Improving our understanding of glacial sliding is crucial for
constraining basal drag in ice dynamics models. We use icequakes, sudden
releases of seismic energy as the ice slides over the bed, to provide
geophysical observations that can be used to aid understanding of the
physics of glacial sliding and constrain ice dynamics models. These
icequakes are located at the bed of an alpine glacier in Switzerland and
the Rutford Ice Stream, West Antarctica, two extremes of glacial
settings and spatial scales. We investigate a number of possible
icequake source mechanisms by performing full waveform inversions to
constrain the fundamental physics and stress release during an icequake
stick-slip event. Results show that double-couple mechanisms best
describe the source for the events from both glacial settings and the
icequakes originate at or very near the ice-bed interface. We also
present an exploratory method for attempting to measure the till shear
modulus, if indirect, reflected icequake radiation is observed. The
results of this study increase our understanding of how icequakes are
associated with basal drag while also providing the foundation for a
method of remotely measuring bed shear strength.