What happened
On the evening of 27 March 1964, local time, the subduction zone beneath Prince William Sound ruptured. The shaking lasted about four and a half minutes. Whole neighbourhoods of Anchorage slumped, and at Valdez and Seward underwater landslides set off local tsunamis. Tsunami waves reached as far as California and Oregon. About 130 people died – most of them in the tsunamis. Studies of this earthquake helped confirm plate tectonics and the mechanism of great subduction-zone earthquakes.
How to read these data
Magnitude measures the energy released at the focus: each step is about 32 times more energy, so an M 9 earthquake releases about a thousand times more energy than an M 7. Its effects, however, also depend on focal depth, distance to cities, ground conditions and building quality – a shallow M 7 beneath a city can be deadlier than a deep M 8 under the ocean.
Data: USGS ComCat (official19640328033616_30) · Wikipedia (pl) · Wikipedia (en)