Obviously, this is a poor example. It was a magnitude 3.1, so no one felt it, and it was 100 miles north of San Francisco.
The last one anybody felt was on Feb 21st at 11:01 AM, and the first (non-automated) tweet was at 11:21 AM (http://twitter.com/indiaknight/statuses/1234962301). This example is similarly bad, since it didn't really affect anyone in a big way. However, for instant reactions to notable events, Twitter can't be beat. If today's earthquake had been "the big one," you can bet twitter would have been flooded with information, missing people reports, locations for aid, firsthand accounts and so on.
The last one anybody felt was on Feb 21st at 11:01 AM, and the first (non-automated) tweet was at 11:21 AM (http://twitter.com/indiaknight/statuses/1234962301). This example is similarly bad, since it didn't really affect anyone in a big way. However, for instant reactions to notable events, Twitter can't be beat. If today's earthquake had been "the big one," you can bet twitter would have been flooded with information, missing people reports, locations for aid, firsthand accounts and so on.