10 ms·
How long should we wait for an overdue earthquake on the San Andreas?
- lordnacho 10y agoWhat does an historic earthquake look like in the layers of rock? How do they know when they occurred?
- cossatot 10y agoThe science of finding out the (pre-)historic earthquake history is called 'paleoseismology'. You can read about it from a variety of sources. In most instances the earthquakes are dated by finding carbon-bearing material in deposits that look like they were created during the earthquake, and doing radiocarbon dating of them. The ages may be bracketed by radiocarbon dating of sediments that were clearly broken by the earthquake (and are therefore older) and ones that overlie the broken rocks (and are therefore younger). In a few other instances, earthquakes can be dated by tree-ring dating; for example during big subduction zone earthquakes, the coast often subsides by a meter or two, which will put some forested beaches under sea level (or at least high tide level) and kill all of the trees that can't deal with salt water. In others, the dates of sediment layers broken or caused by earthquakes can be dated through other means, or correlated with climate events of known time. Some example of deformed and undeformed sediments in the Wrightwood trench site on the San Andreas is here[0,1]. [2] is from the nearby San Jacinto fault. [3] has a lot of images. [4] is a good introduction to the science with good pictures. [0]: http://www.bssaonline.org/content/97/4/1054/F14.large.jpg http://www.bssaonline.org/content/97/4/1054/F14.large.jpg [1]: http://www.bssaonline.org/content/92/7/2726/F11.large.jpg http://www.bssaonline.org/content/92/7/2726/F11.large.jpg [2]: http://lithosphere.gsapubs.org/content/7/3/211/F6.large.jpg http://lithosphere.gsapubs.org/content/7/3/211/F6.large.jpg [3]: http://earthquake.usgs.gov/research/external/reports/04HQGR0083.pdf http://earthquake.usgs.gov/research/external/reports/04HQGR0... [4]: http://isites.harvard.edu/fs/docs/icb.topic988563.files/EPS203_paleoseis5r.pdf http://isites.harvard.edu/fs/docs/icb.topic988563.files/EPS2...
- sintaxi 10y agoIf it doesn't happen this year, just wait longer.
- stillworks 10y agowinning by induction
- DavidSJ 10y agoSubduction actually.
- sveme 10y agoSome fault lines seem to accumulate energy, so the longer the waiting period between two earthquakes, the stronger it gets. Is it the same for San Andreas, so that more frequent earthquakes would actually be beneficial as they would be easier to handle structurally?
- tqkxzugoaupvwqr 10y agoI’m not an expert and I have the same understanding. Futuristic earthquake mitigation approaches talk about inducing small, non-destructive earthquakes in a controlled way to reduce the magnitude. The goal is to completely manage earthquakes.
- iamcreasy 10y agoThat's insanely cool!
- sbuttgereit 10y agoOh sure... now you want to frack. ;-)
- jessaustin 10y agoMaybe Oklahoma and Arkansas are the best places to go to avoid "The Big One"?
- ScottBurson 10y agoNot as good an idea as it sounds. The problem is that the largest earthquakes release massive amounts of energy. Each point on the Richter scale corresponds to about a factor of 30 in energy. So to release the energy of one magnitude-7 quake would take some 900 magnitude-5 quakes. And a 5 in a populated area can still do a little damage. Can you imagine how people would feel about having one of these a week for 20 years?
- GregBuchholz 10y agoWhy not 810,000 Magnitude 3 quakes?
- rwmj 10y agoThere's a ton of data on the very regularly occurring (hourly) small earthquakes around the world available from USGS: http://earthquake.usgs.gov/earthquakes/ http://earthquake.usgs.gov/earthquakes/ I'd like to see whether this analysis works on this rich data, not on the very sparse data set of San Andreas earthquakes.
- ejcx 10y agoSo, we aren't only overdue but a quake seems imminent? The upper bound of time between quakes was very slim. This is a stupid and selfish question, but what does a quake on the San Andres fault mean for San Francisco? My knowledge of all of this is based on 4th grade science.
- celticninja 10y agoBad news. Whilst building codes may be better than in the past, due to population density the risks of a high number of deaths is significant.
- abalos 10y agoI would imagine a very significant portion if the Marina district just turning into rubble unfortunately. I'm hoping this doesn't happen until buildings have a chance to improve even more.
