Melt-Triggered Seismic Response in Hydraulically-Active Polar Ice: Observations and Methods

• Main Author: Carmichael, Joshua D.
• Other Authors: Joughin, Ian R
• Format: Thesis
• Language: English
• Published: 2013
• Subjects: Glacial hydraulics; Glaciology; Icequakes; Seismic Monitoring; Signal Detection; Statistical Signal Processing; Geophysics; Electrical engineering; Statistics; earth and space sciences; Taylor Glacier
• Online Access: http://hdl.handle.net/1773/25007

Thesis (Ph.D.)--University of Washington, 2013 Glacier ice responds to environmental forcing through changes in its sliding speed and mass balance. While these changes often occur on daily time scales or longer, they are initiated by brittle deformation events that establish hydrological pathways in hours or seconds and allow meltwater access to englacial or subglacial depths to facilitate ice motion. In this thesis, we (various contributing authors including myself) use seismic monitoring to detect and locate the creation and growth of some of these hydraulic pathways by monitoring their seismic emissions, or icequakes. More specifically, we address (1) what seismic observables, unavailable from other sensing methods, indicate an initial glaciogenic response to melt- water input and (2) if these comprise evidence of feedbacks that may destabilize polar ice under a warming climate. Supplemental to our scientific contributions, we advance statistical processing methods that demonstrably improve the capability of digital detectors at discriminating icequakes from astationary noise. We begin by interpreting geophysical observations collected from a dry-based, sub-freezing (-17 o C), polar glacier environment (Taylor Glacier, ANT). By implementing a calibrated surface energy balance model, we estimate the timing and volume of surface meltwater generated during the collection of seismic data from a six-receiver geophone network. This comparison illustrated that any effectively nonzero meltwater triggered large, repeating icequakes localized near a deep, supraglacial-to-subglacial crack within a melt-water catchment region. The focal mechanisms of these icequakes are consistent with an expansive growth within the crack. Their occurrence at night suggests that this expansion was accommodated by volumetric straining of confined, re-freezing meltwater. These cracks likely sustained their surface-to-bed hydrological connection, in the absence of melt-assisted basal sliding. Further, this appears to be the first report ...