Seismic Efficiency during Volcanic Unrest: Insights from the 2010 Eyjafjallajökull Eruption

James Hallam Dalziel , Juliet Biggs, Maximilian Jonas Werner, Heidy Mader

Identifying patterns in precursory signals may aid forecasting over month to year timescales. We examine the relationship between seismicity and ground deformation during unrest prior to the 2010 Eyjafjallajökull eruption, finding the ratio between seismic moment and horizontal GPS ground displacement is constant within two distinct phases, with a step increase from one to the other. This is attributed to a change in source between two sills, and is expected given changes in deformation associated with different source geometries and growth mechanisms. We use displacement data to estimate source volume change, assuming each source has a fixed geometry through time. We then calculate seismic efficiency (the ratio between seismic moment and volume change, assuming a constant shear modulus), noting an increase between sources reflecting different growth mechanisms. The shallower source has a lower proportion of aseismic deformation, consistent with observations showing clusters of seismic events interpreted as magmatic ‘lobes’ separated by seismogenic zones. This case study provides new insights into subsurface processes prior to eruptive activity, specifically controls on the seismic efficiency of intrusions.