The Use of Simple Physical Models in Seismology and Glaciology

Abstract

In this thesis, I present results that span a number of largely independent topics within the broader disciplines of seismology and glaciology. The problems addressed in each section are quite different, but the approach taken throughout is to use simplified models to attempt to understand more complex physical systems. In these models, use of solid and fluid mechanics are important elements, though in some cases the mechanics are greatly simplified so that progress can be more easily made. The five primary results of this thesis can be summarized as follows: (1) Glacial earthquakes, which were known as enigmatic M_S ~ 5 seismic sources prior to the work presented here, are now characterized and understood as being due to coupling of gravitational energy from large calving icebergs into the solid Earth. (2) Rapid drainage events from meltwater lakes on Greenland can be understood in terms of models of turbulent hydraulic fracture at the base of the Greenland Ice Sheet. (3) The form of ‘lake star’ melt patterns on lake ice can be quantitatively modeled as arising from flow of warm water through slushy ice. (4) The 2004 Sumatra earthquake can be approximated using a 5-point rupture model, and this model helps resolve some uncertainties of previous models. (5) The accuracy of seismic noise tomography results can be better understood and calculated through use of a new theoretical approach. While there is no overarching theme to the results obtained in this thesis, all results represent an increase in our understanding of some area of geophysics.