Jon Lebkowsky (jonl) Tue 26 Apr 11 05:30
Inkwell usually hosts discussions about books, but this conversation is a little different. The recent Great East Japan Earthquake and tsunami in Japan (http://en.wikipedia.org/wiki/Earthquake_Japan_2011) was, according to Wikipedia, "one of the five most powerful earthquakes in the world overall since modern record-keeping began in 1900," The 9.0 magnitude quake actually shifted the earth on its axis and moved Honshu 7.9 feet east, and triggered a major tsunami. This massive quake triggered much interest in, and discussion about, earthquakes in general. Here on the WELL, we have a forum dedicated to discussion of earthquakes, and it's been busy. We've invited the forum host, geologist Andrew Alden, to spend the next couple of weeks in Inkwell talking about this recent quake, and earthquakes in general. According to Andrew, quakes are "natural, more widespread than people think, challenge society because of their long cycles exceeding human lifetimes, are survivable and interesting, can topple the mightiest nation if not handled well, and are not well reported by American media." What can we learn from Japan's example? From Sumatra's example? Andrew Alden has been writing about geology for About.com since 1997, but in fact his involvement with seismology and the public began on the Well five years earlier as host of the Earthquakes conference, whre his baptism by fire was the Northridge earthquake in 1994. He has a B.A. in geology and worked for the U.S. Geological Survey for a span of eight years that included the Coalinga earthquake and the eruption of Mount St. Helens. He experienced the 1957 Daly City quake, the 1989 Loma Prieta quake, and countless smaller jigglers in the San Francisco Bay area. He lives in Oakland, not 3 kilometers from the Hayward fault. Mark McDonough will lead the conversation with Andrew. Mark has been a geology enthusiast since childhood, when he actually enjoyed being dragged to quarries and fossil beds in upstate New York by his "rockhound" father. After completing about 2/3rd of a geology major, he realized that his skills in allied sciences like math and physics fell a wee bit short of those required by a professional scientist, but he's kept in touch with the field ever since. He has an interest in the history of mining and has managed to visit many Western mining sites without once falling into a shaft. He is also interested in catastrophes of all kinds - earthquakes, asteroid strikes, tsunamis, you name it. He maintains a somewhat rarely updated web page on the subject at http://www.well.com/~mcdee/Catastrophe.html Other relevant links: Earthquakes at About.com: http://geology.about.com/od/earthquakes/Earthquakes.htm World quake map: http://earthquake.usgs.gov/earthquakes/recenteqsww/ Welcome, Andrew and Mark!
Mark McDonough (mcdee) Tue 26 Apr 11 08:19
Howdy! Andrew, to start things off here, just how big was the recent quake in Japan compared to past earthquakes in the US (for example, the San Francisco quake of 1906)? Are there any places in the US subject to quakes that large?
Andrew Alden (alden) Tue 26 Apr 11 09:40
Sizing earthquakes isn't an exact science, even though we are always given precise-looking numbers for them. The most basic scientific measurement is the magnitude, which measures purely the energy involved. That's like ranking basketball players by their height alone. We'll get into that more over the next two weeks, I'm sure, but for now I'll stick to magnitude. The Japan quake is being called a magnitude 9.0 event at the moment. Things change as the seismologists get more complete records from around the world; for instance the Sumatra quake of 26 December 2004 was upgraded a couple tenths of a point. But I think 9.0 will stand. The U.S. has had a quake larger than that -- the 1964 Alaska (Good Friday) event, which was a 9.2. The 1906 San Francisco quake doesn't even make the list of the biggest quakes, being something like 7.8. But I would argue that it was bigger in the human sense. We also had a comparable earthquake in 1700, in the Pacific Northwest. The tectonics of the Pacific Northwest is the same as Japan, and the same as Sumatra. So what we saw "over there" is very relevant to the United States. The 1700 quake is estimated to have been a magnitude-9 event, and what happened before will surely happen again.
