Other
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p53b1243b&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P53B-1243
Other
5475 Tectonics (8149), 6221 Europa
Scientific paper
Europa, Jupiter's fourth largest moon, has been imaged by both NASA's Voyager and Galileo spacecraft. The most common lineaments found on Europa's pervasively fractured surface are ridges, many of which also appear to be strike-slip faults in that they offset other crosscutting lineaments. Recent formation models have proposed that ridges may be created through shearing, although earlier models characterized them as tension fractures. We developed a technique to determine the dominant deformation characteristics along ridges having apparent lateral offsets. We show evidence for both lateral shearing and convergence along ridges, indicating that apparent lateral offsets are not purely the result of strike-slip motions. Using ISIS software, Galileo images were reprojected using both orthogonal and transverse mercator projections, to conserve line lengths and preserve angular relationships, respectively. These projections are needed to accurately differentiate shearing-related offsets from convergence-related offsets. However, there are caveats to our developed technique for determining these relative offsets and thus the formation mechanisms behind ridge development. Apparent offsets must be large enough to overcome image resolution constraints. It is also important that several offset lineaments crosscut the ridge with a wide range of orientations relative to the ridge in order to most accurately determine the relative motions across the ridge. Relative orientations are defined by angle alpha, measured clockwise from the ridge to the crosscut feature. At both small and large alpha angles (0 to 30 degrees and 160 to 180 degrees), apparent offsets due to convergence across the ridge may become relatively large compared to where alpha angles are closer to 90 degrees (for which pure ridge-orthogonal motion gives an apparent offset of zero). Causes of apparent offsets are quantified using plots of normalized separations of offset features versus alpha, which produce unique curves depending on the relative amounts of lateral motion and convergence. This analysis of offsets across ridges that resemble strike-slip faults will highlight the processes that drive ridge development (i.e., dilation, contraction, lateral shearing, or a combination thereof) and current ridge formation models may ultimately be refined.
Bader C.
Kattenhorn Simon A.
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