High-resolution spatio-temporal analysis reveals the dynamic evolution of earthquake swarms around Askja–Herðubreið, Northern Volcanic Zone Iceland

Earthquake swarms are a common expression of crustal deformation in volcanic, geothermal, and rift environments, yet the processes that govern their initiation, migration, and internal evolution remain uncertain. Many regions face limitations in catalog completeness and location accuracy, hindering the ability to resolve overlapping processes. Although newer detection techniques have improved swarm characterization, most studies focus on individual sequences. The Askja–Herðubreið region of the Northern Volcanic Zone (NVZ), one of Iceland’s most active swarm areas, offers an opportunity to examine swarm behavior across multiple sequences. This thesis applies matched-filter detection, relative relocation, and a structured post-processing workflow to construct fine-scale spatio-temporal catalogs for 31 swarms in the Askja–Herðubreið area between 2010 and 2020. The analysis emphasizes spatial and temporal evolution, including migration patterns, fault-plane geometries, and migration models parameterized by velocity or diffusivity. This approach improves their location precision to tens of meters and enhances completeness by an order of magnitude relative to routine catalogs. The resulting catalogs reveal diverse internal structures and dynamics. Swarms show linear and diffusive migration, depth transitions, multiple active fault segments, and localized aseismic channels. Several sequences display changes in migration style (diffusive to linear) through time, indicating that multiple processes can operate sequentially or concurrently. These results show that fine-scale spatio-temporal analysis is essential for resolving the internal dynamics of earthquake swarms in Icelandic rift environments. By documenting the range of migration processes in the Askja–Herðubreið region, the thesis provides observations relevant to models involving fluid pressure changes, fault-zone heterogeneity, and aseismic slip, and establishes a framework for comparative swarm studies in other tectonic settings.