Ambient and teleseismic elastic wavefields of the Ross Ice Shelf, Antarctica, and their application to crustal scale seismic imaging
Date
2020
Authors
Baker, Michael G., author
Aster, Richard C., advisor
Schutt, Derek L., committee member
Krueger, David A., committee member
Dueker, Ken G., committee member
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Abstract
Laterally extensive floating tabular ice, such as the Ross Ice Shelf in Antarctica, is mechanically equivalent to a floating elastic plate and thus supports a variety of vibrational modes, including short-period (< 20 s) elastic waves, intermediate-to-long period (20–100 s) buoyancy-coupled elastic plate waves, and ultra long period (>100 s) gravity waves. Vibrational energy may be excited by near-field sources such as intra-shelf crevassing or the impingement of ocean gravity waves at the shelf ice front, and also by far-field sources such as teleseismic earthquake waves incident at the sub-shelf seafloor and the shelf grounded margins. Broadband seismometers deployed on an ice shelf readily observe these signals and facilitate large scale studies of ice shelf properties (via, e.g., travel-time tomography or velocity dispersion analysis) and near-field environment processes (via remote signal detection and analysis). Using two years of continuous data from a 34-station broadband seismic array deployed to the Ross Ice Shelf, Antarctica, I analyzed spatial and temporal variations in the short-to-intermediate period (0.4–25 s) ambient and teleseismic vibrational wavefields. I show that the ambient, ocean-wave-coupled wavefields are strongly modulated by sea ice concentrations in the adjacent Ross Sea, and identify three separate source processes operating in distinct period bands. Next, I show that body wave and surface wave arrivals from teleseismic earthquakes (>3000 km distant) are observed on the vertical components of ice shelf-sited seismometers with signal-to-noise ratios generally sufficient for crustal and mantle scale tomographic studies. I also show that teleseismic S-waves incident at the grounded margins routinely generate symmetric mode Lamb waves which propagate a minimum of 250 km into the ice shelf interior; this phenomenon occurs throughout the year, with broad azimuthal distribution, and may be exploited for travel-time tomography of the ice shelf. Finally, I present an algorithm for processing vertical channel autocorrelations of teleseismic P-wave coda, as recorded by floating-ice-sited seismometers, to illuminate crustal-scale features such as the Mohorovičić discontinuity. I present Markov Chain Monte Carlo inversions of these autocorrelations which yield crustal thickness estimates that are compatible with previous studies of crustal thicknesses for the Ross Sea Embayment and West Antarctica.
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Subject
environmental seismology
seismology
ice shelves
cyroseismology