Rocking and Rolling in the Bay Area
About an hour and a half ago, we had a fairly small earthquake here in the San Francisco Bay Area.
While it only had a magnitude of 4.0, it was interesting to see the reaction on various social networks such as Facebook and Twitter. In fact, when I first felt our building shake, I wasn’t sure if there had actually been an earthquake, so I checked my Twitter account.
Only a few minutes later, this is what my feed looked like.
And here is the shake map for the earthquake:

According to the USGS, it was centered on an unnamed fault located near the Calaveras Fault:
A light earthquake centered near Alamo shook the Bay Area Friday evening. Reported at 9 p.m., it was a magnitude 4.0, said the U.S. Geological Survey.
The Contra Costa and Alameda County sheriff’s offices said they had no reports of damage.
The quake was felt in Petaluma to the north and in Gilroy and Turlock to the south and southeast, said David Oppenheimer, a seismologist with the geological survey. He said it occurred on an unnamed fault about 2.5 miles from the larger Calaveras fault and two miles north-northeast of Alamo, on Serafix Road.
A cluster of quakes occurred on the same fault in April 1990, with 18 registering at 3.0 or higher in a three-week period, Oppenheimer said. He said the larger quakes in that sequence caused minor structural damage to nearby homes.
Friday’s earthquake took place about 10 miles underground, more than twice as deep as the 1990 quakes, and thus is probably less likely to be part of a cluster or cause damage, Oppenheimer said.
Bummer, I predicted that it was actually on the Calaveras Fault itself.
Anyway, not really a big deal in the end. But the fusion of social media and science is always interesting. We’ve written about Twitter before as well, also in terms of earthquakes and disseminating information.
Similar Posts on Geology News:
- M7.8 Earthquake in Central China
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- Earthquakes Can Cause Remote Events Worldwide
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- San Andreas Fault Observatory at Depth



My girlfriend (also a geologist) and I had just returned from going out to dinner, sat down to watch a movie and then we both shouted “Earthquake!” at the same time. Of course we then went on to Did You Feel It and were the first to report in our zip code. Nerds!
Hah, nice! Yeah. My roommates were not home, so I had no one to geek out to. Though I wasn’t really sure if I felt it at first. So I used Twitter to confirm. That actually gives me some relief though, since I live near the top of a 20 story building in San Francisco. Hopefully this thing is built pretty solidly. ;)