Mathematics – Logic
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p21b1599c&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P21B-1599
Mathematics
Logic
[6221] Planetary Sciences: Solar System Objects / Europa
Scientific paper
A detailed kinematic and topographic survey was performed on numerous Europan double ridges to quantify ratios of ridge-orthogonal and ridge-parallel motions and to provide a greater understanding of their morphological characteristics. Double ridges (usually referred to simply as ridges) consist of two raised edifices that flank a central trough. We first explored possible ridge formation mechanisms using a displacement ratio (DR) technique which makes use of relatively older features crosscut by a ridge and associated geometric relationships between the total separation, strike-slip offset, contractional offset, and angle at which that feature is crosscut by that ridge. High-resolution Galileo images (less than ~200 m/pixel) were utilized for this kinematic survey and the DR technique was applied to 13 double ridges with visible offsets. Next, high-resolution (~6-180 m/pixel) combined stereographic (3D) and photoclinometric (PC) images were used to create a total of 210 topographic profiles across 24 near-linear double ridges (7 of which were also included in the kinematic survey). Individual ridge height and width, total ridge width, peak to peak distances, inner and outer slopes, and height to width ratios were calculated to quantify more ridge characteristics than any previous topographic study. A component of shearing was found along every ridge measured using the DR technique. Shearing is oftentimes accompanied by dilation; however, this does not necessitate that dilation forms ridges. We also observed in the kinematic and topographic surveys that post-formation tectonic modification, such as dilation of the medial trough, may have occurred after the ridge edifices formed. In the topographic survey, the majority of slopes measured are less than 20°, suggesting that unconsolidated, granular ice is not the primary component of ridge surfaces (i.e., most slope angles are not consistent with processes involving granular mass wasting). Overall low slopes and low height to width ratios suggest that predominantly time-dependent, viscoplastic gravitational collapse may occur along the slopes of ridges, implying relatively warm ice. Based on the results of the kinematic analyses (i.e., the presence of shearing along each of the 13 ridges examined with our displacement ratio technique) and the detailed topographic survey, shearing (i.e., frictional heating) is a likely source for the localized warming that may provide a mechanism for initial ridge construction and may be a mechanism through which ridge carapaces viscoplastically relax, creating the low slopes observed along these ridges. These two complimentary surveys provide a more thorough characterization of the ridge morphology and kinematic behavior, placing greater constraints on existing ridge formation models.
Coulter C. E.
Kattenhorn Simon A.
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