Constraining Englacial Temperatures through Active Seismic Methods

1043675/Peters

This award supports a project to collect a vertical seismic profile along the WAIS Divide borehole. A seismic experiment of this type has never before been performed through glacial ice, and the seismic signals recorded at various depths within the ice column will yield detailed in situ information on the effects of temperature, c-axis fabric, and impurities on seismic wave propagation through the ice column when allied to the ongoing and proposed borehole logging and core measurements. The intellectual merit of this work is that it will lay the foundation for inferring the temperature profile of an ice column through active seismic methods. By correlating observed temperatures from the WAIS Divide borehole (a funded and scheduled experiment) to our seismic attenuation measurements, we will develop a proxy for determining temperature from englacial seismic reflections. Better temperature estimates would lead to improved ice sheet modeling and more accurate determinations of future ice sheet mass balance and sea level fluctuations. In addition, better constraints on the seismic properties of the ice column will lead to refined imaging of the subglacial environment and add to our understanding of the basal regime and its role in ice dynamics. These active seismic experiments at the WAIS Divide drilling site will also allow us to determine the remaining thickness of ice to the bed at WAIS Divide with high precision, as well as more accurately constrain the basal conditions and deeper geologic structure existing at WAIS Divide for potential sub-ice drilling. The broader impacts of the proposed work are that it has significant impacts beyond the field of glaciology. A surface-based technique for determining englacial temperatures within the ice sheet will provide better constraints on geothermal flux beneath ice sheets and glaciers. The seismic dataset could provide a valuable arena to test fundamental seismic wave propagation algorithms: in particular, as the specific causes of intrinsic attenuation are modeled phenomenologically, these data will provide an opportunity to conduct process-based studies. The data will also be archived at the IRIS Data Management Center upon completion of the fieldwork.