Radiation from Directional Seismic Sources in Laterally Stratified Media with Application to Arctic Ice Cracking Noise

The formation of cracks in elastic media such as sea ice generates elastic waves in a radiation pattern being dependent on the actual fracture process and the stratification of the medium. In the case of horizontal stratification, this phenomenon can be idealized and mathematically modeled describing the directionality of the acoustic emission produced by compact cracks in such an environment. The thrust of the present research has been to develop an analytical and numerical model of the elastic wave field in range independent elastic environments for various seismic source mechanisms. The source types being considered are explosive sources, point forces, shear cracks, and tensile cracks. First, the compact source representations with fault surface in an arbitrary direction will be derived, and incorporated in a numerical model for propagation in stratified elastic media to yield the basic Green's function solution. This solution is then applied to derive the seismo-acoustic field produced by more complete cracking mechanisms, like non-compact and moving cracks. Finally, the effect of anisotropy on the acoustic emission, e.g. in sea ice and periodically fine layered sediments, will be considered. The developed model is applied to the ice cracking noise radiation in the central Arctic environment, and the characteristics of the field produced by different source and environmental parameters are discussed. The developed model can be applied to the source inversion problem, i.e. the characterization of the cracking mechanism from its acoustic emission with the purpose of obtaining a better understanding of the general ambient noise in the central Arctic. Another expected application is the development of remote sensing techniques suitable for the study of mechanical properties of ice. Thesis supervisor : Dr. Henrik Schmidt Associate Professor of Ocean Engineering