Seismic Network in the Underexplored Central Iceland (SNUCI): Investigating Local Seismicity in the Langjökull and Hofsjökull volcanic systems

The SNUCI seismic network was deployed in the Highlands of Central Iceland in July 2024, with the aim of investigating the crustal structure and local seismicity along the E-W aligned plate boundary segment between the Western and Eastern Volcanic rift Zones. The network consists of 15 broadband seismic sensors distributed over an area of ~75x150 km, surrounding the partially subglacial Langjökull and Hofsjökull volcanic systems. Complemented by stations operated by the Icelandic Meteorological Office and the University of Cambridge & University of Iceland, it is the densest local seismic array in the region to date and thus provides the opportunity to significantly improve our knowledge of crustal processes and monitor seismic activity within two large volcanic systems. Whereas the Langjökull system has exhibited sustained levels of seismicity detected by the national seismic monitoring network over the past decades, seismicity within the Hofsjökull system has increased markedly since 2020, prompting enhanced monitoring in the region.  

Here we present the seismic catalogue from the first year of the SNUCI deployment. Automated event detection, relative relocation and clustering analysis are applied to provide a detailed description of the seismicity distribution and event characteristics in different earthquake clusters. Source mechanisms for the highest-magnitude events are constrained by P-wave first-motion polarity inversion. The catalogue shows persistent seismicity both within and outside of the known volcanic systems. While most activity is concentrated in the shallow crust (<15 km), several deep event clusters are identified in the lower crust beneath the Hofsjökull volcanic system, extending down to ~30 km depth. Our new high-resolution dataset can provide novel insights into the ongoing volcano-tectonic processes in this understudied region.