A fairly significant earthquake hit the northern San Francisco bay area this morning (Aug 24, 2014). It occurred about 3:20 AM local time, had a magnitude of 6.0 and was centered in the American canyon area SW of Napa Ca. I live in the south SF bay area, closer to San Jose, perhaps 50 miles away. The earthquake woke me up and I distinctly felt the earth moving. I estimated it at about a magnitude 4 from how it felt where I was. I didn't hear anything crashing to the floor or anything, so I rolled over and went back to sleep. But I was curious and turned on the local news when I woke up to see if they had any comment on it. Turns out it wasn't a small earthquake at all, but a bigger earthquake some distance away. The local TV stations are all doing wall-to-wall 'breaking-news' coverage. Early reports of these things are often exaggerated. (TV news shows the pictures of the worst damage over and over, without making clear how scattered it is.) But reports are that there's widespread minor damage in the north bay, mostly stuff dumpted off shelves and superficial wall cracking. There's reports of scattered serious structural damage as well, mostly older structures. Apparently Napa's old stone library has significant damage (it has been retrofitted). And one of the oldest buildings in town, currently a wine-tasting center for local wineries, was reportedly wrecked. Luckily the quake happened in the middle of the night and nobody was in these buildings. TV is showing photos of buildings that lost parts of their brick facades. Worst damage was in a mobile home park (isn't it always) where a large fire broke out and arriving firemen discovered no water pressure due to broken lines. Lots of power outages, but it seems to be spotty. Major roads in the area seem to be open and flowing pretty well. There are photos of a few badly cracked and buckled roads, probably from earth-slippage beneath, but they seem to mostly be smaller streets and roads, not big numbered highways. There's an Indy-car race scheduled in adjoining Sonoma county that's expected to draw big crowds that's still on. Reports of about 70 injuries, but local hospitals report none are life threatening. (The worst reported at Napa's county's main trauma center was a broken hip.) It was felt over a wide area, ranging from San Jose in the south to Sacramento to the northeast. But damage seems to concentrated in a much smaller area closer to the center. All in all, it could have been worse. This wasn't close to being the expected 'big-one', it was just a reminder. Here's the USGS incident report: http://earthquake.usgs.gov/earthquakes/eventpage/nc72282711#summary
Napa press conference just completed. City officials report several street closures downtown due to things ranging from broken glass to buildings whose structural integrity is questionable. Local lumberyards are donating lumber to board up windows. Teams being sent out to inspect damaged buildings to decide whether to red-tag them. That being said, the police chief said many streets have little damage, aren't closed, and he urged visitors that have reservations at restaurants and whatever to call ahead and that it's fine with the police to show up if the business is going to be open. New reports of three critical injuries, including a child hit by bricks from a collapsed chimney and helicoptered to a neurosurgery center. Dozens of water-main breaks and leaks. Public works is working to locate and isolate them and to shut off necessary lines. PGE (the local utility) is busily checking out reports of gas leaks. Unknown how many of them there really are. A shelter is being set up at a local high-school. Local urban search-and-rescue teams being sent in as a precaution, but no reports of any missing people at this time. Major airports in the SF bay area are all working normally. The control tower at Napa airport (a general-aviation airport) is closed due to possible structural damage, but the airport remains open to those pilots who still want to wing it (literally).
The Oakland colisseum has beein inspected, is ok, and today's A's game is on. The 49'ers newly constructed Levi's stadium is undamaged and today's 49'ers preseason game is on. No reports of damage in San Francisco itself, according to the mayor there. The Caltrain commuter rail-line between SF and SJ is closed in order to inspect the tracks, but that's just their earthquake protocol, they don't expect any damage and the line should be up and running before the 49'ers game. Amtrack service between Sacramento and the bay area won't be running indefinitely until track inspections are completed. (Those tracks come much closer to the center.) Other than that, public transit is running normally. (Actually, some extra busses have been put into service, but that's because of the sports events, not the earthquake.) BART is running normally. Reports from the port of Oakland say the big container cargo cranes there are shut down for inspection. It's just a precaution protocol again and there's no obvious evidence of damage to them. So it looks like damage is mostly localized in maybe a 20-mile diameter circle just north of Vallejo in the NE quadrant of the bay area. That includes the Napa vinyards and is kind of a semi-rural exurban area, so there may be some damage in more isolated areas where news hasn't come in yet.
Glad to see that you are okay Yazata! I hope that your family and friends are also okay. The latest reports in the media are suggesting it was a 6.0 magnitude earthquake. Hopefully, the aftershocks won't be too bad, especially since there appears to be over 80 people injured, some critically. Take care of yourself and keep safe!
Thanks for your concern. Everything is fine in Silicon valley. There's no reports of any damage where I live (about 50 miles from the quake epicenter). It's just another normal day here, apart from all the excitement on TV. Damage seems to be fairly significant in the southern Napa valley though. Other parts of the North Bay seem to have come through very well. That's geologically interesting. I'm just speculating now, but the Napa valley is a valley, after all. It has mountains and rock on both sides, with alluvial soil in the valley floor. Those kind of conditions can kind of localize and concentrate earthquake damage, as the softer soil starts to shake and the energy waves reflect back off the adjoining rock and create interference patterns. That's what happened in Kobe Japan. They saw streets where there was relatively little damage, while a short distance away entire highrises and elevated highways were shaken down. It all depended on whether the earthquake waves reflecting off the base of the adjoining mountains were adding or cancelling at a particular spot. (In addition, soil liquifaction had a huge role in making Kobe worse. In earthquakes, wet soil can take on a consistency like jello and loses its ability to sustain loads. There's less likelihood of that happening around here due to our California drought.)
