Evolution and Strength of Pacific Fracture Zones

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Previous studies have shown that Pacific fracture zones are strong in some locations, sustaining the stresses associated with differential subsidence across a locked fault, while at other locations they show signs of weakness, acting as preferential conduits for volcanism or supporting anomalously low shear stresses. We find that half of all Geosat crossings of central Pacific fracture zones are inconsistent with a flexurally maintained scarp. We test two hypotheses for the origin of such anomalous crossings: (1) anomalous structures formed at the transform fault during times of changes in plate motions, and preserved at “strong” fracture zones; and (2) anomalous structures representing a posttransform response of the fracture zone to subsequent tectonic activity. We find that three-quarters of the anomalous crossings occur over the parts of fracture zones that formed during or immediately subsequent to times of changes in spreading directions. With the exception of several locations overprinted by hot spot volcanism, these same crossings show no obvious correlation with regional tectonic processes. These observations suggest that most anomalous fracture zone topography is inherited from the transform fault and is not a product of subsequent activity, consistent with the hypothesis that fracture zones generally remain strong throughout their lifetimes.

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Journal of Geophysical Research, v. 101, issue B6, p. 13731-13740