A detailed view of the magmatic plumbing system beneath Askja Volcano, Iceland, from ambient noise tomography 

The volcano Askja in the Northern Volcanic Zone (NVZ) of Iceland last erupted in 1961 and has been steadily deflating from the 1970s until August 2021 when GPS and InSAR measurements confirmed that it had begun re-inflating. The NVZ has hosted a network of seismic stations operated by the University of Cambridge Volcano Seismology group since 2006. In the summer of 2023, this network has been augmented by 12 three component nodes that will record for ~2 months in addition to 10 broadband instruments that will be left for a year in or around the caldera of Askja with an average station spacing of ~1-2 km. The combination of the long-term recordings from the backbone network during deflation and the more recent short-term dense recordings will provide a unique dataset to examine how this switch from deflation to inflation may effect the seismic velocity structure beneath the volcano, thereby providing new insight into the underlying magmatic system. In this study, we present preliminary results from the application of ambient noise tomography to this dataset to try and image any changes in the magmatic system, which will involve stacking different periods of ambient noise cross-correlations to obtain two sets of dispersion curves that are sensitive to the subsurface velocity structure beneath Askja prior to and following the switch to reinflation in August 2021. This allows us to produce 3D models of shear wave velocity that can be compared to help elucidate changes in the plumbing system that occurred due to this switch. The dense deployments in the caldera have the advantage of allowing us to measure dispersion curves to high frequencies due to the short interstation distances, which is expected to yield more information on shallow subsurface structure where GPS and InSAR measurements appear to indicate that the source of the inflation is concentrated.