How to (and how not to) talk about earthquake hazards in the media

A post by Chris RowanThere’s often a fine line to be walked when you’re asked to talk about future earthquake risks in the media. People are looking for what scientists can’t provide: firm predictions of where the next big earthquake is coming from, and when. Meanwhile scientists have to downplay the hiding-to-nothing that is the specific prediction game and communicate what we do know: the areas that are most at risk from large and damaging earthquakes, so that people and emergency planners are not taken by surprise when they inevitably occur – be it next month or next decade. It’s tricky: talk up the dangers too much, and you might spark an unneccesary panic. Don’t go far enough, and you store up trouble for the future in the form of an unaware and unprepared populace.

As an example of how to do it right, read this excellent article on the CNN website by USGS seismologist Susan Hough. You should read the whole thing, but here are some key quotes:

Pointing to any one corner of the Earth as the location of the next Big One is not a winning game. Take a map of the world’s most active plate boundaries and throw a dart; where it lands is as good a guess as any.

…the next Big One might not be within the lifetime of any individual alive today but is very likely to occur within the lifetime of many of the buildings being constructed today.

What we know for sure is that preparedness remains our best defense against devastating earthquakes.

It’s perhaps no surprise that this particular seismologist is so good at talking about earthquake risks and predictions: she is, after all, the author of an excellent and highly readable book on the subject. However, if you want demonstration of just how easily one can go astray in this particular field, Simon Winchester, the author of a number of popular geoscience books, provides one with this rather less good article in Newsweek. It’s unpromisingly titled ‘The Scariest Earthquake Is Yet to Come’, but since titles are the first casualty of the editor’s red pen, I’ll overlook that. But following a few paragraphs describing the March 11th Japanese earthquake and tsunami – the standard “we are all helpless against the caprice of Nature” angle – we get this:

For this event cannot be viewed in isolation. There was a horrifically destructive Pacific earthquake in New Zealand on Feb. 22, and an even more violent magnitude-8.8 event in Chile almost exactly a year before. All three phenomena involved more or less the same family of circum-Pacific fault lines and plate boundaries—and though there is still no hard scientific evidence to explain why, there is little doubt now that earthquakes do tend to occur in clusters: a significant event on one side of a major tectonic plate is often—not invariably, but often enough to be noticeable—followed some weeks or months later by another on the plate’s far side…Now there have been catastrophic events at three corners of the Pacific Plate—one in the northwest, on Friday; one in the southwest, last month; one in the southeast, last year.

That leaves just one corner unaffected—the northeast. And the fault line in the northeast of the Pacific Plate is the San Andreas Fault, underpinning the city of San Francisco.

This assertion is problematic in a number of ways. Firstly, putting the magnitude 6.3 Christchurch earthquake – even last year’s magnitude 7 – in the same class as the events in Chile and Japan is wrong. The Christchurch quake released thousands of times less energy than either of those events, and was only so damaging due to its close proximity to Christchurch.

Secondly, the idea that megaquakes may beget other megaquakes is still at the ‘interesting speculation’ stage. In other words, there is still no ‘hard scientific evidence’ that there’s an effect to explain at all. Even if there is, it’s considerably more complicated than ‘look to the opposite side of the plate!’: when you’re considering the far-field effect of megaquakes, the other side of the planet would be just as susceptible as the other side of the plate. The state of stress in the crust is a far more important factor than any particular relative location.

Thirdly, the San Andreas Fault is probably not physically capable of producing much more than a magnitude 8 earthquake. The reason subduction thrusts are the source of such large earthquakes is because of their shallow dip, which results in a large area of the fault being above the depth where rocks become too warm and weak to rupture brittlely in earthquakes. Because the San Andreas Fault is almost vertical, the area that can potentially rupture is smaller, and the upper limit on the size of earthquake it can produce is also smaller. An earthquake on the San Andreas, which is on land, also wouldn’t produce a tsunami, which was what caused the real damage in Japan.

This isn’t to say a magnitude 8 earthquake isn’t a very serious future hazard for California. But to argue that it would be more ‘scary’ than what we witnessed a couple of weeks ago is pushing it a bit. To argue that this horror is imminent is borderline irresponsible – there is no scientific basis for stating the risk of a ‘Big One’ in California is any greater than it was a month ago. The same is true of the arguably much more scary Cascadia subduction zone to the north – which can potentially produce a magnitude 9 earthquake, and will produce a tsnuami when it does so. We know that both of these faults will rupture at some point in the future, and people need to be aware of that. But claiming we’re in some period of extra-special risk right now is, to put it bluntly, just making stuff up.

