Determining formation mechanisms of ridges on Jupiter's icy moon, Europa

Europa is Jupiter's fourth largest moon and has been imaged by both NASA's Voyager and Galileo spacecraft. The icy shell of this moon has been crosscut by several different types of lineaments throughout its geologic history. Ridges are the most ubiquitous lineaments on Europa's surface, many of which have apparent offsets and so appear to be strike-slip faults. Recent formation models have proposed ridges may be created through shearing mechanisms, although previous models characterized them as tension fractures. A quantitative analysis has been performed to determine the dominant deformation characteristics along ridges and thus resolve the factors that contributed to their development. Several crosscutting ridges in two high-resolution Galileo images in Europa's southern hemisphere show apparent lateral offsets. ISIS software was used to reproject images into a transverse mercator projection to best conserve line lengths and to preserve angular relationships between ridges and the features they crosscut. The preservation of angular relationships is important to accurately differentiate and constrain shearing-related offsets from convergence-related offsets, using a technique developed at the University of Idaho (Vetter, 2005, MS thesis). The two displacement components were used to calculate the shearing-to-contraction ratio along each ridge. This quantitative analysis of the offsets across ridge-like strike-slip faults clarifies ridge formation mechanisms (often involving a combination of contraction and shearing), allowing current ridge formation models to be refined and providing better insights into how Europa's ice shell deforms in response to tidal stresses.

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