How long did the shaking last?

"At almost precisely 5:12 a.m. local time, a foreshock occurred with sufficient force to be felt widely throughout the San Francisco Bay area. The great earthquake broke loose some 20 to 25 seconds later, with an epicenter near San Francisco... Violent shocks punctuated the strong shaking, which lasted some 45 to 60 seconds. The earthquake was felt from southern Oregon to south of Los Angeles and inland as far as central Nevada." Bill Ellsworth
Hotel St. Francis northwest corner of Powell and Geary streets.

Hotel St. Francis northwest corner of Powell and Geary streets. Looking southwest from Post and Stockton streets. (Image from the Steinbrugge Collection of the UC Berkeley Earthquake Engineering Research Center)