Mark McDonough (mcdee) Tue 26 Apr 11 10:13
Yes, there was a certain amount of criticism of the Japanese for not realizing that Fukushima was subject to enormous earthquakes and tsunamis. If I recall correctly, the last major earthquake of that size in the area was almost 1,000 years ago. Granted, we have the excuse that only Native Americans were living in the Pacific Northwest in 1700, but I've never talked to anyone from that part of the country who had any idea that it was subject to major earthquake hazards. Are there any other earthquake hazard areas in the US that might be a surprise to people? I felt a couple (very small) when I lived in Providence, Rhode Island.
Andrew Alden (alden) Tue 26 Apr 11 10:45
I may live in an especially well informed cocoon, because I know that almost no place in the US is NOT affected by earthquakes. But I do think nonetheless that awareness is growing. It ought to be part of every state history course in Massachusetts, for instance, that Boston was widely damaged in 1755. Virginia had a damaging magnitude-5 event in 1897. Charleston, South Carolina, had a major event in 1886, estimated at M 7.3. The Missouri-Arkansas-Tennessee-Kentucky region was devastated by a series of magnitude-7 and 8 events 200 years ago; in fact, this coming Thursday there will be a huge earthquake drill involving those states and seven more, stretching from Oklahoma to South Carolina as part of a commemoration: see <http://www.shakeout.org/centralus/> for that.
Mark McDonough (mcdee) Tue 26 Apr 11 11:50
Yes, I think that geology buffs do live in a well-informed cocoon on these sorts of issues. I lived in Boston for a number of years and never ran into anyone who had any idea there could be a serious earthquake there. I think more people are aware of the New Madrid earthquakes of 1811-12 - those Missouri-Arkansas-Tennessee-Kentucky quakes. Ironically, some of that awareness comes from a bizarre episode about 20 years ago when someone widely convinced people that another huge quake was going to happen any day. Which raises the whole issue of earthquake prediction. Is it still pretty much useless? It seems I only run into two sorts of predictions - very specific ones by cranks that turn out to be wrong, and very general ones from scientists which are presumably more accurate, but almost equally useless ("there is a 50% chance of a magnitude 7 or greater earthquake in [wherever] over the next 40 years"). Any signs of progress on that front?
Andrew Alden (alden) Tue 26 Apr 11 13:26
Seismology is still a young science, and a difficult one especially if you want to help people. Many seismologists point to that motive, and I think even the most mathematically oriented theorists acquire it once they've been through the process of turning earthquakes into data. So let's grant that every seismologist really wants to predict earthquakes, not just model the deep Earth and map the interior and so on. But there are only whispers of progress in truly predicting earthquakes. The search party has checked out the obvious places, so to speak, and has since spread out into the underbrush looking for clues. Where seismology has made a big difference is in mapping active faults and measuring plate motions all around the world. That's good, basic data. They claim that earthquake forecasts, rather than predictions, are now useful -- as you say, X percent chance of a magnitude-Y event during the next Z years in area W. But even those are primitive science, no offense meant to the seismologists because it's the best they can do. And we know that the forecasts fail, in that most of the notable quakes have never been forecasted. That is a discouraging way to conduct science, and most practitioners are resigned to incremental advances. That attitude, by the way, accounts for some of the vehemence with which seismologists respond to would-be predictors. Seismologists have had their hopes cruelly dashed for a hundred years. I won't speak for them, but I hate to see lay people clutch at rumors and espouse the most obvious flim-flam when it comes to quake prediction. I hate it because I sympathize. Earthquakes are nightmarish things, coming with no warning and disrupting the foundation of the solid ground itself! Earthquakes are like the very threat of death; they're practically designed to create anxiety. For a highly abstract science, seismology is fraught with strong emotions.
Mark McDonough (mcdee) Tue 26 Apr 11 14:00
Yes, and anyone who's experienced an earthquake can understand why. I've been lucky - I think my biggest was a 3.5, but even that was a little unsettling. Speaking of magnitude, the recent Japanese quake was a 9.0. Is that about as big as they get?
