Seismic Imaging of the Reykjanes Peninsula, Iceland: Crustal‐Scale Context of Geothermal Areas and Ongoing Volcano‐Tectonic Unrest

Abstract Volcanic and seismic unrest on the Reykjanes Peninsula in SW Iceland that started in late 2019 after ∼800 years of quiescence has drawn wide interest to this on‐land extension of the Mid‐Atlantic spreading ridge. Here, we use seismic data collected across the larger Peninsula region, covering six volcanic systems and associated high‐temperature geothermal areas to produce a crustal‐scale shear‐wave velocity model. The model is constructed from receiver functions (RF), and pre‐existing surface wave dispersion measurements from recent studies, supplemented with new inter‐station paths from recent seismic deployments. We compare our velocity model to RF stacks which highlight seismic discontinuity boundaries. Results show local seismicity and geothermal systems are limited to the upper crust, which is split into an upper region of extrusive‐dominated heavily fractured material <3 km and intrusive‐dominated more cohesive material below. The gabbroic lower‐crust is dominated by cumulates beyond 10 km depth, which are particularly high‐velocity west offshore of the Peninsula. Crustal thicknesses increase from 15 to 20 km eastwards, likely reflecting increasing temperature and active‐upwelling toward the center of the Iceland hotspot. Reported magma storage depths, for current and historic eruptions, generally sit within the lower‐crust, but several, including for the 2021 Fagradalsfjall eruption, indicate sub‐Moho storage, sourced from a seismically slow region we observe extending to 25 km, which is interpreted as representing a partially molten crust‐mantle transitional region. Our seismic imaging of the Reykjanes Peninsula crust gives insight into regional crustal structure and tectonic processes, as well as providing large‐scale context for the continuing volcano‐tectonic unrest the region is experiencing.