AN AWAKENING MAGMATIC SYSTEM BENEATH THE UDINA VOLCANIC COMPLEX (Kamchatka): EVIDENCE FROM SEISMIC UNREST OF 2017-2019
Yu.A. Kugaenko1, V.A. Saltykov1, I.Yu. Koulakov2,3, V.M. Pavlov1, P.V. Voropaev1, I.F. Abkadyrov1,4, V.P. Komzeleva2
1Geophysical Survey of the Russian Academy of Sciences, Federal Research Center, bu’lv. Piipa 9, Petropavlovsk-Kamchatsky, 683006, Russia
2Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
3Novosibirsk State University, ul. Pirogova 1, Novosibirsk, 630090, Russia
4Institute of Volcanology and Seismology, Far Eastern Branch of the Russian Academy of Sciences, bu’lv. Piipa 9, Petropavlovsk-Kamchatsky, 683006, Russia
Keywords: Seismic activity, seismicity, volcano, magmatic system, Bolshaya Udina and Malaya Udina volcanoes, seismic tomography, long-period earthquakes
Abstract
The Udina volcanic complex located in the southeastern part of the Klyuchevskoy group of volcanoes in Kamchatka remained dormant for several thousand years, but the magmatic system beneath the area may be awakening judging by seismic unrest. Seismicity in the area is characterized by data from permanent regional seismic stations and campaign local stations, as well as by data of the Kamchatka earthquake catalog. Seismic activity having nucleated at shallow depths in the vicinities of the Udina volcanoes since October 2017 may reflect a beginning cycle of volcanism. The earthquakes are mainly long-period (LP) 0.5-5 Hz events, which are commonly attributed to the movement of viscous magma and resonance phenomena in magma conduits. Such earthquakes may be a response to inputs of new magma batches to the plumbing system that feeds the volcanoes and thus may be precursors of volcanic unrest. Seismic campaigns of May-July 2018 near the Udina complex provided more rigorous constraints on earthquake coordinates and origin depths and showed that most of the earthquakes originated within 5 km beneath the Bolshaya Udina Volcano. Seismic tomographic inversion using the LOTOS code revealed a zone of high P -wave velocities, low S -wave velocities, and a high vP / vS ratio directly beneath the volcano. Such a combination of parameters typically occurs in active volcanic areas and marks intrusion of partially molten magma and/or liquid fluids. The velocity anomaly detected in 2018 is shallower than that recovered in 2014-2015. The seismic evidence, along with the available geological and geophysical data, record the movement of viscous magma related to the Udina feeding system in the middle crust, which is implicit proof for connection between the intermediate crustal and deep mantle magma sources renewed after a long lull.
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