DEFORMATION

Crustal deformation, including both vertical and horizontal movement, associated with this earthquake was more extensive than any other related to a single tectonic event. Vertical; movements occurred over a region that basically parallels the continental margin for almost 600 miles. In addition, crustal warping appears to extend inland from the Alaskan Ranger to the Aleutian Trench.

Photo Courtesy of California Geology, November 1971

Observable tectonic deformation included 1.) regional crustal warping, including both uplift and subsidence relative to sea level, 2.) regional horizontal extension and shortening, 3.) displacements along longitudinal reverse faults on land and the sea floor. Comparison of the pre- and post-earthquake displacements came from either tide gage readings, the position of growth limit of certain organisms relative to sea level, the differences in elevation of vegetation relative to the sea level, differences in beach heights, changes in the position of shorelines or differences in tidal bench marks relative to sea level. Vertical uplift averaged 6 feet in height along the Alaskan coast and reached a height of nearly 38 feet on Montague Island. Reverse faults displaced blocks nearly 26 feet in height. To the North and Northwest of the zone of uplift, subsidence that ranged from 1 1/2 feet to 7 1/2 feet dominated the area. Surprisingly, with all this deformation, faults on land were discovered at only two localities, both being reverse type faults. Vertical displacements both upward and downward caused extreme changes in shoreline morphology and widespread destruction of some flora and fauna of the area. Eyewitnesses timed the event using their wristwatches and gave varying accounts of between 1 1/2 and 7 minutes long. Most of the timings ranged from 3 to 4 minutes. The Great San Francisco earthquake of 1906 is said to have lasted only 1 minute.