Monday, April 26, 2010

Earthquakes, volcanoes, global warming, and bad science

The number of large earthquakes per year is not increasing


It seems like there have been a lot of big earthquakes this year.  Today another fairly large quake, magnitude 6.5, occurred off the coast of Taiwan.  Back in March, I blogged about the possible connections between the large earthquakes this year, the upshot being that it may be possible for one large earthquake to trigger another large earthquake, but it is nearly impossible to prove that any one giant earthquake was triggered by another, the exception being earthquakes on the same fault system.

But are there more earthquakes than normal this year?  Geologists keep answering with a resounding "NO!" but most lay people don't believe the geologists.  This seems silly, in that geologists who study earthquakes have saved millions of lives, perhaps in this year alone, by studying fault systems, earthquake probabilities, and building codes.  And it is EASY for anybody to check what the geologists are saying!

One of my friends, Prof. Eric Mamajek at the University of Rochester, looked into the US Geological Survey's archive of recorded earthquakes and made some plots that show virtually no change in the number of strong earthquakes (including the plot at the top of this post), and no correlation between the number of strong earthquakes and several measures of global warming (you'll see why in the next paragraph).  I then went one step further and added up the total energy released by moderate and larger earthquakes every year since 1990.  At first it looks like there may be a slight trend, but if you take out just two earthquakes, the Chilean earthquake of this year and the Indonesian earthquake of 2004, there is no noticeable trend.  Those two earthquakes were big, but the faults they are on had produced similar earthquakes before, just very rarely.  And these plots retain the aftershocks of those quakes.  I also corrected the 2010 data point to account for the fact that only 1/3 of the year has gone by, otherwise that point would be lower.  In short, both the number and energy of earthquakes has been essentially constant over the past 20 years.


But the blame for the perceived (and, again, imaginary) increase in earthquake activity has been spread far and wide.  One Iranian cleric blamed the immorality of women, and some people are blaming this on pseudo-science like the whole 2012 doomsday nonsense.  Most people correctly dismiss this sort of talk out of hand, realizing that it is nonsensical and comes out of the mouths of non-scientists.  But then along comes Alan Weissman, a best-selling author whose book "The World Without Us" explores what would happen to the world if humans suddenly vanished.  Weissman does research, and has scientific credibility.  Then he penned this opinion column that appeared on CNN blaming the earthquakes and Icelandic volcano eruption on global warming, implying that the melting of glaciers and subsequent redistribution of mass on Earth's surface results in the release of seismic energy.

Weissman's volcano and earthquake claims are loosely based in some good science, but they rapidly extrapolate into speculation that, frankly, has no strong scientific backing.   Geologists know that the weight of material on Earth's crust does deform the crust and upper mantle of the Earth, and that this deformation can lead to earthquakes.  Hawaii is a prime example.  Hawaii's volcanoes are massive accumulations of volcanic rock, and that weight is causing the Big Island of Hawaii to sink at a rate of a few inches per year.  Earthquakes related to that subsidence are quite common, such as the 2006 Big Island magnitude 6.7 earthquake that damaged several of the telescopes on Mauna Kea. 

Melting glaciers are also known to cause the Earth's crust to rise, a phenomenon known as post-glacial crustal rebound.  The northern US and Canada are both rising in elevation due to this rebound.  But this response is slow.  The rebound measured for North America is due to the melting of continental ice sheets that happened over 10,000 years ago.  There have been scientific arguments that this rebound can occur on rapid timescales, perhaps as short as 1,000 years in the case of Icelandic volcanoes.  But global warming due to human activity has happened on a much shorter timescale, the past 100 years.  At best, it is premature to blame this year's earthquakes (which, as I said, have released roughly the same amount of energy as normal) and the eruption of Iceland's Eyjafjallajökull volcano on global warming, and every aspect of my scientific training screams "there's no connection!"

Erroneous claims by people with scientific credibility, like Weissman, hurt science.  These claims give fuel to those voices that have vested interest in discrediting solid science.  And the availability of online databases gives all of us the tools we need to go and check claims.  Are the numbers of earthquakes higher this year than in the past?  You don't have to take my word for it, and you don't have to guess based on the news reports, you can look up the numbers yourself.  And the numbers are absolutely clear: there are no more strong earthquakes this year than in a typical year, and the total amount of energy released by earthquakes is also pretty much the same; this year's energy tally is high only because of a single earthquake, the monstrous Chilean earthquake (and that area of Chile has seen even larger  earthquakes in the past, so even the extra energy from that earthquake is not unheard of).  

2 comments:

  1. Excellent article.

    There are different kinds of volcanoes, there are different kinds of earthquakes, and there are different kinds of "triggers" for them.

    That is the focus of one competent scientist who predicted the eruption of the Eyjafjallajökull volcano, which has erupted in just that manner by just that trigger for aeons.

    Predicting an event is one confirmation of a hypothesis.

    Since volcanoes and earthquakes have different trigger mechanisms, one can't use an "allie samie" theory to deal with the differences.

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  2. What about the US quakes going on from Oklahoma eastward? Are these more normal than people in this lifetime might know? It also seems to me like places waiting around for their "big one" are starting to scratch it off their lists. Is this the case?

    BTW, great article and much appreciated. -John-E

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