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

Nature Geoscience volume 10, pages 299–304 (2017)Cite this article

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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 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 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.

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Figure 1: Earthquake locations show the propagation of the dyke at depth.
Figure 2: Laterally moving and shallowing pre-eruptive tremor on 3 September 2014.
Figure 3: Projected back azimuth and amplitude location of the pre-eruptive tremor.
Figure 4: Comparison of real and synthetic tremor.
Figure 5: Tremor simulations indicate a tremor source depth of less than 2 km.

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Acknowledgements

The data were collected and analysed within the framework of FutureVolc, which has received funding from the European Union’s Seventh Programme for research, technological development and demonstration under grant agreement no. 308377. The Geological Survey of Ireland (GSI) provided additional financial support for field work. We thank B. H. Bergsson and H. Buxel for technical support, and M. H. Steinarsson and A. Braiden for support in the field. We are grateful to J. Almendros for helpful discussions and comments.

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Author notes

  1. Eva P. S. Eibl, Christopher J. Bean, Yingzi Ying & Martin Möllhoff

    Present address: Present address: Geophysics Section, School of Cosmic Physics, Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland.,

Authors and Affiliations

  1. School of Earth Sciences, University College Dublin, Belfield, Dublin 4, Ireland

    Eva P. S. Eibl, Christopher J. Bean, Yingzi Ying, Ivan Lokmer & Martin Möllhoff

  2. Icelandic Meteorological Office, Bústaðavegi 7–9, 108 Reykjavík, Iceland

    Kristín S. Vogfjörd

  3. Tullow Oil, Leopardstown, Dublin 18, Ireland

    Gareth S. O’Brien

  4. Institute of Earth Sciences, University of Iceland, Askja, Building of Natural Sciences, Sturlugata 7, 101 Reykjavík, Iceland

    Finnur Pálsson

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Contributions

E.P.S.E., C.J.B. and M.M. participated in instrument installation and data collection from seismometers in Iceland and analysing the data. E.P.S.E carried out processing including amplitude locations, array locations and tremor simulations. K.S.V. relocated earthquakes in the dyke and participated with E.P.S.E., C.J.B. and I.L. in the interpretation of the results. Numerical wavefield simulations were performed by Y.Y. on the basis of the topography provided by F.P. G.S.O’B. performed tremor simulations due to magma flow. All authors contributed to the preparation of the manuscript.

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Correspondence to Eva P. S. Eibl.

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Eibl, E., Bean, C., Vogfjörd, K. et al. Tremor-rich shallow dyke formation followed by silent magma flow at Bárðarbunga in Iceland. Nature Geosci 10, 299–304 (2017). https://doi.org/10.1038/ngeo2906

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