- cloudjacker 10y agoNo chance for improvement. New buildings follow better building codes, such as the tall ones that may sway like Japanese skyscrapers, old buildings have no mandate to improve, and San Francisco was mostly built after the 1906 earthquake, with many of the walkups that litter the view being in the 1920s - 1940s. From my understanding, any hope you might have is neglecting a reality that an overdue earthquake will cause devastation largely reserved for the third world.
- cloudjacker 10y agoSan Francisco can't even mandate building codes on sidewalks, which involves the most marginalized and disenfranchised inhabitants, you really think they could come to a conclusion that involves landlords?
- peterbraden 10y agoThis is fear mongering. The tectonic structure of the SA fault means that the upper bound for magnitude is limited, and building codes are really good. Up in Portland and Seattle, the risk for high numbers of causalties is far greater due to the subduction fault rather than the transverse fault.
- brador 10y agoQuestion: what happens to land rights after a quake? Since the quake moves land around, stretching in parts and destroying land into cracks in others. Do property lines get redrawn? Who owns any newly created land space? Is it fair game for anyone to claim?
- celticninja 10y agoIt doest really work like that, it's not like new land is created by pushing out into the sea, but even if it was the property owners boundary is likely the sea, therefore the land is incorporated within their area.
- slazaro 10y agoBut what if you have a fence that gets shifted around, and no longer matches the boundaries in the property maps?
- brador 10y agoSay there's a crack or fissure that opens up, creating new "space". Someone then fills that crack with soil making new "land". Or say the land under a fence moves. Since land ownership diagrams contain specific measurements, are they redrawn? Replaced? Accepted? Measurements ignored and features used instead (apple tree to 7th fence post)? If my property deed says my yard is 20 metres wide, but post earthquake it's 21 because a 1 metre wide split occured in it what happens when I sell? Is accuracy thrown out the window?
- evgen 10y agoMy best guess would be that the state would claim original ownership of the new land. If you take a small coastal lot and then start building landfill out into the ocean you are going to have a hard time convincing the state that you own the property without some pre-existing contract with the appropriate regulatory bodies stating this when you started construction.
- JshWright 10y ago
- ZenoArrow 10y agoWhat I can't understand is that after the 1906 San Francisco earthquake, where "Over 80% of the city was destroyed by the earthquake and fire" ( https://en.wikipedia.org/wiki/1906_San_Francisco_earthquake https://en.wikipedia.org/wiki/1906_San_Francisco_earthquake ), why on earth was it rebuilt? Surely that's a sign to move the new city elsewhere?
- onion2k 10y agoYou're only looking at the downside risk. There are huge upsides to the area - notably the San Francisco Bay is a natural harbor, which makes it a really good place to put a port. The promise of wealth from trade meant people would live them pretty much regardless of the downsides.
- ZenoArrow 10y agoFine, but what's likely to be cheaper, building an artificial harbour away from the fault line or rebuilding a damaged city every 100 years or so?
- creshal 10y agoThe fault line is exactly on the coast and 800 miles long. Rebuilding affected cities every 100 years or so is cheaper than re-routing all ship traffic affecting a quarter of the US.
- deleted 10y ago[deleted]
- onion2k 10y agoYou'd have to go a long way from the San Francisco Bay to be a safe distance away from the fault line, which would have a dramatic impact on the costs of operating the port - it'd add hundreds of miles to the distance you'd need to move the goods off the ships to where they were needed. Factoring that additional cost in over the decades between earthquakes (SF burned down quite regularly prior to 1906), I wouldn't be surprised if it was actually cheaper to rebuild the city occasionally.
- marcosscriven 10y agoPossibly a silly question, but... I hear the term 'overdue' applied particularly to earthquakes, rather than any other naturally occurring event. Does this mean 'overdue' in the same sense that rolling a six is 'overdue' if you've not seen one after six rolls?
- 991219921 10y agoNo, It means that the tension between tectonic plates steadily builds up, so an earthquake is more likely.
- marcosscriven 10y agoI see - the article though seems to talk about 'surface-breaking' earthquakes occurring every 100 years in that region, and that we're now at 159 years without one. This idea of a time expectation doesn't seem to match your explanation (which seems more intuitive to me).
- rgossiaux 10y agoThey're the same, really -- those quakes happen every 100 years because that's how long it takes for that much pressure to build up. 159 years without one means there's already going to be quite a lot of pressure built up that's going to have to give way sooner or later.
