a magma complex ∼12 km beneath Alu-Dalafilla at the rift axis. Seismicity at the marginal graben predominantly occurs on westward dipping, antithetic faults. Focal mechanisms show that this seismicity is accommodating E-W extension. We suggest that the seismic activity at the marginal graben is either caused by upper crustal faulting accommodating enhanced crustal thinning beneath Northern Afar, or as a result of flexural faulting between the rift and plateau. This seismicity is occurring in conjunction with magmatic extension at the rift axis, which accommodates the majority of long-term extension.

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Accepted/In Press date: 24 February 2018
e-pub ahead of print date: 1 March 2018

Identifiers

Local EPrints ID: 418503
URI: http://eprints.soton.ac.uk/id/eprint/418503
ISSN: 2169-9356
PURE UUID: abbf82c9-a582-44f4-87bb-b1f3a083b347
ORCID for Finnigan Illsley-Kemp: ORCID iD orcid.org/0000-0002-7114-033X
ORCID for Derek Keir: ORCID iD orcid.org/0000-0001-8787-8446

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Date deposited: 09 Mar 2018 17:30
Last modified: 07 Oct 2020 01:59

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Contributors

Author: Finnigan Illsley-Kemp ORCID iD
Author: Derek Keir ORCID iD
Author: Jonathan Bull
Author: Thomas Gernon
Author: Cynthia Ebinger
Author: James O.S. Hammond
Author: J.-Michael Kendall
Author: Berhe Goitom
Author: Atalay Ayele
Author: Manahloh Belachew

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