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Lower crustal earthquakes in the march 2018 sequence along the western margin of afar

Lower crustal earthquakes in the march 2018 sequence along the western margin of afar
Lower crustal earthquakes in the march 2018 sequence along the western margin of afar

During the evolution of continental rift systems, extension is thought to progressively focus in-rift to the future breakup boundary while faults along the rift margins progressively deactivate. However, observational constraints on how strain is partitioned between rift axis and rift margins are still lacking. The Afar rift records the latest stages of rifting and incipient continental breakup. Here, we analyzed the recent M W 5.2 earthquake on the Western Afar Margin on March 24, 2018 and the associated seismic sequence of >500 earthquakes using 24 temporary seismic stations deployed during 2017–2018. We show seismicity occurring at lower crustal depths, from ∼15 to ∼30 km, with focal mechanisms and relocated earthquakes highlighting both west-dipping and east-dipping normal faults. We tested earthquake depth using InSAR by processing six independent interferograms using Sentinel-1 data acquired from both ascending and descending tracks. None of them shows evidence of surface deformation. We tested possible ranges of depth by producing forward models for a fault located at progressively increasing depths. Models show that surface deformation is not significant for fault slip at depths greater than 15 km, in agreement with the hypocentral depth of 19 km derived from seismic data for the largest earthquake. Due to the localized nature of deep earthquakes near hot springs coupled with subsurface evidence for magmatism, we favor an interpretation of seismicity induced by migrating fluids such as magma or CO 2. We suggest that deep fluid migration can occur at the rifted-margin influencing seismicity during incipient continental rupture.

Afar, deep seismicity, rift margins
1525-2027
La Rosa, Alessandro
3443c440-23fe-437e-b908-80f6b923c4ba
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Doubre, Cecile
9f348925-f5b6-445c-8663-7f58f58b97f3
Sani, Federico
6c59b4c4-ecca-4ecc-ba2c-66efa5e5e3df
Corti, Giacomo
dce88b12-5b7a-43b1-8a58-5bd1bc13634c
Leroy, Sylvie
627c503b-1036-41fc-a24c-3d09954fab0a
Ayele, Atalay
5b4eeb35-d229-4325-8940-d934dab7563d
Pagli, Carolina
290edb22-712b-4563-a868-af4c21fdb6b0
La Rosa, Alessandro
3443c440-23fe-437e-b908-80f6b923c4ba
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Doubre, Cecile
9f348925-f5b6-445c-8663-7f58f58b97f3
Sani, Federico
6c59b4c4-ecca-4ecc-ba2c-66efa5e5e3df
Corti, Giacomo
dce88b12-5b7a-43b1-8a58-5bd1bc13634c
Leroy, Sylvie
627c503b-1036-41fc-a24c-3d09954fab0a
Ayele, Atalay
5b4eeb35-d229-4325-8940-d934dab7563d
Pagli, Carolina
290edb22-712b-4563-a868-af4c21fdb6b0

La Rosa, Alessandro, Keir, Derek, Doubre, Cecile, Sani, Federico, Corti, Giacomo, Leroy, Sylvie, Ayele, Atalay and Pagli, Carolina (2021) Lower crustal earthquakes in the march 2018 sequence along the western margin of afar. Geochemistry, Geophysics, Geosystems, 22 (4), [e2020GC009614]. (doi:10.1029/2020GC009614).

Record type: Article

Abstract

During the evolution of continental rift systems, extension is thought to progressively focus in-rift to the future breakup boundary while faults along the rift margins progressively deactivate. However, observational constraints on how strain is partitioned between rift axis and rift margins are still lacking. The Afar rift records the latest stages of rifting and incipient continental breakup. Here, we analyzed the recent M W 5.2 earthquake on the Western Afar Margin on March 24, 2018 and the associated seismic sequence of >500 earthquakes using 24 temporary seismic stations deployed during 2017–2018. We show seismicity occurring at lower crustal depths, from ∼15 to ∼30 km, with focal mechanisms and relocated earthquakes highlighting both west-dipping and east-dipping normal faults. We tested earthquake depth using InSAR by processing six independent interferograms using Sentinel-1 data acquired from both ascending and descending tracks. None of them shows evidence of surface deformation. We tested possible ranges of depth by producing forward models for a fault located at progressively increasing depths. Models show that surface deformation is not significant for fault slip at depths greater than 15 km, in agreement with the hypocentral depth of 19 km derived from seismic data for the largest earthquake. Due to the localized nature of deep earthquakes near hot springs coupled with subsurface evidence for magmatism, we favor an interpretation of seismicity induced by migrating fluids such as magma or CO 2. We suggest that deep fluid migration can occur at the rifted-margin influencing seismicity during incipient continental rupture.

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2020GC009614 - Accepted Manuscript
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Published date: 12 March 2021
Keywords: Afar, deep seismicity, rift margins

Identifiers

Local EPrints ID: 448961
URI: http://eprints.soton.ac.uk/id/eprint/448961
ISSN: 1525-2027
PURE UUID: b4ce4bfd-4637-4665-880e-a93e8403535d
ORCID for Derek Keir: ORCID iD orcid.org/0000-0001-8787-8446

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Date deposited: 12 May 2021 16:30
Last modified: 15 Sep 2021 01:57

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Contributors

Author: Alessandro La Rosa
Author: Derek Keir ORCID iD
Author: Cecile Doubre
Author: Federico Sani
Author: Giacomo Corti
Author: Sylvie Leroy
Author: Atalay Ayele
Author: Carolina Pagli

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