- sevenless 10y agoWe know that fluid injections for fracking can cause earthquakes. How about injecting some extremely viscous fluid deep underground within the plate boundaries? So it can release the shear force over months or years rather than seconds. Something like pitch (https://en.wikipedia.org/wiki/Pitch_drop_experiment https://en.wikipedia.org/wiki/Pitch_drop_experiment) Of course, the major problem with trying quake mitigation strategies might be the legal responsibility if you cause a quake.
- fit2rule 10y agoI lived in SoCal and worked in SFO for some decades and witnessed both the Northridge and the Oakland quakes first-hand, narrowly avoiding personal injury or even death in both cases (big things falling around me), and the conclusion I made after these events, which I eventually acted on, was simply put thus: GTFO! I really didn't want to be there when the Big One happened, nor even some of the minor small ones, so I've moved to Central Europe where such things have a lower chance of happening .. in a way, I have a perverse desire to see The Big One happen from so far away, but I always dread the mind-game of trying to conceive what SoCal will be like, afterwards. I truly dread the idea, and I honestly can't understand how any society with scientific awareness of its surroundings can nevertheless commit to building so much expensive civilization and infrastructure in a known catastrophe zone. I guess its just a matter of momentum, but I sure wish the citizenry of the PNW and SoCal would prepare themselves for this event a bit better. It seems so defeatist to continue to build things in that area, knowing it could fall into the sea in a moment, and there is nothing we could do about it. California should just be a massive nature park stripped of all human involvement, just in case, but of course this is never going to happen, so if The Big One does happen in my lifetime, its just going to be a massive tragedy no matter what we humans could have done about it with all our science and stuff. Argh!
- ghaff 10y agoI guess if I lived through two significant earthquakes in that way, I'd probably have had a thought along the lines of "This is a sign to move" as well. >It seems so defeatist to continue to build things in that area Fatalistic is probably the better word. I can buy an old missile depot in the Midwest and stock it up with supplies and prepare myself for the zombie apocalypse or whatever. Or I can live somewhere I enjoy, and has good opportunities, etc. and not worry too much about events I don't have a lot of control over or a lot of insight into their probabilities. Of course, there are situations between those two extremes and it's not unreasonable IMO to include "the Big One might hit" into a calculus for evaluating moving to or staying on the West coast. (As with living in areas with a lot of potential for floods, hurricanes, and tornadoes.) Actually turns out Las Vegas, for example, scores pretty well on non-disaster metrics. One reason a lot of datacenters are there--in addition to evaporative cooling.
- qrendel 10y agoI was under the impression that the bigger danger was the expected eventual earthquake of the Cascadia Subduction Zone, potentially leading to tens of thousands killed or injured and millions more displaced.[1][2] [1] http://www.newyorker.com/magazine/2015/07/20/the-really-big-one http://www.newyorker.com/magazine/2015/07/20/the-really-big-... [2] https://en.wikipedia.org/wiki/Cascadia_subduction_zone#Earthquakes https://en.wikipedia.org/wiki/Cascadia_subduction_zone#Earth...
- cossatot 10y agoThe damage from a Cascadia rupture is going to be more widespread but the ground shaking in the metro areas may be less than for the San Andreas because the San Andreas hits the surface quite close to populated areas (LA also has more people that WA and OR combined). The intensity of ground shaking decreases with distance due to geometric spreading and energy absorption by the intervening rock mass. Cascading ruptures are also every 500 years (or so) vs every 100 years, so the hazard per year is less. But yes, both are major concerns.
- int_19h 10y agoAlso, speaking of other faults, WA also has the smaller, but much more shallow, Seattle fault. Because it's so much closer to the surface, and right under the city, it can potentially do more localized damage than Cascadia. (There are other dangerous faults like that in Puget Sound region, but Seattle fault gets special attention because of how many densely populated Seattle metro areas sit literally right on top of it.)
- Cortexia 10y agoPeople always say Hayward Fault is more troubling for California because so much is built directly ON the fault.
- Cortexia 10y agoHopefully San Andreas will wait another 10 years, because by that time there will be no Nuclear Reactors operating in California. We are down to only ONE, and it will shut down within the next 6 years. PG&E is getting out of Nukes.