About Paul Bodin

Ask a seismologist!

Recent posts

• Follow Following 1

  How does Seattle's earthquake area compare to Wasatch Valley's?

  5 0 Not too personal at all! The Wasatch front is a real seismic hazard but it differs significantly from Seattle's. In Utah the predominant seismic hazard is from the range-bounding "normal" fault that runs all along the front and right through Salt Lake City. ("normal" here being geological jargon denoting a fault that is a dipping plane, with the block on top slipping down relative to the block on the bottom--like gravity was driving it.) Big normal faults create the beautiful mountains and valleys all across the Basin and Range, with the Sierra Nevada on the west and the Wasatch on the east moving ever so slowly apart. The Wasatch fault breaks in chunks that give rise to earthquakes in the M7+ range. Here's an image I stole from the USGS, showing the most recent breaks along the front according to geologists. The overall level of hazard is a bit less than that of Seattle. The USGS National Seismic Hazard Maps provide gobs of detail. Here's a quick overview in which reds are bad and greens good (as usual!) that gives you an intuitive feel for the distribution of hazard in the western US. Now this specific map represents a level of a specific frequency of ground shaking that can be expected with a probability of 2% in 50 years. This convoluted way of looking at things ends up being useful for planners, although it seems confusing to us mortals.  But think of it like a weather map showing the likelihood of strong rain, for example. You're more likely to get shook in Seattle over any 50 year period, then you are in Salt Lake. But both are pretty high. The difference in Seattle is diversity [Gee, who would have thought Seattle to be more diverse than Salt Lake City?]. The potential earthquake sources that contribute to Seattle's high hazard level include M9 megaquakes on the subduction interface out to the west of the city, deep earthquakes (like the 2001 Nisqually earthquake ) in the downgoing sea-floor slab, and crustal faults (like the Seattle Fault that runs right through the city). While the chance of an earthquake from any of the three sources is fairly low (Well, the Nisqually-type source seems to have a rather high recurrence rate, given very similar events in 1949 and 1965 ), they all conspire to form a fairly hefty hazard here. Paul Bodin answered in Earthquake! over 2 years ago Answer and comment »

• Follow Following 1

  do you think the time and effort spent worrying about natural disasters is justified?

  4 0 This is a really great question, I think. But it is a tough one to answer simply, in part because there are so many levels on which you've posed it (from time spent to psychological impact) and because there are so many uncertainties (for example, we don't know that event X is going to strike--is time spent preparing for it therefore wasted?). My short answer is this, and it is my personal opinion: I think we should spend less time worrying and fretting about possible disasters and relatively more effort in rational and sensible preparations and precautions that would prevent natural threats from becoming disasters. Examples of sensible preparations and precaustions we can do about the earthquake threat include: 1) education, 2) threat monitoring, 3) developing and enforcing the most well-informed design and building codes, 4) encouraging and rewarding simple mitigation measures, and 5) having personal and family emergency plans and kits [but not going overboard on these]. For earthquakes--the only thing I can claim to know anything usefully quantitative about--one way to look at your question is to reduce it to a money question [dollars and "sense"?]. FEMA (the Federal Emergency Management Agency) has produced a valuable report, updated in 2008. In it they estimate that based on the best current thinking, earthquakes will cost annualized losses (AEL) within the state of Washington of $366,431,000. That is what the cost each year of the impacts of expected earthquakes affecting the state will be, averaged over time. The question becomes, what fraction of that should be spent to prepare for, and mitigate, those potential losses? Can we substantially lower this amount by spending relatively little? Or should we just shrug our shoulders and acknowledge that somebody will have to pay these costs eventually? [By the way, the report has other information of interest, like number of expected displaced households, and tons of debris expected to have to move, etc.] Another thing that makes this tough is that when a natural threat takes place--and you've prepared, it is difficult to be sure how much you've saved. How much worse would it have been had you not spent the effort? I think the disaster in Haiti demonstrates a worst-case scenario that has nothing to do with our circumstances. But it does illustrate what happens when society is absolutely unprepared. One final point is that we tend to focus on the Katrinas and Haitis and Sumatras that really blast a region and its inhabitants. Far more likely for earthquakes in Washington, and arguably what we should spend the most effort on, are scenarios where there are pockets of damage (as opposed to regional devastation) that may have significant economic impacts regionally. I imagine the port facilities being damaged such that industries can't ship materials easily, as one potential example. Or transportation corridors being disrupted so that business can't move materials around. We must acknowledge that we're going to get knocked down. We should be prepared to pick ourselves up, dust ourselves off, and get back to life--which should NOT be spent worrying about potential disasters! Paul Bodin answered in Earthquake! over 2 years ago Answer, comment & read 8 more answers »

