Passive Seismic Imaging of Subglacial Conditions on Thwaites Glacier

Subglacial bed-type (bedrock or sediment) is a significant control on fast glacier-motion. Geophysical techniques provide a relatively efficient means to explore variations in bed type. The GHOST project collected a range of geophysical datasets to explore variability in bed type beneath Thwaite glacier including active source seismic and radar measurements. Over the course of two seasons an array of ~ 200 Magseis Fairfield ZLand 3C nodal seismometers were deployed on Thwaites. The primary goal of this array was to record glacier generated seismicity to explore subglacial dynamics via subglacial stick-slip events and ice dynamics via crevasses generated seismicity. We explore the potential use of this seismic array to image bed type using passive source seismic methods. We will present initial results using two complimentary methods. First, we use the receiver function method, which leverages the recording of earthquakes to identify converted waves that are produced by significant material boundaries, such as those that occur at the ice-bed interface or between sediment-bedrock interfaces. Second, we explore the use of ambient-noise seismic-imaging to measure seismic surface waves traveling across the network. We then use these surface-wave measurements to measure phase velocities which can then be used to identify the presence of large sedimentary layers. We will present initial results of spatial variability in sedimentary structure across our study area and how these are related to variations in basal conditions and flow-speed of Thwaites Glacier.  Finally, we  will show how these data can be used to extract information about sediment properties that can be linked interpreted in terms of physical properties that influence ice sheet flow speed such as porosity.