|AAPT Winter Meeting 2006|
The 1964 earthquake occurred at 5:36 PM on March 27, 1964. There were 4 minutes of ground motion. The magnitude was 9.2, and it affected 100,000 square miles. Earth movement ranged from 10 m upward to 2 m downwards. 137 people were killed. Landslides occurred in downtown Anchorage. There was a subsidence of 3 m along 4th Avenue. Anchorage sits on the Bootlegger Cove formation, which is a layer of gravel over a layer of weak, thixotropic clay. The clay failed and slid during the earthquake.
We cannot avoid "big" earthquakes by relieving pressure with "little" earthquakes. We would need one every six minutes for 600 years. Earthquakes are a result of plate tectonics. As plates move against each other, pressures build up, which are released suddenly, resulting in earthquakes.
During the 1964 earthquake, 120 of the 137 deaths were caused by tsunamis. A tsunami is a series of waves with a long wavelength and period. The period can be minutes to hours, while the wavelength can be on the order of 100 km. A tsunami is generated by the sudden displacement of sea water. This usually occurs at subduction zones. A tsunami can also be generated by a landslide. In 1958 the Lituya bay slide generated a tsnami that rose water levels up to 1720' ASL. A tsunami can also be generated by meteor or comet impact. The speed of travel depends on the depth of the water according to the equation v=sqrt(gd). In deep water, a typical speed is 500 mph.