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Seismic Science: Is number of earthquakes on the rise?

Dr. Michael Blanpied
USGS Earthquake Hazards Program
Tuesday, March 9, 2010; 10:00 AM

Are the recent earthquakes in Haiti, Chile and Turkey a coincidence or a sign of increases seismic activity? Dr. Michael Blanpied, associate program coordinator for the USGS Earthquake Hazards Program, took your questions about the causes of the recent quakes, earthquake forecasting and more.

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Dr. Michael Blanpied: Good morning, this is Mike Blanpied. I am a geophysicist and have done earthquake work at the USGS since 1989 (just before the Loma Prieta "World Series" earthquake). Since 2003 I have served as Associate Coordinator of the USGS Earthquake Hazards Program, in Reston, VA. I'll be happy to answer your questions about earthquakes today!

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Vienna, VA: Is there any way to really tell if large quakes are increasing in frequency on a historic basis? I don't know how long records have been kept, but even if we can go back 500 yrs is that enough time given how old the earth is to say with any certainty?

Also, what has been the worst quake to strike near the DC area and how at risk are we?

Dr. Michael Blanpied: A lot of people wonder if the rate of earthquakes is increasing, but it does not appear to be. We have good statistics on the numbers of earthquakes going back years, decades and centuries. See a nice summary here:

http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php

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Native Californian: Are there REALLY more and/or stronger earthquakes and tsunamis lately, or are they just better reported than decades ago (especially the ones occurring in remote land areas or under-sea)?

Dr. Michael Blanpied: There are really three main reasons why we're seeing more news about deadly earthquakes. First is that the quality of reporting is much higher. Second is that we're able to record them better due to global digital seismic networks that report data in real time. Third is that more and more people live in quake-prone areas, so earthquakes are more likely to strike vulnerable populations than was the case decades ago.

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Woodbridge, Va.: I read once that one of the biggest quakes in the USA was actually near St. Louis or someplace in the middle of the country. Is that true? If so, what would cause something like that?

Dr. Michael Blanpied: Back in the winter of 1811-12 there was a series of large earthquakes near New Madrid, MO (near Memphis area) in the central US. We believe they had magnitudes in the 7 to 7.5 range, and that similar quakes have occurred in earlier centuries. They would be deadly quakes if they occurred today.

However, even bigger quakes have occurred at the plate boundaries along the west coast and Alaska. The biggest was magnitude 9.2 off Anchorage in 1964. In 1700 there was a Chile/Sumatra-style quake off Cascadia (northern California up to British Columbia) that spawned a big tsunami. And the California quakes of 1857 (LA) and 1906 (San Fran) were around 7.8 or 7.9.

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Planning ahead: What should countries be doing to prepare for possible earthquakes? It seems like Chile was much better prepared than Haiti, for example.

Dr. Michael Blanpied: Yes, Chile has modern building codes and their recent buildings use modern, earthquake-resistant engineering. So Chile is a good lesson in how to properly prepare for quakes.

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Reston, VA: Is it possible that the earthquakes are a chain reaction. Are the earthquakes shifting other tectonic plates and causes more earthquakes?

Miss Leniart's class, Hunters Woods Elementary

Dr. Michael Blanpied: Hello Hunters Woods!

Yes, a big earthquake does cause more earthquakes, at least in the same area. We call those "aftershocks" and there can be a lot of them, some of them large. There have been over 200 aftershocks of the Chile earthquake, above magnitude 5, and thousands of smaller ones.

It's harder to say whether a big earthquake affects the plates at larger distances. For example, we don't know whether there's a link between earthquakes in South America and ones in Japan or Taiwan. This is an area of active science research.

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Chappaqua, NY: What aspect of earthquake prediction can best be made given the tools at hand? Locale, strength, timing, etc.

Dr. Michael Blanpied: We can do a good job of predicting WHERE earthquakes will occur, how BIG they might be, and what EFFECTS they will likely have. In some cases we can do a good job of estimating the RATE at which they occur, averaged over long times (centuries, say). However, thus far the earth has not shown us any means by which to tell that an earthquake is about to occur, or that a fault is ready to snap. Therefore, we are not able to predict the TIME of an impending earthquake in a useful way.

