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- Some engineering geologic effects of the 1964 Alaska earthquake
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Some engineering geologic effects of the 1964 Alaska earthquake
Abstract
One of the greatest earthquakes of our time rocked southern Alaska on 28 March 1964 at 03.36 GMT. Its magnitude (M 8.3-8.6), duration (3-4 minutes), and extent (about 120 000 km2) would have caused catastrophic damage in a region more heavily populated than Alaska. As it was, 130 lives were lost, and property damages exceeded $311 million.
So great an event holds unusual interest for engineering geologists, who are especially concerned about the effects of natural happenings on the works of man and of steps that can be taken to avert such effects in the future. Heavy damages throughout the meizoseismal zone were caused by direct vibration, ground breakage, subaerial and submarine landsliding, avalanching, ground compaction, tectonic subsidence and uplift, soil liquifaction, and seismic sea waves.
Anchorage, Alaska's largest city, sustained the most damage in absolute terms, although several small coastal communities were completely destroyed by sea waves. At Anchorage, damage was caused chiefly by landsliding and vibration. Much of the city rests on the Bootlegger Cove Clay, an estuarine-marine formation, that contains silty clays of low strength and high sensitivity. Dynamic failure of these clays and of interbedded sand layers led to large-scale landsliding in several parts of the city. Most of the destructive landslides moved primarily by translation, despite wide variations in size, appearance, and complexity. They slid on nearly horizontal slip surfaces in a zone of low shear strength.