An enhanced catalogue of ring fault seismicity at Bárðarbunga caldera since the start of the 2014 Holuhraun eruption

The 2014-2015 Bárðarbunga dike intrusion and caldera collapse, leading to the six-month Holuhraun eruption, featured more than 80 recurring M_w ≥ 5 earthquakes located on the caldera ring fault. The caldera floor, covered by the Vatnajökull ice cap, subsided by 65 meters during the eruptive period. Continuous monitoring using an extensive seismic network has shown evidence of fault slip reversal and repeating earthquakes. The sequence of moderate-sized ring fault earthquakes resumed in 2017, suggesting a continuation of the same type of fault slip behaviour in response to the reversal of the collapse.  

We re-examine the data prior and post fault slip reversal in the 2014-2016 period to improve our understanding of the processes governing the recurring earthquake sequence observed since the eruption starting in 2014. 

We use the seismic data collected since 2014 to build a new earthquake catalogue for the caldera ring fault. We use template matching to detect previously undetected low magnitude earthquakes. We developed a tailored data processing pipeline, leveraging the Icelandic HPC computing cluster and its GPU nodes, to optimize template matching and earthquake cross correlations, with an emphasis on finding repeating earthquakes on the caldera ring fault. We additionally carry out double difference relocation.  

We present an enhanced earthquake catalogue for the 2014-2016 period, with particular focus on the post-eruptive fault slip reversal, including a repeating earthquake analysis. We achieve a fourfold increase in the number of events in the catalogue and can detect events up to 1 M_L lower than the input catalogue. Using parallelisation, we can speed up our processing by up to 16 times on the HPC clusters. With new better-constrained catalogues generated using dense temporary networks from recent field campaigns, we are working towards improving locations for catalogues based on older data using double-difference relocation techniques.  

When the resurgence period is included, the Bárðarbunga caldera collapse event has effectively lasted for almost 12 years and includes more than 100 M_w ≥ 5 earthquakes. Re-examining older data with state-of-the-art processing techniques and computing resources offers a unique opportunity to build further context and aid holistic interpretation for the on-going events at the caldera, as well as to increase our broader understanding of faults undergoing large slip movements and the evolution of caldera collapse cycles.