The total amount of motion along a fault can be estimated by offset geologic markers that were once continuous across the fault. There are various pairs of cross-fault markers along the San Andreas fault in southern California that suggest different amounts of offset ranging from 160-240 km. These estimates assume that the markers were offset solely by sliding along the fault. In this paper, Michael H. Darin and Rebecca J. Dorsey reinterpret one pair of offset markers and use a simple geometric model to show that fault block rotation adjacent to the fault can account for a small but significant amount of the apparent offset, thus reducing the amount of sliding required to displace the formerly continuous markers. Their model provides a new estimate of ~200 km of total offset on the San Andreas fault within the Salton Trough region, which is consistent with all other geologic data from various offset markers. This new lower estimate of total slip on the southern San Andreas fault implies that more slip is required on other faults in California and Arizona, in order to satisfy estimates of the total amount of motion between the Pacific and North American plates.
Erosion of the Tsangpo Gorge by megafloods, Eastern Himalaya
Karl A. Lang et al., Dept. of Earth and Space Sciences, and Quaternary Research Center, University of Washington, Box 351310, Seattle, Washington 98195, USA. Published online 22 July 2013, http://dx.doi.org/10.1130/G34693.1.
Karl Lang and colleagues present new detrital zircon U-Pb provenance data from la
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Geological Society of America