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Comparison of dike intrusions in an incipient seafloor-spreading segment in Afar, Ethiopia: Seismicity perspectives

Comparison of dike intrusions in an incipient seafloor-spreading segment in Afar, Ethiopia: Seismicity perspectives
Comparison of dike intrusions in an incipient seafloor-spreading segment in Afar, Ethiopia: Seismicity perspectives
Oceanic crust is accreted through the emplacement of dikes at spreading ridges, but the role of dike intrusion in plate boundary deformation during continental rupture remains poorly understood. Between 2005 and 2009 the ?70 km long Dabbahu?Manda Hararo rift segment in Ethiopia has experienced 14 large volume dike intrusions, 9 of which were recorded on temporary seismic arrays. A detailed comparison of the seismic characteristics of the seismically monitored dikes is presented with implications for dike intrusion processes and magmatic plumbing systems. All of the migrating swarms of earthquakes started from a <5 km radius zone at the middle of the Dabbahu?Manda Hararo segment, and traveled northward and southward along the rift axis. Small magnitude earthquakes associated with the margins of the propagating dike tips are followed by the largest magnitude, primarily low?frequency earthquakes. The seismic moment distributions show >80% of energy is released during the propagation phase, with minimal seismic energy release after the dike propagation ceases. We interpret that faulting and graben formation above the dikes occurs hours after the passage of the dike tip, coincident with the onset of low?frequency earthquakes. Dike lengths show no systematic reduction in length with time, suggesting that topographic loading and stress barriers influence dike length, as well as changes in tectonic stress. The propagation velocities of all the dikes follow a decaying exponential. Northward propagating dikes had faster average velocities than those that propagated southward, suggesting preconditioning by the 2005 megadike, or ongoing heating from a subcrustal magma source north of the midsegment.
0148-0227
B06405
Belachew, Manahloh
7ee40db0-a3cc-40d0-805b-97ce19d6e4df
Ebinger, C.
8d61032b-66e9-4a84-b2b9-450cb898ce92
Coté, D.
0e9e3194-5df2-4c72-9950-93255eaebadc
Keir, D.
5616f81f-bf1b-4678-a167-3160b5647c65
Rowland, J.V.
2202415e-5040-481b-adbd-f567021f4509
Hammond, J.O.S.
df081c77-2e69-4753-8846-549826d905bb
Ayele, A.
2a0d90e9-a4be-4484-9301-5c4df46f9407
Belachew, Manahloh
7ee40db0-a3cc-40d0-805b-97ce19d6e4df
Ebinger, C.
8d61032b-66e9-4a84-b2b9-450cb898ce92
Coté, D.
0e9e3194-5df2-4c72-9950-93255eaebadc
Keir, D.
5616f81f-bf1b-4678-a167-3160b5647c65
Rowland, J.V.
2202415e-5040-481b-adbd-f567021f4509
Hammond, J.O.S.
df081c77-2e69-4753-8846-549826d905bb
Ayele, A.
2a0d90e9-a4be-4484-9301-5c4df46f9407

Belachew, Manahloh, Ebinger, C., Coté, D., Keir, D., Rowland, J.V., Hammond, J.O.S. and Ayele, A. (2011) Comparison of dike intrusions in an incipient seafloor-spreading segment in Afar, Ethiopia: Seismicity perspectives. Journal of Geophysical Research, 116 (B6), B06405.

Record type: Article

Abstract

Oceanic crust is accreted through the emplacement of dikes at spreading ridges, but the role of dike intrusion in plate boundary deformation during continental rupture remains poorly understood. Between 2005 and 2009 the ?70 km long Dabbahu?Manda Hararo rift segment in Ethiopia has experienced 14 large volume dike intrusions, 9 of which were recorded on temporary seismic arrays. A detailed comparison of the seismic characteristics of the seismically monitored dikes is presented with implications for dike intrusion processes and magmatic plumbing systems. All of the migrating swarms of earthquakes started from a <5 km radius zone at the middle of the Dabbahu?Manda Hararo segment, and traveled northward and southward along the rift axis. Small magnitude earthquakes associated with the margins of the propagating dike tips are followed by the largest magnitude, primarily low?frequency earthquakes. The seismic moment distributions show >80% of energy is released during the propagation phase, with minimal seismic energy release after the dike propagation ceases. We interpret that faulting and graben formation above the dikes occurs hours after the passage of the dike tip, coincident with the onset of low?frequency earthquakes. Dike lengths show no systematic reduction in length with time, suggesting that topographic loading and stress barriers influence dike length, as well as changes in tectonic stress. The propagation velocities of all the dikes follow a decaying exponential. Northward propagating dikes had faster average velocities than those that propagated southward, suggesting preconditioning by the 2005 megadike, or ongoing heating from a subcrustal magma source north of the midsegment.

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Published date: 2011
Organisations: Geology & Geophysics

Identifiers

Local EPrints ID: 196903
URI: https://eprints.soton.ac.uk/id/eprint/196903
ISSN: 0148-0227
PURE UUID: e48e4ed7-6c5f-4090-89ee-75f5e5d39ce4
ORCID for D. Keir: ORCID iD orcid.org/0000-0001-8787-8446

Catalogue record

Date deposited: 14 Sep 2011 10:56
Last modified: 06 Jun 2018 12:31

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