• Comment on Paul Bodin's answer…

  0 0 Well I'll admit I dodged the supervolcano eruption effects question a bit. In part, I'm no vulcanologist. From what I've been able to gather, 'though, I'd say there's a great deal of uncertainty about just how severe the effects and how much of an impact on human society such a blowout would have. I didn't say it wouldn't be a big deal--look at what one fairly ordinary Icelandic eruption just did to European air travel last week! What I stand by, however, is that such a cataclysmic event is far (far) less likely than a much more ordinary eruption. Paul Bodin commented over 2 years ago

• Follow Following 1

  Probability of Cascadia Subduction Zone Earthquake

  1 0 Since there were no seismographs (and, even better, no seismologists!) around much more than a century ago, our evidence about how often Cascadia subduction zone earthquakes occur comes from what a lawyer might call "circumstantial evidence". Mostly, from tsunami deposits--characteristic sediments left behind when high tsunamis ran inland and left a layer of sand behind. Also from coastal tree stands in which the all the trees died at once, due to being submerged in saltwater as a result of deformation associated with a big event (and which we can date precisely using tree-rings). Chris Goldfinger, at Oregon State has shown that Cascadia earthquakes also cause submarine "turbidity currents" that are essentially mudflows that cascade down offshore canyons, and that can be sampled using sea floor coring devices, and the events dated. The size, or magnitude, of these ancient events may be related to how widespread the shaking was (and thus how widespread their resulting turbidite deposits are found). He's established a chronology of Cascadia subduction events that seems to indicate that the subduction zone is "segmented". He interprets the data as evidence that the southern portion tends to go off in relatively smaller earthquakes (M8-M8.5?) relatively frequently. But about half as often the entire margin breaks (like it did 310 years ago), from Cape Mendocino to Vancouver Island, in a walloping M9 earthquake. From a seismologist's perspective, I think these findings are all logical and make a sensible story. But since I'm not a geologist I retain a skeptical attitude about just how well one can identify the turbidites arising from individual earthquakes in different submarine channels. Ok, now for the probabilities. Yes the accepted 50-year probability of occurrence for a Cascadia Megaquake (sounds like something Hollywood would invent, no?) is generally regarded as 10%-15%. You could do worse than saying that if in any 500 year period I'm likely to have one M9 earthquake, then in 10% of that time interval (i.e. 50 years) I've got 10% chance of an M9. I know I know you think that a 50 year period starting at 450 years after the last earthquake will have a higher chance than one starting 100 years afterward. We call that "time dependent" probability, and it sounds grand. The problem is that you need to know a LOT about the variability of your "500 year events", or time-dependent probabilites don't do any better at forecasting likelihoods of earthquakes then the simple calculation we just did. Goldfinger's results indeed suggest that the likelihood of a strong southern Cascadia Subduction Zone earthquake is something like twice as high as for the northern part of the zone, which only breaks in great M9 beasts. Now for my answer to the triggering question: Not that I know of. While it is clear that stress changes and seismic waves from one earthquake can indeed cause other earthquakes to happen, simply not enough is currently known about how this works to enable us to guess how likely it is to happen with any particular earthquake. But my guess is that it is probably fairly rare since I'm not aware of any historical examples of subduction earthquakes being followed by a large crustal earthquake in the overriding plate (and I was looking for this after the 2004 Sumatra earthquake and last month's Chile earthquake). Paul Bodin answered in Earthquake! over 2 years ago Answer, comment & read 2 more answers »

• Follow Following 1

  During an earthquake, could a sink hole ever suddenly appear and swallow you up? Or is that Hollywood fiction?