Andrew Alden (alden) Tue 26 Apr 11 16:50
They get a lot bigger, but it doesn't look like much on the magnitude scale. The largest quake on record was 9.5, the 22 May 1960 Chile earthquake. Oh, just half a unit greater -- but the magnitude scale is logarithmic. That number represents an exponent. So the latest Japanese event, at 9.0, is a small fraction of that in terms of energy, about one-fourteenth the size. The 1964 Alaska and 2004 Sumatra quakes had five times the energy of the March 2011 event. Whatever. They're all horrible. The highest realistic magnitude possible on Earth? Well, let's look at Chile, the biggest. Its rupture zone was estimated to have been 1000 kilometers long, and there's about 1500 km of possible rupture available on that edge of the plate boundary. If you crack all of that at once, you've got one and a half times the energy, or another 0.2 magnitude units, for a theoretical maximum of 9.7. That's close enough for me. You simply can't line up enough lithospheric rock and stress it to rupture to get a larger event on this planet. But frankly, if you're near the thing when it lets loose, a magnitude 7 event is just as bad as a larger one. The experience is that the bigger events last longer, so the rubble bounces more. You also have to recall that the March quake was complicated, as it was in Indonesia, by a monstrous tsunami. It will take some concerted research to separate their effects. We will find, as we did in 1906, that buildings could survive shaking but not the aftermath -- fire in San Francisco's case, flood in Japan's.
Mark McDonough (mcdee) Tue 26 Apr 11 17:49
It seems like we've been getting an unusual number of big quakes recently. There was Chile in 1960 and Alaska in 1964, and then nothing of that magnitude for decades. Suddenly we've had two major quakes fairly close together. Is it possible that really major earthquakes do come in groups, or is it more likely to be just the random bunching of fairly rare events?
Andrew Alden (alden) Tue 26 Apr 11 19:41
It's even worse than that: we had no magnitude-9 events at all before 1952 (there was a 9.0 in Kamchatka that year). But yes, truly random events are not evenly spaced -- if they were, that would be a pattern. We have no way of saying anything about it given the shortness of the record, which is barely over 100 years. What I said earlier about the imprecision of earthquake measurements applies doubly to events before the advent of seismometers. We look at those earthquakes through the evidence of written accounts and that's pretty much it. Descriptions like that can tell us about the intensity of an earthquake -- how *bad* it is at location X rather than how *big* it is in an absolute sense -- and we can only make estimates, with a large amount of uncertainty, about its magnitude. Intensity, Burton Richter once said, is like how strong a signal you get from a radio station, whereas magnitude is the power the station broadcasts at. You can see how fuzzy the numbers might be when you try to estmate magnitude from written accounts of intensity. Seismologists are scientists, and they are deeply familiar with the concept of uncertainty. We can say exactly how fuzzy the numbers are, and we must be constrained by that fuzziness. It's like the same problem in astronomy, when a telescope gives us a fuzzy image. The scientist knows that trying to sharpen that picture yields untrustworthy artifacts. All of this goes profoundly against human nature; we're wired to see patterns in uncertain conditions. So in sum, lay people see patterns in randomness that feel valid, while seismologists look like fuddy-duddies for holding back and not seeing the face on Mars, as it were. If we had descended from cats instead of monkeys, we might be better scientists. But I suppose we'd be prone to different illusions. Anyway, we have no good evidence to say anything about long-term global trends in earthquakes.
Jon Lebkowsky (jonl) Wed 27 Apr 11 05:37
If you're reading this discussion but you're not a member of the WELL, you can still ask a question or add a comment by sending via email to inkwell at well.com.
Mark McDonough (mcdee) Wed 27 Apr 11 08:22
When you say no 9.0 events before 1952, you mean since reasonably accurate and modern records were kept, right? How far back can we go in terms of estimating the magnitude of historical earthquakes?
Gary Greenberg (gberg) Wed 27 Apr 11 09:11
> If we had descended from cats instead of monkeys, we might be better scientists. That gets my vote for quote of the week.
