Earthquake Folksonomy

There’s something humbly communitarian about being outside on a crowded street corner when everyone turns to the person next to them to ask “hey, did you feel that?”. Perpetually oblivious, I only felt the earthquake because the guy standing next to me at the intersection pointed it out. I was grateful to him for alerting me, and we shared a little moment when the shaking stopped. He was keen on describing the ground motion – “It was a swivel, wasn’t it? It swivelled!” – while I tried to estimate epicentral distance and magnitude based on S wave / surface wave arrival times.

My estimates were a little off, though I got the magnitude more or less right (not by using special seismologist tricks, though, just pure small earthquake shaking experience available to anyone who’s lived here long enough). However, I seemed to be the only one who cared; the non-seismologists around me were playing some magnitude guessing games, but they were primarily interested in their own excitement, and describing how it felt to them.

A survey of local news coverage confirms that my initial questions really are different from the general population’s. The stories are littered with man-on-the-street quotes: the city manager of Lafayette (the city nearest the epicenter) said “it didn’t feel like a shake to me, it felt like a jolt”; a restaurant host said “at first it was kind of jolty, then it shook side to side; it felt like it was vibrating beneath you”; and the SF Chronicle reporters used their authorial voice to describe things as a “jolt and rocking motion”. Needless to say, the distinction between a “shake” and a “jolt” has not been given a precise meaning by the scientific community.

Once, I was stuck on a city bus in a Seattle traffic jam. I told the woman sitting beside me that I was a geophysicist, and she spent the next hour telling stories about her girlhood in Anchorage. She survived the 1964 Great Alaska earthquake by running in switchbacks up the walls of a ditch, which collapsed shortly after she escaped to flatter ground. She divided earthquakes into “crackers” and “rollers”, and was disappointed when I said that this distinction likely did not indicate anything special about the earthquake itself.

Earthquakes, you see, are pretty much all the same. They release the same basic kinds of seismic waves, in more or less the same proportions; bigger quakes last longer, but it’s only the really big ones that develop perceptible individual personalities. If you could graph the energy released by an earthquake directly on a seismogram, it would look like a simple spike or trapezoid. Two things conspire to make actual data much more complicated than that:

  • Earthquakes release seismic waves in a particular butterfly-shaped geometrical pattern. The same basic pattern is shared by almost all earthquakes, but you can be located in any position north, south, east, or west with respect to this pattern, and the butterfly can be oriented in any direction relative to the Earth’s surface. In fact, if you ask a seismologist to tell you about the basic kinds of earthquakes, she’ll probably describe the different ways this butterfly pattern can be oriented with respect to the ground.
  • All kinds of wacky geologic structure exists between you and the earthquake. As the seismic waves pass through this structure, they are bounced around and jumbled up.

I made up for trashing the woman’s ontology by telling her that the rolling motion of an earthquake is caused by Rayleigh waves.

The woman on the bus, and the folks quoted in the press today, have engaged in a sort of amateur human seismometry that isn’t scientifically useful but is definitely based on careful observation of the natural world. So far, I haven’t met any amateur human seismometers who’ve gone so far as formulating and testing a proper hypothesis, but nearly everyone on the West Coast has a story to share or a question to ask when I tell them I’m a student of earthquakes. (I’ve learned to summarize the tectonophysics side of my work in the most technical language possible when I’m not feeling chatty; usually it makes people stop asking questions.)

People living in seismically active areas have built up a tremendous amount of folk wisdom and curiosity about earthquakes, but it’s not connected to modern seismology or the scientific method. As a scientist I am often tempted to nitpick all the things such homebrew theories get wrong, rather than the good observations they are attempting to fit into a weird or woo-woo framework, but this approach tends to shut people down, rather than draw them out. Boo hiss!

It’s easier said than done, but the proper way to do outreach is to ruthlessly exploit people’s natural tendency towards curiosity and observation, and not stomp on it when it gets the wrong answer.


  1. Lab Lemming wrote:

    Yami, people have been keenly observing the natural world for about 194,800 years before applying the scientific method to those observations. But if you want to try nudging them in that direction, try this:

    Look for corellations between observations and soil type, moisture content, and thickness. If you’re teaching this semester, you could even get a soil map of the East Bay, stick it on the chalk board, and ask your students where they were and what they felt.