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New York, NY: Do the movement in certain plates and fault lines offer a better way to predict where the next quake might happen ?

Dr. Michael Blanpied: Yes, our understanding of plate tectonics gives us extremely useful clues on why earthquakes occur where they do, and where earthquakes are likely.

For example, southern Haiti has not had many earthquakes in the past century, prior to January 12's magnitude 7 catastrophe. However, we recognize that there's a plate boundary that is shearing the islands of the Caribbean, and that a part of that boundary goes right past Port au Prince, so the danger was recognized.

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Reston, VA: Why can't we predict where the next earthquake will hit? If we can, what measures are being taken to mitigate the effects?

Dr. Michael Blanpied: Yes, we do that! One of the big products of USGS is a map showing the earthquake hazard in the United States, where it is highest, moderate and low. That information is used in building codes that set construction standards for buildings, so that the buildings will be life-safe. You can find links to these maps here:

http://earthquake.usgs.gov/hazards/

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Platteville, Colorado: I'm curious as to weather the polar ice cap melt has increased pressure o the earth's plates? Aslo, could the melt cause a change in certain gases and bacteria within the earth enough to cause an increase in seismic activity? Lastly, wondering if an increase in geomagnetic storms could have an effect on the movement of the earth's plates?

Dr. Michael Blanpied: Some researchers are exploring the idea that melting ice and sea-level rise is changing the weight bearing down on faults, such that they might be more prone to making earthquakes. So far as I have seen this is in the realm of research, and an effect has not been solidly demonstrated. The effects of melting glaciers on volcanoes is also being studied. I am not aware of any way in which geomagnetic storms could affect earthquakes, and they would certainly have no effect on plate movements, as those are driven by slow motions in the earth's deep mantle.

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Philadelphia, Pa.: As a layperson, it would be my guess that each time there is a shift, there is a recalibration in the pressure along the fault line. Might it be possible that some shifts actually make allow the shifting plates to be more stable than before whereas others increasing the instability?

Dr. Michael Blanpied: Good thinking. The fault slip that happens in an earthquake changes the stress acting on other faults in the area, and may influence how close they are to failure themselves. The biggest effect may be on the first fault itself: Parts of the fault immediately adjacent to the part that slipped may be brought closer to failure. In 1999 the deadly Izmit earthquake in Turkey was followed a short time later by the Duzje earthquake to the east along the same fault line, and we believe they were related through stress. When this is observed we refer to "earthquake triggering."

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New York, N..Y.: I recall reading years ago that the odds of an earthquake on the East Coast are far less than on the West Coast, but that an earthquake on the East Coast would be more devastating. Is this correct and would you please explain what this means?

Dr. Michael Blanpied: That is true. Our plate boundary runs up the west coast, but there are significant earthquake hazards in at least 39 of our states, affecting at least 75 million Americans. The problem with quakes in the central or eastern US is two-fold: Seismic waves travel farther in the colder, older crust under that part of the country, so the damage can be more widespread. And there are more older buildings that may be vulnerable to being shaken. It is wise to examine earthquake hazards everywhere in the US, and to make prudent decisions about when it makes sense to replace or shore up vulnerable buildings.

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Annapolis, Md.: This may be a stupid question, but it is a thought that has bothered me for some time, so I would appreciate hearing your response!

is there any possibility that oil drilling could contribute to the earthquakes? I assume that when oil is pulled out, something is put back in because otherwise there would be a void, which would eventually collapse on itself? Bu is that true? And is there a possibility that the replacement liquid does not have the same properties or stability as oil, leading to instabilities in the ground which could eventually create earthquakes?

Are there any other human actions that could be causing these earthquakes?

thank you for your time and your response!

Dr. Michael Blanpied: In fact that is an insightful question. Yes, oil drilling as well as other fluid-related activities in boreholes (e.g., geothermal production) can change the stress on faults in the area, and induce earthquakes, due to the extraction of fluids or the injection of fluids (water may be pumped in, for example). Most times those are small earthquakes directly around the production site, but occasionally they can be big enough to be felt, and earthquakes up to the magnitude 5 range have been created through fluid injection into boreholes. It is a subject of research whether it's possible for larger quakes to be induced.

