Strike-slip faulting during the 2014 Baroarbunga-Holuhraun dike intrusion, central Iceland

Over a 13day period magma propagated laterally from the subglacial Baroarbunga volcano in the northern rift zone, Iceland. It created >30,000 earthquakes at 5-7km depth along a 48km path before erupting on 29 August 2014. The seismicity, which tracked the dike propagation, advanced in short bursts at 0.3-4.7km/h separated by pauses of up to 81h. During each surge forward, seismicity behind the dike tip dropped. Moment tensor solutions from the leading edge show exclusively left-lateral strike-slip faulting subparallel to the advancing dike tip, releasing accumulated strain deficit in the brittle layer of the rift zone. Behind the leading edge, both left- and right-lateral strike-slip earthquakes are observed. The lack of non-double-couple earthquakes implies that the dike opening was aseismic. Key Points * Melt propagated 48km laterally at 5-7kmbsl prior to erupting, generating more than 30,000 earthquakes * Seismicity arises from double-couple strike-slip failure orientated subparallel to the dike strike * Left-lateral fault motion is dominant to accommodate extension across the divergent plate boundary