Lasting nearly five minutes, it was the most powerful recorded earthquake in U.S. and North American history, and the third most powerful ever measured by seismograph. It had a moment magnitude of 9.2 and registered 8.4 on the Richter scale.[1]
“Lasting nearly five minutes, it was the most powerful recorded earthquake in U.S. and North American history, and the third most powerful ever measured by seismograph. It had a moment magnitude of 9.2 and registered 8.4 on the Richter scale.[1]”
http://en.wikipedia.org/wiki/Good_Friday_Earthquake