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Portuguese-American: Historically, Portugal's Azores Islands have experienced a lot of seismological and volcanic activity. E.g., a 7.1 quake (comparable strength to Haiti's this year) struck Angra do Heroismo, Terceira, in 1980, but with only about 70 deaths and 400 injuries (far fewer than Haiti's casualties).

One of the ways the Azores coped in the aftermath was to get Angra's historic downtown declared a UNESCO World Heritage Site in 1983, which helped to restore and preserve the area, as well as attract tourists.

What are the prospects for some of the stricken part(s) of Haiti to follow the same path? Aren't some of those devastated areas also historically and culturally significant?

Dr. Michael Blanpied: It is certainly important that Haiti's recovery be done in a way that the country and its cities and residents are made more safe from earthquakes. Haiti has suffered large earthquakes in the past, and will do so again (same as all the islands of the Caribbean). We have the means to estimate the hazard and the smarts to design buildings to withstand those hazards--those things are never the problem. The problem comes down to money (Haiti has a lot of infrastructure to replace in safer style, and a lot of remaining unsafe buildings to either replace or strengthen), and the public and political will to attack the problem of earthquake safety amidst so many other challenges.

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Munich, Germany: According to my old geology textbook, one method of predicting earthquakes was recognizing nervous behavior in animals such as horses. Is there really a connection between animal behavior and earthquakes or has this been debunked?

If the frequency of earthquakes is increasing, isn't prediction becoming more important? Are there any new advances in this area or do we still rely on skittish horses?

Dr. Michael Blanpied: We'd all love to be able to predict earthquakes, and people have been hunting for prediction methods for decades and centuries. Unfortunately, no means has yet been found for identifying which faults are about to go 'bang,' and the earth has not revealed any reliable precursory signals that indicate a quake is about to happen. (Sometimes there are foreshocks, but there is nothing about a foreshock that distinguishes it from any other earthquake, so they're not very useful for prediction.) There has been a lot of study of animals and earthquakes, and far more anecdotal reports of weird animal behavior, but nobody has yet managed to demonstrate a link.

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Rochester, NY: Would it be possible to trigger an earthquake deliberately, for strategic or political or criminal purposes?

Dr. Michael Blanpied: Why, are you planning something....?

This idea is floated from time to time, but I'm not aware of anyone actually trying it. Triggering a tiny earthquake is easy (see above about oil production), but triggering an earthquake big enough to matter would be extremely difficult. For one thing, we can't tell which faults are SO ready to go that a nudge from man would start a big earthquake. (Wouldn't the James Bond villain be disappointed to go to all that trouble and only make a magnitude 4?) Second is that earthquakes start very deep--miles below the surface in general, depths to which we can only reach through huge, production-scale drilling operations. I can't even imagine what a production it would take to get a bomb 6 miles down into a fault!

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20814: I apologize for the ignorance of this question, but to my lay understanding, it seems like all of the last month's quakes have been in and around the pacific rim. Is there any common plate or lava lake to all of these quakes? And I grew up in southern California, where we always were in fear of the "big one," even though most of us knew that the "big one" would really come in a smattering of lots of "little ones." Would you say this is the case with the quake in Taiwan?

Dr. Michael Blanpied: The Pacific is ringed by plate boundaries, and those play host to some of the most frequent and dramatic earthquakes and volcanoes--the so-called "Ring of Fire." You can see this on the first map on our web site, http://earthquake.usgs.gov, which shows earthquakes in the past week. It is the relentless motion of the plates that is responsible for most of the earthquakes we see.

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Reston, VA: What are good online resources for finding out about earthquake information worldwide?

Dr. Michael Blanpied: Our web site, http://earthquake.usgs.gov, is your portal to earthquake information. That includes up-to-the-minute info on earthquakes that have just occurred, and a host of information about older quakes, related research, FAQs, engineering topics, educational resources, and more.

One of the most popular parts (of an already popular web site) is a feature called "Did you feel it?" whereby you can register your observations of a quake you just felt, and contribute to a map showing the distribution of shaking. It's linked off the home page, and off the 'event page' for every earthquake we've recorded.

