The 2014-15 Bárðarbunga-Holuhraun magmatic rifting episode: A seismic study
View / Open Files
Authors
Advisors
White, Robert S
Date
2018-11-24Awarding Institution
University of Cambridge
Author Affiliation
Earth Sciences
Qualification
Doctor of Philosophy (PhD)
Language
English
Type
Thesis
Metadata
Show full item recordCitation
Agustsdottir, T. (2018). The 2014-15 Bárðarbunga-Holuhraun magmatic rifting episode: A seismic study (Doctoral thesis). https://doi.org/10.17863/CAM.27047
Abstract
On 16 August 2014 an unusual sequence of earthquakes began near the southeastern rim
of the ice-covered Bárðarbunga caldera in central Iceland. Over the course of two weeks
a dyke propagated 48 km beneath the glacier northeastwards and into the Holuhraun lava
field, where it erupted for six months, becoming the largest eruption in Iceland for over 200
years. During this time, a gradual, incremental caldera collapse took place in the central
volcano. The rifting episode was captured both geodetically and seismically. In this thesis,
I analyse the seismic response to the event, both due to the dyke propagation, and the
subsequent caldera collapse. This gives an insight into the underlying processes controlling
rifting events, and the nature of the responding crust.
The Cambridge seismic network recorded the 2014-15 Bárðarbunga-Holuhraun rifting
episode in exceptional detail. I discuss the deployment and operation of this dense seismic
network in the remote Icelandic highlands, as well as the campaign deployments on the
volcano caldera, on the glacier (above the dyke path) and around the eventual eruption site,
as a first response to the crisis. Using this dataset I have accurately located, and analysed,
47,000 earthquakes during the pre-intrusive, intrusive, eruptive and post-eruptive periods.
Approximately 4,000 of the recorded earthquakes are associated with the caldera collapse,
delineating faults accommodating the subsidence and showing good correlation with
geodetic data. The seismicity reveals activation of both inner and outer caldera faults with
60 inward dipping planes on the northern and southern side, indicating a symmetric
caldera structure. Detailed analysis of the earthquake source mechanisms shows that 90%
can be explained by a double-couple solution, which is in contrast to results from previous
studies of Bárðarbunga. I find the dominant failure mechanism during the collapse to be
steep normal faulting, with sub-vertical P-axes, striking sub-parallel to the caldera rim. The
northern and southern sides of the caldera, however experienced very different seismicity
rates, highlighted by the order of magnitude difference in the cumulative seismic moments.
The southeastern part of the caldera, whilst experiencing less activity, shows a mixture of
failure mechanisms, owing to the interaction of the caldera collapse and the dyke exit. Therefore,
this thesis presents evidence of a complex asymmetric caldera collapse, not controlled
by a single caldera ring fault.
Of the 47,000 earthquakes located, 31,000 delineate the segmented, lateral dyke
intrusion as it fractured a pathway through the crust, utilizing pre-existing weaknesses.
Despite the extensional rift setting, the dyke emplacement generated exclusively doublecouple
earthquakes. At the leading edge of the propagation, earthquake source mechanisms show exclusively strike-slip faulting, in contrast to the conventional model of normal faulting
above a propagating dyke. I observe right-lateral strike-slip faulting as the dyke propagates
to the NE, and an abrupt change to left-lateral strike-slip faulting as the dyke turns and
propagates in a more northerly direction into the northern volcanic zone. This shows that
the direction of fault motion is determined by the opening of the dyke, rather than by the
regional extension.
I am also able to define the thickness of the seismogenic crust under Bárðarbunga as
7 km, based on the depth extent of observed seismicity. The bulk of the seismicity in the
volcano is located at 1-4 km below the surface, whereas the dyke exited the caldera at 4-6
km depth, propagating at 6-8 km b.s.l. I hypothesise that the magma storage region is
likely located at 4-6 km b.s.l. (6-8 km below the caldera surface), just below the most active
caldera seismicity and at similar depth levels to the dyke. Thus, this thesis details the melt
distribution and movement at depth from a large basaltic central volcano, and the coupled
deformation of the subsiding caldera with the dyke intrusion and eruption.
Keywords
rifting event, Iceland, dyke propagation, caldera collapse, Holuhraun, Bárðarbunga, seismology, volcanology
Identifiers
This record's DOI: https://doi.org/10.17863/CAM.27047
Rights
All rights reserved, All Rights Reserved
Licence URL: https://www.rioxx.net/licenses/all-rights-reserved/
Statistics
Total file downloads (since January 2020). For more information on metrics see the
IRUS guide.
Recommended or similar items
The current recommendation prototype on the Apollo Repository will be turned off on 03 February 2023. Although the pilot has been fruitful for both parties, the service provider IKVA is focusing on horizon scanning products and so the recommender service can no longer be supported. We recognise the importance of recommender services in supporting research discovery and are evaluating offerings from other service providers. If you would like to offer feedback on this decision please contact us on: support@repository.cam.ac.uk