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

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Title: Tremor-rich shallow dyke formation followed by silent magma flow at Bárðarbunga in Iceland
Authors: Eibl, Eva P. S.
Bean, Christopher J.
Vogfjörð, Kristín
Ying, Yingzi
Lokmer, Ivan
Möllhoff, Martin
O'Brien, G. S.
Pálsson, Finur
Permanent link: http://hdl.handle.net/10197/8740
Date: Apr-2017
Abstract: The Bárðarbunga eruption in Iceland in 2014 and 2015 produced about 1.6 km3 of lava. Magma propagated away from Bárðarbunga to a distance of 48 km in the subsurface 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 Q.1 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 therelationships 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 Bárðarbunga 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. 
Funding Details: European Commission - Seventh Framework Programme (FP7)
Type of material: Journal Article
Publisher: Nature
Keywords: EarthquakesDyke propagationTremor modelsMagma flow
DOI: 10.1038/NGEO2906
Language: en
Status of Item: Peer reviewed
Appears in Collections:Earth Sciences Research Collection

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