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Mechanism for deep crustal seismicity: Insight from modeling of deformation process at the Main Ethiopian Rift

Mechanism for deep crustal seismicity: Insight from modeling of deformation process at the Main Ethiopian Rift
Mechanism for deep crustal seismicity: Insight from modeling of deformation process at the Main Ethiopian Rift
We combine numerical modeling of lithospheric extension with analysis of seismic moment release and earthquake b‐value in order to elucidate the mechanism for deep crustal seismicity and seismic swarms in the Main Ethiopian Rift (MER). We run 2D numerical simulations of lithospheric deformation calibrated by appropriate rheology and extensional history of the MER to simulate migration of deformation from mid‐Miocene border faults to ~30 km wide zone of Pliocene to recent rift floor faults. While the highest strain rate is localized in a narrow zone within the rift axis, brittle strain has been accumulated in a wide region of the rift. The magnitude of deviatoric stress shows strong variation with depth. The uppermost crust deforms with maximum stress of 80 MPa, at 8‐14 km depth stress sharply decreases to 10 MPa and then increases to a maximum of 160 MPa at ~18 km depth. These 2 peaks at which the crust deforms with maximum stress of 80 MPa or above correspond to peaks in the seismic moment release. Correspondingly, the drop in stress at 8‐14 km correlates to a low in seismic moment release. At this depth range, the crust is weaker and deformation is mainly accommodated in a ductile manner. We therefore see a good correlation between depths at which the crust is strong and elevated seismic deformation, while regions where the crust is weaker deform more aseismically. Overall the bimodal depth distribution of seismic moment release is best explained by rheology of the deforming crust.
Main Ethiopian Rift, earthquakes, numerical modeling, strain rate
1525-2027
Muluneh, Ameha
9c48408f-650f-49ad-9133-bc201fa817ce
Brune, Sascha
2610fb89-af9e-4fae-8292-fac70ec15418
Illsley-Kemp, Finnigan
c24ef4cb-cbf9-4a58-af8d-da9c7eabd84d
Corti, Giacomo
dce88b12-5b7a-43b1-8a58-5bd1bc13634c
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Glerum, Anne
131ed971-6cf8-48c2-9c8a-2f26aada1676
Kidane, Tesfaye
57285951-0004-4d5f-92ce-c4690c7ae813
Mori, Jim
763641e4-ceea-4369-a914-cc713d85fee9
Muluneh, Ameha
9c48408f-650f-49ad-9133-bc201fa817ce
Brune, Sascha
2610fb89-af9e-4fae-8292-fac70ec15418
Illsley-Kemp, Finnigan
c24ef4cb-cbf9-4a58-af8d-da9c7eabd84d
Corti, Giacomo
dce88b12-5b7a-43b1-8a58-5bd1bc13634c
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Glerum, Anne
131ed971-6cf8-48c2-9c8a-2f26aada1676
Kidane, Tesfaye
57285951-0004-4d5f-92ce-c4690c7ae813
Mori, Jim
763641e4-ceea-4369-a914-cc713d85fee9

Muluneh, Ameha, Brune, Sascha, Illsley-Kemp, Finnigan, Corti, Giacomo, Keir, Derek, Glerum, Anne, Kidane, Tesfaye and Mori, Jim (2020) Mechanism for deep crustal seismicity: Insight from modeling of deformation process at the Main Ethiopian Rift. Geochemistry, Geophysics, Geosystems, 21 (7), [e2020GC008935]. (doi:10.1029/2020GC008935).

Record type: Article

Abstract

We combine numerical modeling of lithospheric extension with analysis of seismic moment release and earthquake b‐value in order to elucidate the mechanism for deep crustal seismicity and seismic swarms in the Main Ethiopian Rift (MER). We run 2D numerical simulations of lithospheric deformation calibrated by appropriate rheology and extensional history of the MER to simulate migration of deformation from mid‐Miocene border faults to ~30 km wide zone of Pliocene to recent rift floor faults. While the highest strain rate is localized in a narrow zone within the rift axis, brittle strain has been accumulated in a wide region of the rift. The magnitude of deviatoric stress shows strong variation with depth. The uppermost crust deforms with maximum stress of 80 MPa, at 8‐14 km depth stress sharply decreases to 10 MPa and then increases to a maximum of 160 MPa at ~18 km depth. These 2 peaks at which the crust deforms with maximum stress of 80 MPa or above correspond to peaks in the seismic moment release. Correspondingly, the drop in stress at 8‐14 km correlates to a low in seismic moment release. At this depth range, the crust is weaker and deformation is mainly accommodated in a ductile manner. We therefore see a good correlation between depths at which the crust is strong and elevated seismic deformation, while regions where the crust is weaker deform more aseismically. Overall the bimodal depth distribution of seismic moment release is best explained by rheology of the deforming crust.

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2020GC008935 - Accepted Manuscript
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e-pub ahead of print date: 9 June 2020
Keywords: Main Ethiopian Rift, earthquakes, numerical modeling, strain rate

Identifiers

Local EPrints ID: 441912
URI: http://eprints.soton.ac.uk/id/eprint/441912
ISSN: 1525-2027
PURE UUID: c05cfa73-cc80-433a-8922-d8a00326ebe6
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

Catalogue record

Date deposited: 02 Jul 2020 16:30
Last modified: 22 Nov 2021 03:01

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Contributors

Author: Ameha Muluneh
Author: Sascha Brune
Author: Finnigan Illsley-Kemp ORCID iD
Author: Giacomo Corti
Author: Derek Keir ORCID iD
Author: Anne Glerum
Author: Tesfaye Kidane
Author: Jim Mori

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