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Crustal structure of the Alaska Range orogen and Denali fault along the Richardson Highway

By
Michael A. Fisher
Michael A. Fisher
1
U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, California 94025, USA
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Louise Pellerin
Louise Pellerin
2
Green Engineering, Inc., 2215 Curtis St., Berkeley, California 94702, USA
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Warren J. Nokleberg
Warren J. Nokleberg
3
U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, California 94025, USA
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Natalia A. Ratchkovski
Natalia A. Ratchkovski
4
Geophysical Institute, University of Alaska, P.O. Box 757320, Fairbanks, Alaska 99775, USA
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Jonathan M.G. Glen
Jonathan M.G. Glen
5
U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, California 94025, USA
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Published:
January 01, 2007

A suite of geophysical data obtained along the Richardson Highway crosses the eastern Alaska Range and Denali fault and reveals the crustal structure of the orogen. Strong seismic reflections from within the orogen north of the Denali fault dip as steeply as 25° north and extend downward to depths between 20 and 25 km. These reflections reveal what is probably a shear zone that transects most of the crust and is part of a crustal-scale duplex structure that probably formed during the Late Cretaceous. These structures, however, appear to be relict because over the past 20 years, they have produced little or no seismicity despite the nearby Mw = 7.9 Denali fault earthquake that struck in 2002. The Denali fault is nonreflective, but we interpret modeled magnetotelluric (MT), gravity, and magnetic data to propose that the fault dips steeply to vertically. Modeling of MT data shows that aftershocks of the 2002 Denali fault earthquake occurred above a rock body that has low electrical resistivity (>10 ohm-m), which might signify the presence of fluids in the middle and lower crust.

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GSA Special Papers

Tectonic Growth of a Collisional Continental Margin: Crustal Evolution of Southern Alaska

Kenneth D. Ridgway
Kenneth D. Ridgway
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Jeffrey M. Trop
Jeffrey M. Trop
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Jonathan M.G. Glen
Jonathan M.G. Glen
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J. Michael O'Neill
J. Michael O'Neill
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Geological Society of America
Volume
431
ISBN print:
9780813724317
Publication date:
January 01, 2007

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