WHY DO EARTHQUAKES OCCUR IN SOUTHERN ALASKA?
Earthquakes are commonplace throughout much of Alaska. On average there is a magnitude 7 or greater earthquake somewhere in or offshore Alaska every 1 to 2 years and a magnitude 8 or greater quake about every 13 years. These quakes occur as a result of stresses caused by movements of tectonic plates that make up the Earth’s outer shell. In this region, the Pacific Plate moves steadily northward at a rate of about 2 inches per year and descends, or “subducts,” beneath the North American Plate. An irregularity on top of the Pacific Plate, known as the Yakutat block (YAK), impedes smooth subduction of the Pacific Plate and has caused a wedged-shaped piece of the North American Plate, the Wrangell Subplate, to break loose and rotate counterclockwise. The western Alaska Range, which includes Mount McKinley, the highest peak in North America, is a zone of compression between the North American Plate and the Wrangell Subplate. The Denali and Totschunda Faults form the northeastern margin of t
