Doctoral defense in Geophysics - Sara Sayyadi

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Doctoral candidate: Sara Sayyadi

Dissertation title: Geophysical constraints on the formation of the volcanic island of Surtsey in 1963-1967 and its internal structure.

Opponents: Dr. Michael Ort, Professor at the University of North Arizona and Dr. Stephen McNutt, Professor at the University of South Florida.

Advisor: Dr. Magnús Tumi Guðmundsson, Professor in Geophysics at the University of Iceland.

Doctoral committee: Dr. Páll Einarsson, Professor Emeritus, Faculty of Earth Sciences, UI and Dr. James D.L. White, Professor, University of Otago, New Zealand.

Chair of Ceremony: Dr. Andri Stefánsson, Professor and Head of Faculty at Earth Sciences at the University of Iceland.

Abstract

The volcanic island of Surtsey, off the south coast of Iceland, was formed in shallow ocean-emergent basaltic volcanism in 1963-1967. There were several episodes of activity, migrating between five vents (Surtur, Surtla, Surtungur, Syrtlingur and Jólnir) forming a discontinuous ~5.8 km-long mostly submarine ridge. Analysis of data from the rudimentary analog seismic network existing in Iceland the 1960s reveals that the magnitude of completeness for the Surtsey area was ML=2.5. Precursory seismicity (ML<3) is detected for nine days before onset of continuous tremor on 12 November 1963, signaling the onset of a 40-hour long submarine eruption, followed by subaerial explosive activity. Earthquakes during the eruption were mostly related to intrusive activity preceding opening of new vents. A complicated relationship emerges between seismic tremor and magma flow rate or style of activity. The highest magma flow rates in the first 10–20 days were associated with relatively low tremor; higher tremor was observed in the weeks that followed, after discharge rate had dropped substantially. No correlation is found between minutes-to-hours variations in explosive activity and tremor. A detailed aeromagnetic survey was conducted in 2021. Spectral analysis, Euler deconvolution and 2.5D forward modeling of selected profiles reveal shallow origin of magnetic anomalies in the area. The subaerial lavas on Surtsey cause the strongest anomalies, while other sources are mostly 0-300 m below seafloor. No indications of significant intrusions are found within and below the structures formed in 1963-1967, confirming that magma fragmentation was dominant in the submarine phases of the Surtsey eruption.

About the doctoral candidate

Sara obtained her bachelor's degree in physics, but then turned to geophysics and graduated with a master's degree from the University of Tehran. Sara came to Iceland in 2017 for her doctoral studies.