David Gans (tnf) Wed 27 Apr 11 09:11
Welcome, Andrew and Mark! Thank you for this topic. > If we had descended from cats instead of monkeys, we might be better scien- > tists. I just love that. I am a California coastal resident for all of my 57 years, and I have lived through a couple of major quakes, literally hundreds of smaller but perceptible quakes and thousands we never even noticed. I suppose we're all pretty philosophical about it, but I prefer this to the certainty of crippling weather every year in other regions, etc. I want to put in a good word for Andrew as a geology guide. He took a carload of WELL neighbors on a tour of the Bay Area a while back, showing us some of the oldest exposed rocks in this amazingly complex region. He's very good at explaining this stuff! Can you tell us a bit about why the Pacific Rim is referred to as the "ring of fire" and why there are more quakes and vocanoes here than around the Atlantic? (P.S. John McPhee's "Assembling California" concludes with a lengthy account of the 1989 Loma Prieta quake and how it went down in various corners of the affected area.)
David Gans (tnf) Wed 27 Apr 11 09:11
descend into a fractal hell of meta-truthiness (jmcarlin) Wed 27 Apr 11 10:39
Like many others, I'm always interested in reading about "what are the odds it's going to happen to me". But I'm also aware that we've had quakes that were on an unknown fault lines and I've even read in the media (I know, I know) that quakes can occur not on a fault line presumably due to other geological forces. Is the later true or just media mis-reporting? Another question that I tried to research and failed was to try to see how close my house is to a fault line. I could not find detailed enough maps to indicate that. Are such maps available online?
Peter Meuleners (pjm) Wed 27 Apr 11 10:58
I am going to spam the world with that cats/monkeys quote, with attribution of course.
Andrew Alden (alden) Wed 27 Apr 11 11:05
Mark: Seismographs were first devised in the late 1800s, and only after 1900 was the most rudimentary worldwide network possible. Ever since then, we've caught all the great (M 8 size) events. Anything older you might call prehistoric. But our estimates of earlier events get better as we learn about the typical behavior of different fault zones and early building types. As ancient records are translated and analyzed, we're getting a better idea of longer-term seismicity. It's not a dead end for research, especially for records like the Chinese ones. Still older earthquakes are studied with methods similar to those that archeologists use: digging trenches across active faults and dating the traces of old quakes. Paleoseismology is a field with great potential, and California does a lot of it. We can go back as far as carbon-14 and trench safety allow, potentially tens of thousands of years. That ought to be enough to capture the typical earthquake cycle even in the quietest active regions--assuming our working theory is valid. David: To visualize the "ring of fire," start with the picture of a big pot of soup simmering on a stove, with the water stirring by convection and islands of scum floating on top. The stove burner is old and funky, so one side gets a little more heat than the rest. Most of the time the soup surface is clean on that side, but every now and then the scum breaks up and wanders over it. Very simple picture, in fact too simple. Take that pot and turn it into a sphere instead, covered with soup. Turn the heat way down and blow on the soup instead. The tectonics of the real Earth is governed by cooling of the top more than heating from below, but you'll still get clumpiness, with the scum (continents) drifting around and joining and splitting while the patches of clean surface (oceanic crust) grow and shrink. The Pacific, today, is a very large patch of oceanic crust that rises into existence at a long seafloor spreading zone near South America, spreads apart in both directions, and plunges back down at the edges. The plunging part is where long volcano chains typically form. So (going clockwise) you've got volcanoes in New Zealand, eastern Indonesia, the Philippines, Japan, Kamchatka, the Aleutian Island arc, the US Pacific Northwest, and Central and South America. That's the ring of fire. The Atlantic is a much simpler ocean, one that's opening up passively as the continents on either side pull apart. There's none of the subduction that feeds volcano chains anywhere in the Atlantic, except in the eastern Caribbean. It gets earthquakes and also tsunamis, some of them quite large, but they aren't like those you get around the Pacific. I cover the basics of plate tectonics on About.com at <http://geology.about.com/od/platetectonics/a/About-Plate-Tectonics.htm>
Peter Meuleners (pjm) Wed 27 Apr 11 11:09
Is the structure of Iceland different than in the Caribbean?