In conclusion: Susan Hough: take a bow. Simon Winchester: don’t. In any sense of the word.

Categories: earthquakes, geohazards, public science, ranting
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Comments (15)

  1. Lockwood says:

    This lies at the heart of my distaste for Winchester: take what people know a little bit about, then sensationalize the dickens out of it. Don’t worry about the stuff they *ought* to know about (e.g. Cascadia vs. San Andreas), but likely don’t. Play up the big names. To me, too much of his work amounts to marketing, not informing.

  2. terry says:

    between this and supermoon/solar flares…it must be a very frustrating time for geoscientists.

    also avoid the comments on that CNN article.

  3. Garry Hayes says:

    Isn’t this all a government conspiracy and HAARP anyway? (wink, wink)

    Thanks for a good article and excellent rant!

  4. Erik says:

    Chris, maybe you can help me with this: In the idea that these earthquakes come in sets (not saying I believe it), it seems to assume that the Pacific Basin is one big plate. However, we know that the Chilean earthquake was on the Nazca plate and the Japanese on the Pacific. So my question is, do we have any idea how stresses from large earthquakes are transferred across divergent boundaries like the East Pacific Rise? That would seem to be the crux of any argument about one earthquake begetting another …

    • Chris Rowan says:

      I actually was going to mention the fact that the Pacific plate is not synonymous with the Pacific ocean, but the San Andreas is in fact the one place where the Pacific plate is in contact with the western coast of the Americas.

      But anyway, direct stress changes even due to mega-earthquakes are limited to a relatively small area around the rupture. Any far-field triggering would have to be due to the influence of seismic waves – in which case, as I said in the article above, whether you’re on the same plate or not would be relatively unimportant.

      • Erik says:

        I was picturing it more as a sort of “morphing blocks” model rather than thinking of the effect of the seismic waves themselves. Thanks for clarifying!

  5. Evan says:

    Does the subduction zone governing this earthquake present Episodic Tremor-Slip (ETS) symptoms, as seen with the Cascadia subduction zone?

  6. CherryBombSim says:

    My impression is that Newsweek’s science reporting is utterly atrocious. Not just in the details; they have people writing science articles who clearly are not familiar with science in general.

  7. Pam Harman says:

    Perhaps Winchester’s notions were not wrong, but his choice of plate was. There was a 6.8 quake in Myanmar this morning which look to me like it is at the other edge of the southern part of the Asia plate from the Sendai swarm(I am not sure if I have the names right, but looking at the USGS site, it appears that the other side of the plate has produced a quake)

    • Chris Rowan says:

      Again – if this earthquake is in in any way related to the one in Japan, it is not because it is on the opposite side of the same plate or due to any other geographical quirk.

      I would also point out that earthquakes of this size are not infrequent.

      • Pam Harman says:

        I am not trying to be disingenuous. I am not a geologist by training but I can hear your frustration in your response..

        From the little I remember of high school physics, one motion is going to have a counterbalancing motion elsewhere. I think I understand that this is the mechanism of an earthquake itself, but that assumes all the energy balances out in a localized fashion. I am questioning if that assumption needs to be re-explored.

        When I was growing up in the 1950′s we all looked at the map of Africa and South America and thought what a coincidence it was that they looked like pieces in a jig saw puzzle. Then came plate tectonics and it seemed that in a sense “we” were right.

        So, my probably ill formed question is whether a large amount of energy expended at one side of a solid plate could cause a reaction at the other margin . If not, is it because the plate intersections are different, one slides under another so that it is like fanning a deck of cards? Is the distance too far and the composition of the plate itself too heterogeneous to allow energy transfer? Is the fault line or plate boundary in Myanmar of a type similar to the San Andreas and the engineering /physics answer is the same for both ?

      • Maria says:

        Is the distance too far and the composition of the plate itself too heterogeneous to allow energy transfer?

        That’s pretty much it. Stress transfer within a plate isn’t appreciably more efficient than stress transfer over the same distance across plate boundaries.

  8. Todd Redding says:

    Simon Winchester was interviewed on CBC Radio in Canada yesterday, you can stream the audio here:

    http://www.cbc.ca/thecurrent/episode/2011/03/24/geological-disasters-simon-winchester/

  9. Lurking says:

    San Andreas.. eh. Okay. My concern would be the Cascadia SZ.

    But the one thing that sort of mucks this up, is the presence of aseismic action there. Is there a good source of info on these “slow quakes” and how much energy is released? Or, how they may or may not mitigate the potential for a future Sumatra or Japan style event?

    Links (3)
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