Lasting 4 minutes and 38 seconds, it was the most powerful recorded earthquake in U.S. and North American history, and the second most powerful ever measured by seismograph. It had a moment magnitude of 9.2, making it the second strongest earthquake in recorded history — the strongest being the 1960 Valdivia earthquake in Chile.

1964 Alaskan Earthquake ( Good Friday Earthquake ) - http://en.wikipedia.org/wiki/1964_Alaska_earthquake

Everyone on Reddit kept saying "Wow, that was long" for the Napa earthquake. It was only 20 seconds long. I guess most are only about 5-10 seconds. I cannot imagine constant shaking for nearly 5 minutes.