Institute of Geophysics and Tectonics (IGT) PhD Projects
The Seismic S-wave structure of glaciers and ice sheets
Supervisors: Dr Roger Clark
Glaciers and ice sheets are a prominent casualty of climate change, with a consequent threat of sea-level rise – therefore, predicting their mechanical response is crucial in understanding the risk from climate change. The free water content of ‘warm ice’ (ice at the pressure melting point, usually found in the lower levels of many Alpine, Arctic, and other ice bodies) is pivotal in determining that response – but this physical property can’t be found by direct measurement. Instead, geophysical methods (highly developed for resource exploration) must be used. The propagation velocity and damping rate of electromagnetic (GPR) waves, acoustic (seismic P) waves, and shear (seismic S) waves are all sensitive to free water content. Most field studies deliver GPR or P-wave velocities alone: however, sufficiently accurate and precise estimates of free water content require values of several of these observables together. This project would, for the first time, evaluate 3 established methods for measuring S-wave speed: S-wave refraction/reflection surveys[1]; PS-converted reflection surveys[2]; and inversion of surface wave dispersion[3]. Each has challenges and attractions: difficult or easy fieldwork, complex or simple data reduction, good or poor resolution. Not all have been tried on cryosphere targets, and certainly not together on the same site: nor have they been integrated with each other, or with P-wave surveys easily done at the same time. This project would do so – and then assess the efficacy of adding seismic S-wave data to modelling of glacier and ice-sheet physical properties.
Suitable field areas can be accessed at modest cost – such as glaciers in the Alps, Sweden, and Svalbard (where informal agreement has been reached with Prof. Doug Benn at Longyearbyen, for logistic support). The School already owns the bulk of the necessary geophysical field equipment. Good working relationships have been established with other geophysical glaciology groups, and shared fieldwork is entirely possible.
[1] rarely done at any scale, only a few experimental surveys on cryosphere targets – relatively awkward fieldwork, potentially the best resolution
[2] state-of-the-art for the hydrocarbons industry, never done on cryosphere targets – relatively easy fieldwork but complex processing
[3] very well-developed in global-scale studies, little used for near-surface engineering targets, novel for cryosphere targets – easy fieldwork, relatively low resolution