Tremor-rich shallow dyke formation followed by silent magma flow at Bárdarbunga in Iceland

Eibl, Eva P. S. and Bean, Christopher J. and Vogfjörd, Kristin S. and Ying, Yingzi and Lokmer, Ivan and Möllhoff, Martin and O'Brien, Gareth S. and Pálsson, Finnur (2017) Tremor-rich shallow dyke formation followed by silent magma flow at Bárdarbunga in Iceland. Nature Geoscience, 10 (4). pp. 299-304.

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Abstract

The Bárdarbunga eruption in Iceland in 2014 and 2015 produced about 1.6 km3 of lava. Magma propagated away from Bárdarbunga to a distance of 48 km in the sub-surface beneath Vatnajökull glacier, emerging a few kilometres beyond the glacier's northern rim. A puzzling observation is the lack of shallow (<3 km deep), high-frequency earthquakes associated with shallow dyke formation near the subaerial and subglacial eruptive sites, suggesting that near-surface dyke formation is seismically quiet. However, seismic array observations and seismic full wavefield simulations reveal the presence and nature of shallow, pre-eruptive, long-duration seismic tremor activity. Here we use analyses of seismic data to constrain the relationships between seismicity, tremor, dyke propagation and magma flow during the Bárðarbunga eruption. We show that although tremor is usually associated with magma flow in volcanic settings, pre-eruptive tremor at Bárdarbunga was probably caused by swarms of microseismic events during dyke formation, and hence is directly associated with fracturing of the upper 2–3 km of the crust. Subsequent magma flow in the newly formed shallow dyke was seismically silent, with almost a complete absence of seismicity or tremor. Hence, we suggest that the transition from temporarily isolated, large, deep earthquakes to many smaller, shallower, temporally overlapping earthquakes (< magnitude 2) that appear as continuous tremor announces the arrival of a dyke opening in the shallow crust, forming a pathway for silent magma flow to the Earth's surface.

Item Type:	Article
Uncontrolled Keywords:	Natural hazards Seismology Volcanology tremor
Divisions:	School of Cosmics Physics School of Cosmics Physics > Geophysics
Date Deposited:	05 Apr 2018 12:05
Last Modified:	20 Dec 2022 09:01
URI:	https://dair.dias.ie/id/eprint/384

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