Doctoral defence in Geophysics - Yilin Yang

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Doctoral candidate: Yilin Yang

Title of thesis: Volcano-tectonic Controls on Ground Deformation across Temporal Scales: Insights from the Krafla Volcanic System, Iceland

Opponents:
Dr. Corné Kreemer, Professor, University of Nevada, Reno, USA
Dr. Raphaël Grandin, Associate Professor at the Institut de Physique du Globe de Paris, Université Paris Cité, France

Advisor: Dr. Freysteinn Sigmundsson, Research Professor at the Institute of Earth Sciences, University of Iceland

Other members of the doctoral committee:
Dr. Halldór Geirsson, Professor at the Faculty of Earth Sciences, University of Iceland
Dr. Joachim Gottsmann, Researcher at the Department of Earth and Environmental Sciences, Ludwig‐Maximilians‐Universität München, Germany
Dr. Vincent Drouin, Specialist at Icelandic Meteorological Office

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

Abstract

Measurements of ground movements in volcanic regions and interpretation of observed deformation is important for understanding of volcano behavior and their subsurface processes. Observed deformation often reflects the combined effects of multiple processes. The Krafla volcanic system in North Iceland lies at the divergent plate boundary between the North American and Eurasian plates. A rifting episode in 1975–1984, five decades of geothermal exploitation and extensive geodetic observations make Krafla an ideal natural laboratory to investigate volcano deformation across multiple temporal scales and explore underlying geophysical processes. For short-term deformation, a period of accelerated westward motion during 2014–2015 at Krafla is identified from Global Navigation Satellite System (GNSS) time series using Bayesian inference. These deformation anomalies occurred concurrently with the near-field precursors of the 2014 Bárdarbunga dike intrusion, ~120 km to the south, indicating potential coupling between volcanic systems along the rift. For the decadal deformation associated with the 1975–1984 rifting episode, a revised numerical model of repeated dike intrusions is developed to incorporate realistic dike geometries and crustal behavior. The model reproduces first-order regularities of the 1975–1984 dike sequence and highlights the critical role of tectonic stress and topography in driving lateral dike propagation, allowing magma flow into dikes or eruptions under low pressure. For long-term deformation, velocity fields derived from GNSS (2002–2024) and Interferometric Synthetic Aperture Radar (InSAR; 2015–2023) constrain a six-segment plate boundary model for central Krafla. The inferred plate boundary central axis follows recent eruptive fissures and aligns with mapped fracture orientations. Locking depth variation along the fissure swarm implies a dome-shaped rheological transition. Residual velocities reveal three local deflation patterns related to geothermal activity and lava subsidence. Together, these results advance understanding of volcano-tectonic interactions at divergent plate boundaries, while the methodological developments have broader practical value.

About the doctoral candidate

Yilin Yang was born in 1996 in Fujian Province, China. He received his Bachelor’s degree in Geodesy and Geomatics Engineering in 2018 and his Master’s degree in Geodesy and Survey Engineering in 2021, both from the School of Geodesy and Geomatics, Wuhan University, China. After his Master’s studies, he worked as an assistant engineer at Wuhan University from 2021 to 2022. In May 2022, he began his Ph.D. studies in Geophysics at the University of Iceland under the European Training Network IMPROVE. During his doctoral research, he conducted secondments as a visiting Ph.D. student at the School of Earth Sciences, University of Bristol (four months in total), and at INGV Catania (two months in total), and undertook a three-week research internship at the Earthquake Research Institute, University of Tokyo.