Between Seismic Speed and Glacial Pace: Cryoseismic Observation of Intermediate-Scale Processes at Lemon Creek Glacier, Alaska

Citation

Labedz, Celeste Ritter (2022) Between Seismic Speed and Glacial Pace: Cryoseismic Observation of Intermediate-Scale Processes at Lemon Creek Glacier, Alaska. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/4y62-sd53. https://resolver.caltech.edu/CaltechTHESIS:06012022-151808806

Abstract

In this thesis, I present three studies in environmental seismology. First, I present an analysis of seismic tremor generated from subglacial water flow during the rapid drainage of an ice-marginal supraglacial lake, collected by an on-ice nodal seismic array. I find that seismic tremor indicates a partial pressurization of the subglacial hydrologic system that was not accompanied by the expected change in glacier surface velocity, suggesting that factors like glacier geometry play a significant role in whether pressurization necessarily leads to velocity change. Using seismometers in this way allows remote observation of active subglacial hydrologic systems as they vary over space and time, a vital parameter for understanding how liquid water affects glacier motion, melting, fracture, and hazards. Second, I present observations of glacier surface crevasse development over space and time, as detected by a dense array of seismometers atop the glacier. I find that icequakes associated with surface crevassing have a magnitude distribution that is swarm-like, rather than aftershock-like, and that the spatiotemporal distribution of events indicates that crevasses regularly widen, deepen, reactivate, and trigger activity at nearby crevasses through cryoseismicity. Understanding surface crevassing activity is valuable for constraining the degree to which glacier surface velocity measurements represent ice flow as a whole, and for interpreting how glacier flow responds to changes in forcing over time. Third, I present an investigation of changes in anthropogenic urban seismic noise in Los Angeles associated with changes in community behavior. I find that changes in human activity from the scale of hours to the scale of months create distinguishable differences in ambient seismic noise power that correlate well with other measures of community behavior. Characterizing anthropogenic seismic noise is beneficial for accurately interpreting measurements of transient seismic wave data collected in urban areas toward goals such as hazard mapping.

Thesis Files