May 17, 2009

Get your quake on

Since downgraded to a 4.7. Screengrab from Recent Earthquakes in California and Nevada, via the SCEDC. Click to embiggen.

"Employees of a Starbucks located at Hawthorne and Artesia Boulevards work to clean up broken glass that shattered on the floor and reportedly injured one person who was taken to a nearby hospital." Photo by Jay Clendenin for the Los Angeles Times.

This puppy was felt from Arizona to Baja: check out the shakemaps. Where I live the quake was so mild that if I'd been walking around I wouldn't have felt it. The gentle rolling here actually went on for a surprisingly long time, though, maybe 12 seconds or a bit more: a clue for us earthquake geeks that this quake was bigger somewhere.

No sooner had the rolling stopped than the phone rang. My most excellent cousin from Orange County wanted to know whether I'd felt the earthquake.

And here is the cool thing: she and her family had felt the quake a full minute before, and it was much stronger. More clues! It's all about the seismic waves, people. You can read about P waves and S waves and those scary Love waves here, and play with wave frequency and amplitude here.

From the LA Times:
An initial assessment by the Los Angeles Fire Department found "no major structural damage, no serious injuries," according to spokesman Brian Humphrey's Twitter feed. [Twitter feed, OMG. I am now following LAFD on Twitter.]

At the Los Angeles County Sheriff's Lennox station, deputies said the shaking was brief but intense. "It was pretty strong but over in about 10 seconds," said Lt. Kent Wegener. [Wegener...! Father of plate tectonics! This is just scary.]
The earthquake was "a bit deep," said U.S. Geological Survey seismologist Susan Hough – originating 8.4 miles below the surface. "That tends to make it less sharp – less of a jerky, abrupt motion," Hough said. As a result, most of the region felt the quake largely as a rolling motion, though some closer to the center felt more of a jolt.

Lucy Jones, seismologist at the U.S. Geological Survey, said the earthquake appears to be consistent with a rupture on the Newport-Inglewood fault. (She said the quake was too small to break the surface, so they can't definitively identify faults.) Jones said this fault isn't typically thought to be capable of a large quake, like the San Andreas Fault. But it was responsible for the 1933 Long Beach earthquake, which measured about 6.3 in magnitude. The Long Beach quake is about as big as seismologists expect from this fault, she said.
Nothing about the quake or its aftershocks looked unusual, she said. "It's a real garden-variety California earthquake so far."
For the record, my dogs stood up when the rolling/shaking started, wandered around for a minute, got a drink, and then all lay down again and went back to sleep. Californians [affectionate eye roll].

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