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Local seismicity near the actively deforming Corbetti volcano in the Main Ethiopian Rift

Local seismicity near the actively deforming Corbetti volcano in the Main Ethiopian Rift
Local seismicity near the actively deforming Corbetti volcano in the Main Ethiopian Rift
Corbetti is currently one of the fastest uplifting volcanoes globally, with strong evidence from geodetic and gravity data for a subsurface inflating magma body. A dense network of 18 stations has been deployed around Corbetti and Hawassa calderas between February 2016 and October 2017, to place seismic constraints on the magmatic, hydrothermal and tectonic processes in the region. We locate 122 events of magnitudes between 0.4 and 4.2 using a new local velocity model. The seismicity is focused in two areas: directly beneath Corbetti caldera and beneath the city of Hawassa. The shallower 0–5 km depth below sea level (b.s.l.) earthquakes beneath Corbetti are mainly focused in EW- to NS-elongated clusters at Urji and Chabbi volcanic centres. This distribution is interpreted to be mainly controlled by a northward propagation of hydrothermal fluids away from a cross-rift pre-existing fault. Source mechanisms are predominantly strike-slip and different to the normal faulting away from the volcano, suggesting a local rotation of the stress-field. These observations, along with a low Vp/Vs ratio, are consistent with the inflation of a gas-rich sill, likely of silicic composition, beneath Corbetti. In contrast, the seismicity beneath Hawassa extends to greater depth (16 km b.s.l.). These earthquakes are focused on 8–10 km long segmented faults, which are active in seismic swarms. One of these swarms, in August 2016, is focused between 5 and 16 km depth b.s.l. along a steep normal fault beneath the city of Hawassa, highlighting the earthquake hazard for the local population.
0377-0273
227-237
Lavayssiere, Aude
4754825b-d4c7-45ec-b715-b46a7c92f042
Greenfield, Timothy
be593d17-54a8-4c18-ac57-9ce1bfe3920f
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Ayele, Atalay
5b4eeb35-d229-4325-8940-d934dab7563d
Kendall, J-Michael
0a1d10dd-0a0a-4b02-aefd-cde8741307ce
Lavayssiere, Aude
4754825b-d4c7-45ec-b715-b46a7c92f042
Greenfield, Timothy
be593d17-54a8-4c18-ac57-9ce1bfe3920f
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Ayele, Atalay
5b4eeb35-d229-4325-8940-d934dab7563d
Kendall, J-Michael
0a1d10dd-0a0a-4b02-aefd-cde8741307ce

Lavayssiere, Aude, Greenfield, Timothy, Keir, Derek, Ayele, Atalay and Kendall, J-Michael (2019) Local seismicity near the actively deforming Corbetti volcano in the Main Ethiopian Rift. Journal of Volcanology and Geothermal Research, 381, 227-237. (doi:10.1016/j.jvolgeores.2019.06.008).

Record type: Article

Abstract

Corbetti is currently one of the fastest uplifting volcanoes globally, with strong evidence from geodetic and gravity data for a subsurface inflating magma body. A dense network of 18 stations has been deployed around Corbetti and Hawassa calderas between February 2016 and October 2017, to place seismic constraints on the magmatic, hydrothermal and tectonic processes in the region. We locate 122 events of magnitudes between 0.4 and 4.2 using a new local velocity model. The seismicity is focused in two areas: directly beneath Corbetti caldera and beneath the city of Hawassa. The shallower 0–5 km depth below sea level (b.s.l.) earthquakes beneath Corbetti are mainly focused in EW- to NS-elongated clusters at Urji and Chabbi volcanic centres. This distribution is interpreted to be mainly controlled by a northward propagation of hydrothermal fluids away from a cross-rift pre-existing fault. Source mechanisms are predominantly strike-slip and different to the normal faulting away from the volcano, suggesting a local rotation of the stress-field. These observations, along with a low Vp/Vs ratio, are consistent with the inflation of a gas-rich sill, likely of silicic composition, beneath Corbetti. In contrast, the seismicity beneath Hawassa extends to greater depth (16 km b.s.l.). These earthquakes are focused on 8–10 km long segmented faults, which are active in seismic swarms. One of these swarms, in August 2016, is focused between 5 and 16 km depth b.s.l. along a steep normal fault beneath the city of Hawassa, highlighting the earthquake hazard for the local population.

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More information

Accepted/In Press date: 12 June 2019
e-pub ahead of print date: 17 June 2019
Published date: 1 September 2019

Identifiers

Local EPrints ID: 432002
URI: https://eprints.soton.ac.uk/id/eprint/432002
ISSN: 0377-0273
PURE UUID: d9f34e9a-0afa-471f-9b95-3fe8e2b5c1f3
ORCID for Timothy Greenfield: ORCID iD orcid.org/0000-0002-4370-7298
ORCID for Derek Keir: ORCID iD orcid.org/0000-0001-8787-8446

Catalogue record

Date deposited: 26 Jun 2019 16:30
Last modified: 03 Sep 2019 00:44

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Contributors

Author: Aude Lavayssiere
Author: Timothy Greenfield ORCID iD
Author: Derek Keir ORCID iD
Author: Atalay Ayele
Author: J-Michael Kendall

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