Mathematics – Logic
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p31a0964c&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #P31A-0964
Mathematics
Logic
8010 Fractures And Faults, 5475 Tectonics (8149), 6218 Jovian Satellites
Scientific paper
Ganymede, the largest satellite of Jupiter, is transected by numerous fault zones. Galileo images have shown more than five craters cut by these fault zones. Due to their initial near-circular shape, these craters make ideal strain markers for the surface of Ganymede. We have developed two methods for analyzing strained craters. One method is used for craters cut by a fault zone which is narrow with respect to the crater diameter, calculating strain based on the displacement of best-fit centers to intact crater rim segments. The second method, for craters which are pervasively faulted, calculates the strain based on the ellipticity and orientation of the best fit ellipse to intact crater rim segments. While previous planetary studies have examined simple extension based on the elongation of strained craters, our methods are able to calculate the relative roles of both simple extension and simple shear in the fault zones. Our results show that many of the fault zones that morphologically resemble tilt-block normal faults exhibit 50% to 180% extensional strain. Other fault zones which exhibit subdued morphology consistent with narrow graben show more modest extensional strains of 5% to 15%. Two of the craters have well over a kilometer of offset due to simple shear. The crater-based strain measurements allow us to test other strain measurement techniques on Ganymede fault zones. In a region of grooved terrain with Galileo stereo coverage, extensional strain of 50% was estimated based on assumptions about fault geometry from the images. Directly comparing strain measurements from craters to measurements from fault geometry allows us to refine our fault geometry assumptions, with the goal of being able to estimate strain wherever we have high resolution image data for Ganymede. If high extensional strains are indeed common on Ganymede, then the lack of contractional structures on Ganymede becomes more problematic. Understanding the amount of strain represented by fault zones on Ganymede, and their evolution through time, is critical for understanding the underlying driving mechanisms of Ganymede tectonics.
Collins Geoffrey C.
Pappalardo Robert T.
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