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Magnitude 6.0 Quake Hits Northern California, Causing Injuries and Outages
As numerous sources report, an earthquake of magnitude 6.0 struck California early Sunday morning, with an epicenter about 9 miles south of Napa. According to the San Francisco Chronicle's account, Some power lines down in western Contra Costa County, but Bay Area bridges appeared to be fine, according to the California Highway Patrol. There were widespread reports of power outages, gas leaks and flooding in the North Bay, with at least 15,000 Pacific Gas and Electric Co. customers without power in Vallejo, Napa, Rohnert Park, Santa Rosa and Sonoma. Police reminded motorists to stop at darkened intersections. ... In Benicia, several miles from the epicenter, the quake was strong enough to knock pictures off mantles.
Bay Area bridges appear to have survived the quake -- significant, in that the L.A. Times reports that USGS estimates peg it as "the largest earthquake to strike the Bay Area since the Loma Prieta temblor of 1989," and says that injury reports (especially from glass) are streaming in from the area around Napa. The Times also has a larger estimate of customers suffering power outages: "more than 42,000" around the northern Bay Area. Unsurprisingly, social media channels are full of pictures showing some of the damage.
For those in California, did you feel the quake? (And from how far away?) Update: 08/24 13:15 GMT by T : Also in earthquake news: an even stronger quake (magnitude 6.4) on Saturday struck central Chile, shaking Santiago -- nearly 70 miles from the epicenter -- for more than half a minute, but with "no immediate reports of fatalities or serious damage."
For those in California, did you feel the quake? (And from how far away?) Update: 08/24 13:15 GMT by T : Also in earthquake news: an even stronger quake (magnitude 6.4) on Saturday struck central Chile, shaking Santiago -- nearly 70 miles from the epicenter -- for more than half a minute, but with "no immediate reports of fatalities or serious damage."
Join the Quake catcher network of Stanford. You can order a sensor, but your laptop can detect them too.
http://qcn.stanford.edu/
The detected earthquake
http://qcn.stanford.edu/earthq...
Bert
I am currently working in Santiago and did feel last nights shaking. It is not the first I have felt in the last year but it is definately the strongest. I haven't heard of any problems in Santiago but Valpariso is much closer and a portion of the city was recently damaged in a large fire so this might complicate the recovery efforts there.
I Don't Work Here
Any reports of chemical leaks at area meth refineries?
"Why do Californians think they can "feel" the strength of a quake? It's complete nonsense because you cannot feel its distance."
It's not nonsense at all. Bigger quakes last longer. The duration of the shaking is a good measure of the actual strength, and can be read directly off the seismographs, while more accurate estimates take a while to compute from these and other measurements.
That's why you see initial estimates as "duration magnitude", later revised to "moment magnitude" which more accurately measures the energy from measurements of the distortion of the underground structures due to the stress changes. You'll notice that it's SO good that the adjustment is usually only a couple tenths of a scale point - less than a 2:1 difference in energy.
The rip starts at some point along the fault and propagates along it in fits and starts, much slower than the compression and shear waves from the individual releases, as the motion from the relaxing stresses in the section that let go increases stresses in the next section. This keeps up until the effect reaches a point where the stress isn't enough (at the time) to make it let go. (You get aftershocks when the more gradual readjustments add "straw to the camel's back" and get it going again - or start one on another nearby section or another nearby fault.)
The strength of the wave decays with distance. But the duration increases as the wave takes multiple paths, scattering off underground structure. So a distant earthquake doesn't "feel" shorter than a nearby one. Longer-but-weaker. Also, the P wave propagates much faster than the S wave, is weaker, and doesn't "stretch out in time" much at all. Time separation is greater with distance. They feel very different. (Mnemonic: First the P wave makes you pee, then the S wave ...) So with enough experience one could ballpark both the strength and the distance from the feel of the quake.
For instance: Loma Prieta, a 7.1 moment magnitude (6.9 early duration magnitude estimates), propagated along aobut 22 miles of fault. It lasted 8 seconds, though as you got farther away the shaking got up to 45 seconds before it became too weak to be noticed. I was standing in front of Palo Alto City Hall when it got there, and my perception was first (P wave) "a truck is going over this overpass - wait', I'm not ON an overpass", then (S wave) "being in an airplane experiencing 15 seconds of mild turbulence." (Most ground-bound constructions {except for mobile and modular homes, which are built to be shipped on highways}, weren't built to withstand "15 seconds of mild turbulence". B-b ) I was listening to a San Francisco radio station: Seconds after the shaking started, the announcers got in two sentences (first about feeling an earthquake (P wave), then that it felt big (start of S wave)) before the transmitter failed (a bit into the S wave) - and the shaking was far from over.
The scale is logarithmic base 10, so a 1 point difference in scale is a 10x difference in energy, and thus time. This makes it EASY to guess the magnitude (if your sense of time doesn't distort to much from the excitement). A 6.1 would be 1/10th the energy of Loma P., so also about 1/10th the time, and Nappa to Oakland is comparable to Loma Prieta to Palo Alto, so call it a second and a half of the strong shaking.
On the other hand, for the first quake I felt after moving to CA I was nearly on top of a small one. (I think it was a high 2.x or a low 3.x.) Very sharp single shock - like a car hitting a concrete building while you're inside - followed by "echoes" as the wave moves on rapidly and EVERY building makes the sound of being hit (followed by a chorus of car alarms - shock sensors were common then). Sensation: Being in an elevator when it hit a misaligned section of the guide track. Three-stage perceptual distortion, as I realized that I was standing on the ground and my brain momentarily remapped my mo
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
The quake was in Napa, which most people don't consider to be the Bay Area. Yes, it's nearby, but it's not really the Bay Area.
When the headlines read "Massive Quake Hits Bay Area!", most people will think of places like San Francisco and Oakland. According to Google Maps, Oakland to Napa County Airport (near the epicenter) is 37 miles and my guess is 30 miles in a straight line.
See that map here: http://www.google.org/publical...
In my part of Oakland, it was big enough to wake me up, but nothing rattled or hit the floor.
Napa got hammered, but the Bay Area just got its dishes rattled.
I saw a bunch of panic on social media this morning, from people out of the area. All they saw was "Bay Area Earthquake" in the media.