Web Extra  Tuesday, May 14

A moderate earthquake of magnitude-5.2 struck 80 miles southeast of San Francisco Monday night. No injuries and little damage occurred. Geotimes contributing writer Naomi Lubick was at home on the scene:

California Quake: Just a reminder…

At about 10 p.m. last night, I was sitting at my computer when I had the sensation that the room was swaying. I was pretty tired, so I ignored it at first. Then the tabletop started to move, and I immediately scrambled underneath the table onto all fours.
I crouched for several seconds, trembling, with a stream of images moving through my head of my apartment's roof caving in and of earthquake drills. Should I run to the doorway? Is that vase on top of my bookshelf about to topple over?

And then it was over.

The U.S. Geological Survey reported a magnitude-5.2 earthquake, lasting about 5 seconds, at 10:00:29 p.m. Pacific Time, centered 3 miles southwest of Gilroy, Calif., and almost 5 miles down into Earth's crust. I looked it up immediately online, as soon as I could sit down in my chair again and breathe normally. The television news reported it about 5 minutes later, and several friends called to say, hey, did you feel that?

This quake was too small to have a large effect in a region so well prepared for seismic events. The ShakeMap that the U.S. Geologic Survey (USGS) posts online said that it felt like a "light" earthquake in San Francisco. (When I checked the map the next morning, almost 12,000 people had reported what it felt like to them.) By about 10:15 p.m., the USGS had all the information posted. The chances of this one being a precursor - it did happen within the San Andreas fault zone, which is worrisome for those of us expecting "The Big One" - were small, about 10 percent, according to the page I found. More likely there would be smaller aftershocks. The profile of the quake, taken by seismometers around the Bay Area, at places like the University of California at Berkeley and the USGS in Palo Alto, was posted almost immediately.

Our seismic tracking system is almost as quick as an earthquake itself, or a lightning strike. The speed with which the news had reported it and we had all returned to normal is astonishing to me. But my physical reaction to the event indicated something big had happened. By 10:30, I was back at my computer working - but my breathing/heartbeat didn't return to normal until much later.

Naomi Lubick
Geotimes contributing writer

Related Links:

U.S. Geological Survey ShakeMap for the 5.2-Magnitude Gilroy quake

USGS Preliminary Earthquake Report

Focal mechanism with stress diagram

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