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Seismicity of the Bora - Tullu-Moye volcanic field, 2016-17

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Original languageEnglish
Pages (from-to)548-570
Number of pages23
JournalGeochemistry, Geophysics, Geosystems
Volume20
Issue number2
Early online date11 Dec 2018
DOIs
DateAccepted/In press - 19 Nov 2018
DateE-pub ahead of print - 11 Dec 2018
DatePublished (current) - Feb 2019

Abstract

The Bora ‐ Tullu‐Moye volcanic field is a geothermal energy prospect in the central Main Ethiopian Rift, but little is known about the seismicity of the region. Here we document seismic activity between Feb 2016 and Oct 2017, locating more than a 1000 seismic events of local magnitude 0 to 2.7. This provides new insights into fluid movement and deformation beneath what we only now realize is a complicated volcanic system. A discrete cluster of events lies beneath Tullu‐Moye (TM), but, surprisingly, most of the seismicity lies in two clusters that are beneath neither the Bora or TM edifices. In these regions, we use earthquake cluster orientations, fault‐plane‐solutions and fast seismic shear‐wave orientations to show that seismicity is triggered by hydrothermal circulation of fluids along pre‐existing fractures. The fractures trend in multiple directions and are, in general, not parallel to rifting related structures. Instead, the fractures are parallel to structures created during previous caldera forming eruptions at both Bora and TM. Highly fractured regions such as this could be attractive targets for geothermal power generation. We estimate a minimum depth for a magmatic body beneath TM to be 6.5 km using the mapped brittle‐ductile transition. Frequency analysis of the earthquake waveforms reveal the bulk of the events to be volcano‐tectonic but some low‐frequency (LF) seismicity is present at a depth of 5 km beneath the TM edifice triggered by high pore fluid pressures.

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    Rights statement: This is the final published version of the article (version of record). It first appeared online via Wiley at DOI: 10.1029/2018GC007648. Please refer to any applicable terms of use of the publisher.

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