You're alive! Truly a rattling experience, but hey, when you can sleep thru an earthquake it must not be THAT bad. I'll be waiting for Pat Robertson and Co. to come out this week with an official statement about how this is a warning judgment for San Francisco to repent. The next one will not let you off so easily. You could always move up here to Portland. Similar climate except for all the rain.
Is Pat still predicting a tsunami for you guys in the Pacific northwest? I can't remember why he was, but I'm sure he had a good reasonPlease Register or Log in to view the hidden image!
"If I heard the Lord right about 2006, the coasts of America will be lashed by storms," Robertson said May 8. On Wednesday, he added, "There well may be something as bad as a tsunami in the Pacific Northwest." Note this was over 8 years ago. Guess we're overdue..
God can't count, remember? Seven days, Methuselah's age, things like that. Please Register or Log in to view the hidden image! Yazata, I'm glad the damage was slight for most, but my first thought on seeing the 11km depth of the quake was this might be a foreshock. I hope I'm wrong. The drought-related uplift would almost certainly have some effect on previously-loaded faults, but the PTB have said there should be no increase in EQ probabilities or magnitudes.
The TV reporters interviewed a geologist from the US Geological Survey's Menlo Park earthquake laboratory a few hours ago and asked him about the earthquake's depth. He said that it was pretty typical for Northern California earthquakes. They didn't address the foreshock issue, but my impression is that there's a possibility that this is a foreshock of something as big or bigger, but other commentators seemed to think that the probability is pretty low. They are more concerned about aftershocks in the magnitude 5 range, which could conceivably cause already structurally damaged buildings to further collapse. Apparently there's about a 50% chance of that big an aftershock. Here's an interesting thing from the UC Berkeley seismological laboratory about trying to determine exactly what fault was responsible for this. It's estimated that there are more than 100 faults in the bay area and some remain unknown. The Napa valley remains particularly murky, because the valley's soft alluvial soil doesn't lend itself to displaying the the kind of obvious rupturing that mark the locations of the San Andreas and Hayward faults so graphically. http://seismo.berkeley.edu/blog/seismoblog.php/2014/08/24/which-fault-is-it It includes a shake-map that shows the limited geographical extent of the strong shaking with this one. By comparison, the shake-map for the 1989 Loma Prieta earthquake showed strong shaking across a much broader area. But... in that small area the shaking with this one was occasionally intense. Berkeley says that their instruments show the shaking's lateral accelerations reached half a g near the epicenter. (For Sciforums readers who don't already know, the 'magnitude' of an earthquake is a measure of how much total energy it releases. Magnitude doesn't necessarily correspond to the intensity of the shaking that one feels. The intensity of the shaking you feel is also a function of the geology beneath you and how far you are from the epicenter. If you're on soft moist soil that liquifies when shaken (like landfill for example) shaking can be very intense. But if you're on solid bedrock the same magnitude earthquake might not feel nearly as strong.)
I would have thought with the conditions you described for Napa Valley, that the damage could have been much worse (if your speculation is correct). Liquefaction in Kobe was worse because of landfill. A lot of the islands were man made, weren't they? And that was why it was so much worse there? But for its magnitude, Napa came out generally unscathed compared to Christchurch, in New Zealand, which saw most of the city condemned and leveled with a lot of liquefaction in the suburbs surrounding the city.
Some geologists believe that the drought may be causing more earthquakes. Colin Amos thinks that there's a direct link between human-caused groundwater depletion and increased seismicity and mountain uplift in California’s Sierra Nevada and Coast Ranges. http://www.nature.com/nature/journal/v509/n7501/full/nature13275.html
Check out "Quake Alert" from Google Chrome Apps. Nice little program. I monitor these quakes all the time for interest's sake. Just after the 6.0 in Napa area was a 6.9 in Peru, but the quake was ten times deeper. It shows as 101km deep. Which leads me to some questions about 'surface' activity like the groundwater depletion referenced in the paper above, or the popular cause right now of injection wells due to fracking.. I say 'surface', due to the scope of 100km the crustal movements driven by forces that are 100km, 200km and more; that actually cause this rock cycle we ride on. Can anyone with any earth science background provide some kind of actual numbers as to what kinds of forces we are actually talking about with continents adrift on the mantle? etc. Maybe even some calcs to determine what kind of forces were released during something like a 6.0, or an 8.0.
Here's an update from the USGS on the South Napa Earthquake. http://www.usgs.gov/newsroom/article.asp?ID=3980 The earthquake appears to be the work of the known West Napa Fault. This fault is responsible for the magnitude 5 Yountville earthquake in 2000 and the magnitude 6.3 Mare Island earthquake in 1898. Geologists on the scene have located and partially traced a surface rupture from the epicenter through the Napa Valley NNW for about 10km/6 mi from the epicenter. It looks like the west side of this rupture is displaced northwards about 2 inches relative to the east side. Then the rupture apparently skips east about a kilometer and picks up again for an unknown distance NNW from there. Surveying is ongoing. They suggest that the localized extent of the damage might be associated with the earthquake energy having been directed in this NNW direction, along with possible amplification effects due to the sedimentary soil in the valley floor. I'm sure that research on that is ongoing too.
I live on the Olympic Peninsula in Washington State. I also woke up at 3:20AM on that day, but I have no real idea why. It was very unusual.
