Both quakes were centered along the Denali Fault.Īndrew Ford, a researcher at the University of Utah, was studying the fault system in southeast Alaska with colleagues Rick Forster and Ron Bruhn, both professors at the University of Utah. Now considered a foreshock of the larger quake, the October earthquake caused no surface ruptures. The November 3 Denali Fault earthquake was preceded by the magnitude 6.7 Nenana Mountain earthquake on October 23. Because the earthquake released most of its energy on the sparsely populated eastern end of the fault, Alaska’s major cities were spared serious damage. The resulting surface rupture was approximately 336 kilometers (209 miles) long, and it cut through streams, divided forests, opened chasms in roads, and even generated fault traces visible across several glaciers. Originating on the previously unknown Susitna Glacier Fault, the earthquake shot eastward along the well-known Denali Fault at a speed of over 11,265 kilometers (7,000 miles) per hour before branching southeast onto the Totschunda Fault. The Denali and Totschunda Faults are located along the northeastern edge of the Wrangell Subplate. The Yakutat block (labeled YAK) prevents the Pacific Plate from subducting smoothly, causing the Wrangell Subplate to break off the North American Plate and rotate counterclockwise. The Pacific Plate is actively subducting (sliding under) the North American Plate at a rate of about 2 inches per year. The map above shows the tectonic plates that influence Alaska’s southeastern fault systems.
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