Mathematics – Logic
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p31a0960v&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #P31A-0960
Mathematics
Logic
8010 Fractures And Faults, 6218 Jovian Satellites
Scientific paper
Small-scale normal and shear motions (approaching the limits of resolution; < a few 100 m) along lineaments on Europa are not well constrained. Previous work has not differentiated, quantified, and catalogued the small-scale motions along the lengths of lineaments of varying morphologies. In their characterizations, such work principally utilized rigid-block reconstructions which do not address any variations in motion along the lengths of lineaments. Also, these investigations typically did not consider the effect of relatively small amounts of fault-orthogonal motion, or the apparent offsets caused by convergence, if present. For example, the existence of lateral offsets along a lineament does not explicitly require that any strike-slip motion occurred at all as offsets could purely be the result of convergence. Using a technique which utilizes characteristic changes in the distribution of geometric relations of crosscutting features, small-scale motions can be inferred (whether strike-slip or fault-orthogonal), within the limits of image resolution. By measuring the total offset, the separation, and alpha (the clockwise angle between a lineament and a crosscut feature) for every crosscut feature along the length of the lineament (i.e., a range of alpha values), the actual motions can be resolved. Specifically, by using these measured quantities and a series of trigonometric equations, opening, convergence, actual strike-slip, or a combination of strike-slip and opening/convergence can be determined. Actual motions along lineaments become particularly apparent in graphs of alpha versus separation, which display different patterns depending on the displacement ratio (DR: the ratio of opening/convergence to strike-slip), which can be estimated from the graph. The accuracy of this technique is limited to DR < 3. If a crosscut feature is approximately orthogonal to a slipped lineament, the observable strike-slip component of motion would have been unaffected by convergence or opening, allowing the strike-slip offset to be measured precisely. Using this offset, the exact amount of convergence can be determined using the DR evident in the alpha versus separation graph. The true strike-slip offset can be determined very accurately using features that may be several tens of degrees from being orthogonal to a lineament, however, the accuracy decreases as DR increases. This technique can be applied to the analysis of lineaments of any morphologic type. Therefore, unraveling actual motions along lineaments can be used to evaluate likely DR values along Europan lineaments and also to evaluate current conceptual models for the formation of linear features on Europa, such as troughs, ridges, ridge complexes, and bands. Another benefit of this technique is that the distribution of motions along the length of a lineament can be catalogued, which may foster a better understanding of the mechanics of motions along lineaments (e.g., elastic vs. transform).
Kattenhorn Simon A.
Vetter J.
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