Andrew Alden (alden) Wed 27 Apr 11 11:36
Some slippage going on there while I was composing the last remark... jmcarlin: Earthquakes can happen without the ground breaking; in fact most of them don't break the ground. So in that sense you can have quakes without "faults." And here's the thing: mapping the Earth's rocks and faults and so on is damnably hard. Everything is covered with soil and landslides and cities and water. The rocks themselves have to be studied under the microscope and the newer generation of electronics. Making a geologic map is a tremendous effort, and each generation in a field area upgrades and reinterprets the map, and even so the result is a blend of data and carefully directed imagination. So it's no surprise that faults can elude detection until they rip apart in an earthquake. But in pure, simple physics you can't release energy within a solid body except along a planar surface of some kind. Unless you have an explosion, of course, but they have a very distinct seismic signature. About maps of faults, only California (that I know of) requires active faults to be mapped, which it's been doing since the 1970s under the Alquist-Priolo law. Those are online at <http://www.quake.ca.gov/gmaps/ap/ap_maps.htm> I'd love to know if other states do anything similar. Peter: Iceland is very different; it sits right on the spreading line in the center of the Atlantic. It's the opposite of a subduction zone. There are two theories on why it's so volcanically prolific. One is that there's some sort of really deep source of fresh magma that comes up in a "plume"; that's the hotspot theory. The other is that a large piece of unusually "fertile" (that is, lava-yielding) rock is sitting there where subduction left it long ago. Hotspots are the textbook consensus, but I subscribe to the alternative, as longtime About.com readers may know. I treated the subject most recently in a book review: <http://geology.about.com/od/bookreviews/fr/Plates-Vs-Plumes-By-Gillian- Foulger.htm>
Gary Greenberg (gberg) Wed 27 Apr 11 12:31
>with the scum (continents) drifting around and joining and splitting You calling my continent scum? But seriously, that is one wicked lucid explanation!
Andrew Alden (alden) Wed 27 Apr 11 13:00
Thanks, Gary. I guess the upshot of what I've been saying is that there are all kinds of earthquakes. They all result from some sort of stress being relieved. More precisely, they are strain being relieved. If you take a block of rubber and deform it, whether by stretching or squeezing or twisting it, that deformation is strain. The strain can be relieved elastically (if you let it spring back) or plastically (if it somehow settles into that deformed shape permanently) or brittlely (if it ruptures). Rock is the same way; everything is at least a little bit elastic. We heard after the Japan earthquake that the island of Honshu moved several meters east. What really happened was that Honshu had built up strain, just like the rubber block, as the Pacific plate moved against it over the centuries. The quake was the result of a rupture between the Pacific plate, which is trying to move west as it's being pulled down by subduction, and Honshu. That was brittle failure. Parts of that fault between the two plates surely had plastic deformation too; that's what we see in faults that have been exposed on the surface. And usually there's some elastic strain left over afterwards. Anyway, Honshu didn't move several meters east so much as it rebounded several meters east.
Mark McDonough (mcdee) Wed 27 Apr 11 14:04
OK, I have a bit of a trivia question for you - except the effects on history were large. The city of Lisbon, Portugal was virtually destroyed by earthquake, fire, and tsunami in 1755. This basically ended Portugal's reign as a great power and some say set off a wave of skepticism about the concept of a just and loving God, accelerating the Enlightenment. Be that as it may, why Lisbon? I just don't think of the Iberian peninsula as earthquake country.
Peter Meuleners (pjm) Wed 27 Apr 11 14:07
As an addendum to that, aren't the Azores are known for undersea slides?
David Gans (tnf) Wed 27 Apr 11 14:12
> in pure, simple physics you can't release energy within a solid body except > along a planar surface of some kind. Curius about this, if it isn't too much of a digression.
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