  1 0 During an earthquake we observe several different sorts of ground failures. Let's imagine the earthquake process in a couple of stages, First, driven by stressed rock, a fault plane ruptures (i.e., one side moves relative to the other). This release of elastic energy -- like a stretched rubber band, but rather stored in the stretched rocks around the fault, radiates outward as seismic waves in all directions. These seismic waves cruise outward through the rock and, near Earth's surface, interact with lots of just normal rocks and soils. But there are also pockets of soft weak soil, wet sandy muck (another technical term!), cliffs, and other topographic features. Seismic waves can cause failures in these weak features, too. So: Ground failure #1 is where a fault rupture itself intersects Earth's surface. Different types of faults lead to different detailed patterns in the faulting. But since the dominant motion of a fault rupture is shear -- the sides slide along against each other -- fault breaks aren't likely to swallow anybody up! This just doesn't happen. Ground failure #2 is related to liquefaction--where a wet sandy soil is shaken so violently that it looses cohesion and compacts--often squirting water and sand out onto the surface--and looses it's bearing capacity; buildings may list, or even fall over. If there is the slightest slope, liquefied soils will flow, and may break up into blocks. The wonderful picture of the Turnagain Heights liquefaction features in Anchorage that O my captain attached to his answer is a beautiful example of this type of ground failure. Ground failure #3 is triggered landslides. This one's easy, you shake a hillside and gravity tumbles it down. This can bury folks, like any landslide. However nothing opens up and swallows you. Yes I've spent a professional lifetime telling people not to worry, the ground WILL NOT open up and swallow you and then close again. THEN I took this picture after the ChiChi earthquake in Taiwan, 1999. My team and I couldn't figure out how---but this is the only thing I've ever seen that made believe it was possible....(!) Paul Bodin answered in Earthquake! over 2 years ago Answer, comment & read 4 more answers »

• Follow Following 1

  Are we really supposed to stand in door jambs during an earthquake?

  1 0 If you are clear-headed enough when you feel a strong earthquake to think "Hmmm. Let's see  ... now, do I stand in a doorway? Or ... maybe get under my desk? Or, no! I should run outside!" then you are a real cool customer and will have no problem surviving anything that happens. The couple of truly large earthquakes I've been in have taught me that my body (and the Earth) will do what they want, and I'm just a passive observer: "Oh my, I'm trying to get out of bed and I keep getting heaved back onto it!" or "Wow! Here I am out of doors..isn't that supposed to be a dumb place to be? How did I get here?". So I'm not the cool analytical sort during an earthquake, apparently. If you happen to be, then here's my prejudiced opinion for you to consider when the next large earrthquake strikes. I think it matters greatly where you are. If you are in a well-constructed office with sturdy furniture, then "Drop, Cover, and Hold" may be for you--protects you from projectile-books and falling ceiling tiles. If you are in an mud-chinked river-rock cabin with turf on the ceiling, then you best get outside ASAP, jumping underneath that flimsy card table isn't going to protect you from the tons of primitive building materials about to come your way. If you have no furniture to jump under and have a nice arched doorway with no door in it and far away from that big picture window in your living room...why then probably you should saunter over there and brace yourself in it. There are some advice videos  from SCEC (the Southern California Earthquake Consortium) available online by clicking here . There are some places I simply feel out of place being in. A parking structure in the city is one, the Alaskan Way Viaduct another, any elevator too. It is my plan not to be in one of those when the earthquake hits. Maybe someone else has good advice for these spots, if you can't avoid them. Paul Bodin answered in Earthquake! over 2 years ago Answer, comment & read 2 more answers »

• Follow Following 1

  Will the Yellowstone super volcano kill us all if it erupts?

  2 0 OK, you're asking a seismologist about a volcano and if any of my vulcanologist buddies read this I'll never hear the end of it... Let's clarify some obscure but important points. There are different kinds of volcanic eruptions, even at an individual volcanic center. At Yellowstone the most common kind of eruption is hydrothermal --superheated steam or water blasts out craters as large as half a mile across! But that isn't going to strongly affect the US. Magmatic (i.e. lava--molten rock -- the real stuff!) eruptions vary in the chemistry and physical properties of the magma they emit from soupy, runny, basalt like a Hawaiian volcano (picture lava flows running along the ground) to sticky chunky dry goobery gunk called rhyolite that can be as explosive as all get out. The commonest (i.e. most likely) eruptions are smaller ones, and caldera-forming super volcano explosions being the rarest. In fact. at Yellowstone the real bad boy explosions that frame the main point of your question occurred 2.1 million years ago and 1.3 million years ago and 0.64 million years ago. Based on average recurrence of these events, we are deep into a cycle and may only have to wait another 90,000 years for another. [I'm no statistician, but in order to actually answer your last question I just calculated a rough back-of-the envelope estimate of ~0.02% chance of a supervolcano eruption in 100 years, and I made some assuptions that make this rather a high-end estimate]. The most likely eruption, either hydrothermal or magmatic, would NOT be a super volcano, but a regular-sized family-friendly volcanic episode. It would be big news. It would close the Yellowstone National Park. It would likely put a thin layer of volcanic ash all over the northern tier of states. It would disrupt the heck out of air traffic. But it would not kill us all, or wipe out our civilization. (too bad, some might say!) A supervolcano could be bad news, could disrupt agriculture downwind and could even affect global weather patterns (which actually could help forestall global warming?!). I still don't think it would come close to killing us all or wiping out the country. Paul Bodin answered in Earthquake! over 2 years ago Answer, comment & read 6 more answers »

• Follow Following 1

  Is it true I should have water and a whistle in every room?

