What was the Richter scale magnitude of the Great Alaska Earthquake in March, 1964?

With no warning on a spring day under the waters of the Pacific Ocean, a large rupture occurred in the crust of the Earth. The date was 27 March 1964. The magnitude was estimated over and over and only in the past couple of decades have scientists been able to compare the magnitude of the original event with properly calibrated instruments. For several decades the estimate was between 8.4 and 8.6, but later checks showed that the seismometers of the day were simply not able to correctly record such a large magnitude. The settled magnitude is a daunting 9.2 which is enormous.

Recall from your mathematics that a logarithmic scale number like the Richter Scale allows that an increase of one unit means that the magnitude is ten times different. So a 4.0 is ten times weaker than a 5.0 and a hundred times weaker than a 6.0. To date the 1964 Great Alaska Earthquake is the second largest on record. Due to the time of day and the sparse population, the death count was minimal, with more deaths attributed to tsunamis than to the shaking itself. The initial event lasted for over 5 minutes.

Evidence of the event is still visible in many parts of coastal south-central Alaska. Monuments to deaths in Washington, Oregon, California, and Hawai'i speak of the fierceness of the tsunami generated by the earthquake.