Cracking into Cryoseismology

Abstract

The cryosphere encompasses the seasonally and perennially frozen parts of the earth and its extent is both sensitive to and impacts upon the global climate through surface energy and moisture fluxes and feedbacks. The dynamics of ice and frozen ground also impact directly on, e.g., construction and maintenance of roads in cold regions or transportation across floating ice sheets. The aim of this thesis was to investigate the extent to which seismic methods can be used to study dynamic processes and longer-term changes in the cryosphere. The thesis is structured around three case studies linking active- and passive-source seismic experiments with numerical models of thermal stress, seismic wave dispersion and propagation. In Paper 1, temporary arrays of geophones with fine spatial sampling demonstrated that high ground-ice content in the near-surface during winter/spring produces a seasonally varying multimodal surface wave dispersion pattern. In Paper 2, the role of thermal stress in triggering frost quakes was further explored using borehole temperature measurements and multi-decadal continuous seismic recordings from the small-aperture Spitsbergen seismic array (SPITS). Thermal contraction cracking within the frozen active layer was shown to be a plausible mechanism contributing to frost quake seismicity. In Paper 3, a multi-annual catalogue of explosive source seismic experiments conducted on first-year sea-ice in Van Mijenfjorden, Svalbard, was used to demonstrate the usefulness of air-coupled flexural waves for estimating the thickness of a floating ice sheet. Viewed as a whole, the case studies developed in this thesis illustrate the ability of seismic methods to record and monitor dynamic processes in the cryosphere over a range of temporal scales. Continuous passive seismic recordings with high-temporal resolution provide a useful complement to other geophysical and remote sensing techniques used for monitoring the dynamics of the cryosphere.