Cosmogenic Ages for Earthquake Recurrence Intervals and Debris Flow Fan Deposition, Owens Valley, California

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Science  20 Oct 1995:
Vol. 270, Issue 5235, pp. 447-450
DOI: 10.1126/science.270.5235.447


Model exposure ages (beryllium-10, aluminum-26) of boulders on an offset debris flow fan yield an earthquake recurrence interval between 5800 and 8000 10Be:26Al years for a strand of the Owens Valley fault in California, which last ruptured in an earthquake of moment magnitude >7.5 in 1872. Cosmogenic age estimates for this and several nearby fan surfaces flanking the eastern Sierra Nevada are consistent with stratigraphic relations and suggest that these surfaces were abandoned after 1000, 8000, and 21,000 10Be:26Al years ago. The wide scatter and nonconcordance of 10Be:26Al ages on an older fan surface suggest that boulder erosion and lowering of the fan surface there have influenced apparent exposure ages.