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Published April 16, 2004 | Supplemental Material + Published
Journal Article Open

Geologic context of geodetic data across a Basin and Range normal fault, Crescent Valley, Nevada


Geodetic strain and late Quaternary faulting in the Basin and Range province is distributed over a region much wider than historic seismicity, which is localized near the margins of the province. In the relatively aseismic interior, both the magnitude and direction of geodetic strain may be inconsistent with the Holocene faulting record. We document the best example of such a disagreement across the NE striking, ~55° NW dipping Crescent normal fault, where a NW oriented, 70 km geodetic baseline records contemporary shortening of ~2 mm/yr orthogonal to the fault trace. In contrast, our geomorphic, paleoseismic, and geochronologic analyses of the Crescent fault suggest that a large extensional rupture occurred during the late Holocene epoch. An excavation across the fault at Fourmile Canyon reveals that the most recent event occurred at 2.8 ± 0.1 ka, with net vertical tectonic displacement of 4.6 ± 0.4 m at this location, corresponding to the release of ~3 m of accumulated NW-SE extension. Measured alluvial scarp profiles suggest a minimum rupture length of 30 km along the range front for the event, implying a moment magnitude M_w of at least 6.6. No prior event occurred between ~2.8 ka and ~6.4 ± 0.1 ka, the ^(14)C calender age of strata near the base of the exposed section. Assuming typical slip rates for Basin and Range faults (~0.3 mm/yr), these results imply that up to one third, or ~1 m, of the extensional strain released in the previous earthquake could have reaccumulated across the fault since ~2.8 ka. However, the contemporary shortening implies that the fault is unloading due to a transient process, whose duration is limited to between 6 years (geodetic recording time) and 2.8 ka (the age of the most recent event). These results emphasize the importance of providing accurate geologic data on the timescale of the earthquake cycle in order to evaluate geodetic measurements.

Additional Information

© 2004 American Geophysical Union. Received 31 March 2003; revised 16 October 2003; accepted 18 November 2003; published 16 April 2004. This study was supported by NSF grants EAR 99-03366 and EAR-00-01209 awarded to B. Wernicke and K. Sieh, and grant EAR-9902968 awarded to J. Lee. A. Friedrich acknowledges additional financial support from the University of Potsdam. We thank M. Jackson and R. Bruhn for providing surveying equipment, and B. Phillibosian, R. Heermance, and J. Liu for valuable assistance in the field. We benefited from reviews by D. Hindle, S. Mc Gill, and R. Hetzel and discussions with J. Bell, J. Caskey, C. DePolo, K. Haller, M. Machette, A. Ramelli, and S. Wesnousky on Basin and Range paleoseismology. Auxiliary material for this article contains excavation logs, fault scarp measurements along the Cortez range front, and stratigraphic descriptions of unit exposed in the excavation on the north side of Fourmile Canyon.

Attached Files

Published - friedrich_tectonics2004.pdf

Supplemental Material - 2003TC001528-README.txt

Supplemental Material - 2003TC001528-Supp1.eps

Supplemental Material - 2003TC001528-Supp2.eps

Supplemental Material - 2003TC001528-Supp3.eps

Supplemental Material - 2003TC001528-Supp4.ps


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