Scientific Colloquium
November 8, 2013

"Antarctic Rifts as an Analog for Studying Tidal Motions along Cracks on Icy Satellites"

A variety of ridges and dilational bands have been observed on Europa. Double ridges, which are thought to flank a central fracture, are among the most common tectonic features on Europa. While their exact formation mechanism remains a mystery, cyclic motion of the central fracture, induced by tidal stresses, likely plays a role in their development. If regional tension is applied to a fault that is undergoing cyclic tidal motions, other more complex tectonic systems may form. The different observed morphologies of ridges and bands may thus depend on the rate of regional expansion relative to the tidal timescale. Regional expansion that is much faster than the ridge formation timescale would likely produce a smooth dilational band because ridges would not have time to form as the fracture was being pulled apart. Ridged bands, on the other hand, display parallel ridge structures. This type of band may form as a result of expansion that occurred on a timescale commensurate with the ridge formation timescale, allowing new ridge pairs to form throughout the dilation process. Together these three classes of tectonic features may represent a continuum of formation in which ridges and dilational bands are end members. Ross Ice Shelf, Antarctica, represents an Earth analog for the interaction of regional dilation and tidal motion and may provide insight to the model proposed for Europa. Tensile failures near the front of the Ross Ice Shelf exhibit secular dilation, upon which a tidal working of the rift can be observed. From this analog we conclude that the extension model for Europa may be credible and that the secular dilation is driven mainly by a regional source. Wedging of the rift apart by its infill material drives a second source of dilation. We will present an overview on Europa and its observed morphologies. We will also present an overview on Antarctic ice shelves and their potential as an analog for further modeling of icy moons.

About the speakers:

Kelly Brunt joined the Cryospheric Sciences Laboratory as an Assistant Research Scientist in June 2010. She obtained a B.S. in Geology from Syracuse University and an M.S. in Geology from the University of Montana. She received her Ph.D. in Geophysics from the University of Chicago in 2008, modeling ice-shelf flow and the connection between ice shelves, ice streams, and the ocean. As a postdoctoral scholar at Scripps Institution of Oceanography, she worked on the calibration and validation of Ice, Cloud, and land Elevation Satellite (ICESat) laser altimetry data. At Goddard, Dr. Brunt provides support to the ICESat-2 mission, where her current role involves the planning for the post-launch calibration and validation of ICESat-2 data. Additionally, she is working with MABEL, a high-altitude airborne laser altimeter designed as a simulator for ICESat-2. Her research focus is on Antarctic ice shelves, which are sensitive to changes in the state of the ocean and are early indicators of ice-sheet change. She has been using both in situ and remote techniques to investigate these regions. Specifically, she has used ICESat data to examine in detail the dynamics of ice-shelf grounding zones. She has also used MODIS and ASAR data to observe a unique calving event of the Sulzberger Ice Shelf, triggered by the 2011 Japanese earthquake and tsunami. And she has collected GPS data to model the flow of the Ross Ice Shelf. Her work has brought her to the Antarctic on 9 separate occasions.
Terry Hurford joined the Planetary Systems Laboratory as a Research Scientist in September 2008. He obtained a B.S. in Astronomy and Physics from University of Arizona, and received his Ph.D. in Planetary Science from the University of Arizona in 2005. His thesis was titled: Tides and Tidal Stress: Applications for Europa. He served as a NASA Postdoctoral Program fellow in the Geodynamics Laboratory where his focused on the influence of tidal stress on eruptions from Enceladus’ south polar region. At Goddard, Dr. Hurford provides operational support for the Composite Infrared Spectrometer instrument on the Cassini mission, where his current role involves the planning observations of icy satellites of Saturn. His research focus is on the geology and geophysics of icy satellites. He uses theoretical models of tidal stress and spacecraft observations to investigate how icy satellites evolve through tidal processes.
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