  3 0 I hope another answerer has better knowledge of this than I do. My experience with people who haven't survived earthquakes has been mostly in cities and towns in developing economies. Heavy rock and/or mud structures without significant resiliance when shaken that pretty effectively collapse and crunch the denizens outright. Not pleasant, but it really kind of suggests that water and a whistle wouldn't be of much value in that circumstance. Of course, in Seattle I don't think there has been anyone trapped in an earthquake-collapsed structure, so the statistics wouldn't be useful here, either. I don't mean to belittle the importance of individuals preparing for earthquakes, but I don't think the best preparations involve worrying from moment to moment about our proximity to whistles and water. Rather it is to ensure that society enforces earthquake-resistant design codes and construction practices. Engineers are perfectly capable of designing structures that will withstand any shaking our faults are liable to throw at them. It is also critical to mitigate easy-to-remedy problems (water heaters not secured, heavy objects on high shelves not secured, structures adequately tied to foundations, etc.), and to have an "earthquake kit " (and yes, it does have a whistle and water in it!) available in a secure place in your house or apartment. Paul Bodin answered in Earthquake! over 2 years ago Answer, comment & read 3 more answers »

• Comment on Paul Bodin's answer…

  0 0 Ah! Geological jargon. To be technical, a fault is a planar surface within Earth across which there is a relative displacement of the two sides. [A similar surface, but with no relative displacement, is called a "joint"]. Anyway, you are right that boundaries between tectonic plates are fault zones. And you are right that faults often follow geographic features--like rivers or coastlines; usually because the fault either grinds up the rock or there is a big contrast of rock types across the fault that leads to the formation of a prominent topographic feature. But faults can also form within rock masses. They are just zones of weakness that slip in responses to stresses in the rock. And plate tectonics is a sloppy business...not all the relative displacement is necessarily taken up by the main plate boundary fault. This results in residual stresses that drive slip on secondary faults (such as the Seattle fault), albeit at much slower rates. One model to think about to picture faults relieving stresses in solids is to mix yourself a nice gin and tonic. There--isn't that better? Ooops, forgot the demo part...now drop an ice cube or two in and in no time they'll be some loud pops. Those are ice quakes as faults in the ice cubes slip suddenly in order to relieve the thermal stresses you just created in the ice cube by dropping it into room temperature fluid! Paul Bodin commented over 2 years ago

• Follow Following 1

  Could a significant earthquake set off Mt. Rainier?

  5 0 I'm glad you don't suffer from those dreams now. When I was a kid I dreamed of wolves attacking my house and ... well, I digress. This is really a great question. And the proof is that some scientists say earthquakes can affect volcanic eruptions and some say no way . If we can't agree, then I guess I really have no right to give you a "yes" or "no" answer. Ok, enough of a disclaimer; now I can tell you what I think... There is some statistical evidence that there were more eruptions after large Chilean earthquakes in 1906 and 1960. But the mechanism by which this "triggering" might happen isn't clear. There's also lots of anecdotal evidence of particular eruptions following certain earthquakes. But such stories suggesting correlation are not entirely convincing, nor do they demand causality . However,  it sure seems plausible that shaking from seismic waves can jostles magma and make it move around--and rise toward the surface if it is so inclined. But it takes magma time to work it's way to the surface. So the difficulty in observing earthquake-triggered eruptions, then (according to me) is that there are likely to be variable delays between the triggering earthquake and the ensuing eruption. Drawing the connection between any given earthquake and some ensuing eruption is uncertain. I also think that as our capabilities to monitor both ground motion from earthquakes and the deformational processes that precede eruptions, we will be able to x-ray this whole process and answer this question concretely. Paul Bodin answered in Earthquake! over 2 years ago Answer, comment & read 3 more answers »

• See all of my 0 Questions , 10 Answers and 2 Comments