Seismic analysis of the 2014 Bárðarbuga-Holuhraun dyke intrusion

Thorbjörg Ágústsdóttir, Iceland GeoSurvey

Micro-earthquakes are often detected under and around volcanoes prior to an eruption, caused by melt movement at depth. Volcano seismology can therefore give valuable constraints of the plumbing system of a volcano. Studying the seismicity accompanying the 2014 Bárðarbuga-Holuhraun dyke intrusion, central Iceland, revealed a lateral intrusion that propagated episodically 48 km, over the course of two weeks before breaching the surface. The 6 months long eruption was fed from the subsiding Bárðarbunga caldera. The dense Cambridge seismic network provided an unprecedented insight into the rifting episode and associated caldera collapse, enabling accurate location-detection of over 40,000 earthquakes. The cumulative earthquake energy represents only 1% of the geodetic moment. This means that earthquakes can tell us where the magma is going, breaking it’s way through the crust, but not necessarily where it is flowing. Consequently, most of the magma flow was aseismic after a melt channel formed.

This unique data set enables investigating the earthquake source mechanisms, which are important to understand the dynamics of a rifting episode. In contrast to the conventional model we found the dyke earthquakes to be exclusively dyke parallel strike-slip faulting. The caldera earthquakes were found to be normal faulting parallel to the caldera rim, opposite to previous studies.

Thorbjorg Agustsdottir finished her PhD in volcano seismology from the University of Cambridge in December 2017, supervised by professor Robert S. White. She has just started working at Iceland GeoSurvey researching micro-earthquakes in geothermal areas. Follow Thorbjorg to find out more about her research and volcano love: @fencingtobba, and read her paper on the Bárðarbuga-Holuhraun dyke intrusion here: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2015GL067423