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Published March 12, 2009 | Published
Journal Article Open

Kinematic behavior of southern Alaska constrained by westward decreasing postglacial slip rates on the Denali Fault, Alaska


Long-term slip rates for the Denali Fault in southern Alaska are derived using ^(10)Be cosmogenic radionuclide (CRN) dating of offset glacial moraines at two sites. Correction of ^(10)Be CRN model ages for the effect of snow shielding uses historical, regional snow cover data scaled to the site altitudes. To integrate the time variation of snow cover, we included the relative changes in effective wetness over the last 11 ka, derived from lake-level records and δ^(18)O variations from Alaskan lakes. The moraine CRN model ages are normally distributed around an average of 12.1 ± 1.0 ka (n = 22, ± 1σ). The slip rate decreases westward from ~13 mm/a at 144°49′W to about 7 mm/a at 149°26′W. The data are consistent with a kinematic model in which southern Alaska translates northwestward at a rate of ~14 mm/a relative to a stable northern Alaska with no rotation. This suggests progressive slip partitioning between the Denali Fault and the active fold and thrust belt at the northern front of the Alaska range, with convergence rates increasing westward from ~4 mm/a to 11 mm/a between ~149°W and 145°W. As the two moraines sampled for this study were emplaced synchronously, our suggestion of a westward decrease in the slip rate of the Denali Fault relies largely upon the measured offsets at both sites, regardless of any potential systematic uncertainty in the CRN model ages.

Additional Information

© 2009 American Geophysical Union. Received 16 March 2007; accepted 9 December 2008; published 12 March 2009. The sample processing and dating work was performed under the auspices of the U.S. Department of Energy, at the University of California Lawrence Livermore National Laboratory, under contract W-7405-Eng-48 and under the sponsorship of the Laboratory Directed Research and Development program (UCRL-JRNL-228719). Field work was supported by the Gordon and Betty Moore Foundation, through the Tectonics Observatory at Caltech, and by grant NAG5–10406 from NASA to KS. This work was also supported by NSF research grant EAR-0107114 to CMR. We are grateful to John Galetzka, Ana Cadena, and Keegan Fengler for their help with the total station measurements. We thank J. Gosse and an anonymous reviewer for their thoughtful reviews together with the associate editor Gideon Rosenbaum for his comments. This is University of California UCRL- JRNL-228719 and Tectonics Observatory contribution 98.

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