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anecdotal reports of weird animal behavior: Don't those only occur less than 30 seconds before a quake strikes? (My mother used to claim that she'd notice that the birds stopped chirping). Still, not much warning time.

Dr. Michael Blanpied: In some cases animals react to the first-arriving seismic wave (the p wave) that typically causes a "thump" but no damage. The p wave can arrive seconds or even tens of seconds ahead of the more damaging S and surface waves.

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Somewhere in the middle of the country: Recent news reports stated that the New Madrid fault was not active any more and there may not be any huge earthquakes as a result. Is this accurate, no more major earthquakes in the middle of the country from the New Madrid fault?

Dr. Michael Blanpied: As I said, the central US suffered a series of huge earthquakes in the winter of 1811-12 (you'll be hearing a lot about this as the bicentennial approaches!). Geologist who have studied evidence for past earthquakes have shown that similar quakes have occurred several times in the past. The rate of moderate-sized earthquakes is quite high, and there is a considerable likelihood that a magnitude 6 earthquake will cause damage if it strikes near a city. Scientists are challenged to understand the root causes of earthquakes in the interior of tectonic plates, but there is no evidence that the central US has suddenly become safe just at the point that we gained the means to study it in detail. The prudent thing is to do our best to estimate the hazard, and prepare accordingly.

Dr. Michael Blanpied: We have a fact sheet that discusses these topics in more detail, and you might find it interesting and useful:

http://pubs.usgs.gov/fs/2009/3071/pdf/FS09-3071.pdf

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Hunters Woods Elementary, Reston, Va: 1. Is seismic activity on the rise? 2. Will there be a great quake in the USA anytime soon? 3. How would seismic activity be on the rise if tectonic plates are basically floating on the magma?

Dr. Michael Blanpied: Seismic activity, in general, isn't going up or down. We get a lot of big quakes every year, and occasionally those hit near population and cause damage--it's mostly a matter of chance.

There could be a big quake in the US any time, we can't tell in advance! It could be a minute from now, or next week, or next year, or later. We do know they're coming, just not when.

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Nicholasville, KY: Just for the sake of curiosity, what would be the result of worldwide quakes above 6 or 7 magnitude, all occurring simultaneously? Is there even such a possibility? Thank you.

Dr. Michael Blanpied: There's not much connection between faults in different parts of the world, so no, I don't see a way for a big outburst of quakes from unrelated faults. That certainly would be dramatic though, so perhaps we'll see it coming from Hollywood!

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Moodus, CT.: Are you familiar with the "Moodus Noises" which have been the subject of discussions going back to Native Americans. Many claimed the noises were just a legend until a few years ago someone concluded that the noises are occassional small earthquakes. I have never heard these noises. Is it possible for small earthquakes to make strange noises every so often, and, if so, what are the risks of the earthquake ever becoming more serious?

Dr. Michael Blanpied: I'm afraid I'm not an expert on Moodus noises, and this forum doesn't give me the time to become more knowledgeable in order to answer your question.

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Winchester: The Chile earthquake altered the speed of the Earth's rotation! Amazing! I do not appreciate that now I have 1.26 millisecond's less sleep at night.

Dr. Michael Blanpied: Yes, I saw that news report about calculations of how much the Chile earthquake altered the rotational dynamics of the earth. Similar stories came out in 2004 after the Sumatra quake. It's a scientific curiosity.

Changing the vertical distribution of weight (mass) of a spinning object changes how fast it spins--this is how ice skaters accelerate their spins by pulling in their arms. If you know the equation to use, you can even calculate how much you shorten the length of a day by climbing down a ladder! :-)

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Dr. Michael Blanpied: Thank you for all the excellent questions. I enjoyed chatting with you. Thanks to the Post and our host, Paul Williams, for the opportunity to spend time talking about earthquakes and earthquake science.

If you have further questions, please consult our web site, http://earthquake.usgs.gov.

To receive email or text bulletins about earthquakes that have just occurred, sign up for our Earthquake Information Service: https://sslearthquake.usgs.gov/ens/

And follow the "contact us" link to send a question about earthquakes, to be answered by a USGS earthquake expert.

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