Examining the relationship between seismic swarms and ground deformation during volcanic unrest

  • James Dalziel

Student thesis: Master's ThesisMaster of Science by Research (MScR)


Accurate volcano monitoring can be the key to saving lives, but although monitoring has improved in the past few decades there is still difficulty differentiating between certain volcanic processes. By analysing the relationship between different observable phenomena preceding eruption, we are better able to distinguish between magmatic, tectonic or hydrothermal activity. Identifying patterns in precursory signals may aid forecasting over month to year timescales. Here we examine the relationship between seismicity and ground deformation during unrest prior to the 2010 Eyjafjallajökull eruption. Unrest consisted of two phases associated with sills at different depths. We find that the ratio between seismic moment and horizontal GPS ground displacement is constant within each phase, but with a step increase from one to the other. This step-change is attributed to the change in source between two sills, and is expected given the change in deformation associated with different source geometries. Next, we use the displacement data to estimate source volume change, assuming each source has a fixed geometry through time. We can then calculate seismic efficiency (the ratio between seismic moment and volume change, assuming a constant shear modulus). An increase in seismic efficiency is also present between sources, indicating different growth mechanisms. The shallower source has a lower proportion of aseismic deformation, consistent with previous observations showing clusters of seismic events, interpreted as a number of magmatic ‘lobes’ separated by seismogenic zones. Finally, we plot seismic moment against volume change through time for each source to compare against previous studies of volcanic terrains. We find a power-law relationship for all sources, similar to unrest preceding the 2018 Sierra Negra eruption as well as past studies of volcanic eruptions and wastewater well injection. This case study provides new insights into subsurface processes prior to eruptive activity, specifically controls on the seismic efficiency of intrusions.
Date of Award6 Dec 2022
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorJuliet J Biggs (Supervisor), Heidy Mader (Supervisor) & Max Werner (Supervisor)

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