Multi-scale seismic imaging and related seismicity patterns of Krafla volcano and its geothermal system

Krafla, one of the five central volcanoes of the Northern Volcanic Zone in NE-Iceland, last erupted during the Krafla Fires in the 70s and 80s. During the same period, a geothermal power plant was built within Krafla caldera, first operated in 1978. Both scientific and industrial interest led to an increase of knowledge of the complex system through systematic exploration with a wide variety of geophysical methods including seismic and electromagnetics coupled with borehole information.Among them, a local seismic network operated by Landsvirkjun and Iceland GeoSurvey, comprising 12 permanent broadband stations, has been continuously recording seismic data since 2013. We supplemented this network in June 2022 with a dense network of 98 nodes, resulting in two arrays, one large-scale, the other small-scale, operating in parallel.Here we present multi-scale 3-D velocity models for P-, S- and surface waves, independently derived for both networks through local earthquake and ambient noise tomographies. These models offer a glimpse into the subsurface structures of the volcanic system by utilizing various types of waves that are responsive to distinct rock/fluid properties and depths. The relocated and clustered seismic activity, documented by both permanent and temporary networks, underscores active structures pinpointed through tomography. With this we hope to strengthen the understanding of the connected volcanic and geothermal systems. Indeed, both the seismicity and strong velocity anomalies are located at similar depths as the magma batch that was drilled into with the IDDP1.