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Magma-fluid interactions beneath the Akutan Volcano in Aleutian Arc based on the results of local earthquake tomography
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  • Koulakov Ivan,
  • Viktoria Komzeleva,
  • Sergey Z. Smirnov,
  • Bortnikova Svetlana B.
Koulakov Ivan
Trofimuk Institute of Petroleum Geology and Geophysics, SB RAS

Corresponding Author:[email protected]

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Viktoria Komzeleva
Trofimuk Institute of Petroleum Geology and Geophysics SB RAS
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Sergey Z. Smirnov
Sobolev Institute of Geology and Mineralogy SB RAS
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Bortnikova Svetlana B.
Trofimuk Institute of Petroleum Geology and Geophysics SB RAS
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Abstract

Akutan Island hosts a volcano considered as one of most active in the Aleutians Arc. Besides the regular eruption activity, Akutan in 1996 experienced a remarkable seismic unrest with earthquakes reaching the magnitude of M 5.3. We build a new tomography model including the 3D distributions of the , and ratio based on arrival time data from more than 4000 local earthquakes. In this model, we reveal a columnar anomaly of high ratio with the top boundary at a depth of 5-6 km below surface, which represents a steady conduit feeding the Akutan volcano. At a depth of ~4 km, the deep conduit is split in two branches, one of which ascend to the summit area and another one directs to a fumarole field at the flank of the volcano. This structure explains distinct geochemical features of emitted gases in these two areas. In the upper part of the velocity model, the highly heterogeneous structures are associated with interactions of shallow magmatic sources, meteoric and magmatic fluids, as well as degassing. Besides the prominent anomaly associated with the shallow magma reservoir beneath the caldera and the active cone, we observe several areas with high ratio, some of which are interpreted as shallow magma storages, and some as zones of meteoric water penetration. We propose a scenario of abrupt fluid ejection from the deep magma conduit that led to the seismic unrest and strong ground deformations in the Akutan area in 1996.
Mar 2021Published in Journal of Geophysical Research: Solid Earth volume 126 issue 3. 10.1029/2020JB021192