    As for the swivel guy, it’s a pity you aren’t single anymore. Otherwise you could have looked him in the eye and told him the swivel sensation comes from the Love waves that he felt…

  2. yami wrote:

    Marital status be damned, someday I’m going to learn how to begin sentences with “Oh, baby…” without cracking up. Then I will be a nonstop Love wave cheesy double entendre machine!

    [insert link to article on Love waves in the Journal of Irreproducible Results here]

  3. gengar wrote:

    Well, you’re doing the right subject; geology has plenty of word to enlist in the cause of dodgy punning. cleavage, ejaculite, cummingtonite…

  4. bret wrote:

    Well, I wouldn’t be so dismissive of folk taxonomies. People classify things in ways that are useful to them. If their classifications aren’t useful to scientists, that’s not their problem.

    Laymen, I think, classify their -experiences-. Scientists try to find and classify the -cause- of the experience, because that’s more replicable. But it isn’t necessarily more relevant.

    For Alaska Woman, “crackers” knock Uncle Ned’s portrait off the wall, and “rollers” make the lamp fall over. Perhaps this distinction actually results from the geography between her and the epicenter, but why should she care? She’ll add a couple nails to the portrait and tack down the lamp, and now she’s handled “both” kinds.

    Similarly, surfers have developed a taxonomy of ocean waves. You can tell a surfer that all waves are the same phenomenon, and what they’re experiencing results from topography of the seabed, but that doesn’t change the fact that some waves give a great ride, some are dangerous, and so on.

    Evolution has even programmed folksonomies into our bodies. We see light between red and green as a distinct “yellow”, but light between green and blue just looks green or blue. We see dark red as a distinct “brown”, but dark green and dark blue just look dark. For a hungry caveman, being able to instantly distinguish between ripe fruit (yellow) and underripe (green), or a fresh carcass (bright blood) and an old one (dark blood), was more important than color perception that remained true to wavelength.

  5. tectonite wrote:

    I’m a structural geology who ends up talking a lot about earthquakes to undergrads in nonmajors courses, so I’ve got questions about how I could use this stuff in teaching, and comments about what I do right now.

    First, a question — that butterfly pattern. I’ve never taken a class from a real seismologist; I took geophysics from Norm Sleep, who is… well, he’s Norm, and very smart, but not a seismologist. I learned about seismology from some books, and from talking to seismologists, but there is an awful lot of fairly basic stuff that I don’t know. So… the butterfly pattern. Is this basically a cool, more intuitive way of explaining the double couple idea? Are you kind of talking about the beach ball diagrams, except that there is more to it than the first motion on a seismogram – the energy varies in other ways besides “pushing” vs “pulling”?

    And second, earthquake folksonomy in teaching. I went to grad school in California (and was made homeless by the Loma Prieta earthquake), but I’ve done all my teaching in less seismically active areas. So I’ve got earthquake stories, but my students don’t. (If I taught in California, though it might be really cool to try to come up with some kind of class project to test hypotheses based on students’ earthquake stories.) About ten years ago, I collected a whole bunch of Loma Prieta stories from people on the old ca.earthquakes Usenet newsgroup. Some of the stories have a lot of the kind of detail you describe. I use the stories to have students try to make a map of the Mercalli intensities for Loma Prieta. It doesn’t get into the fundamental mechanisms, but it does illustrate how perceptions of an earthquake can vary from place to place, and how damage can be different. (And it lets me talk a little about how building standards affect what kind of damage occurs, and about liquefaction, and about other things that influence damage — which are probably the most important things for the nonmajors to think about, particularly in the interdisciplinary class I’m teaching right now.)

  6. yami wrote:

    Yeah, the butterfly is just a double couple radiation pattern with antennae drawn in. It describes the spatial distribution of P/SV/SH energy – P wave energy is at a maximum where SH is at a minimum, and vice versa.

    Even in California, my students hadn’t felt enough earthquakes to have well-established ideas about them – at least, not that they told me about. The class wasn’t structured in a way that I had a good chance to ask, and I suspect there is a natural level of embarassment about giving the “wrong” answer, so that if you don’t ask, repeatedly, they’ll never tell you. We also did an exercise translating descriptions into MMI, which was great, though a few students refused to believe that there could possibly be right and wrong answers…

  7. Lab Lemming wrote:

    Do you reckon wrongophobia is more or less detrimental to teaching than apathy?

  8. yami wrote:

    Hrm… my first gut guess is that wrongophobia is worse, but I think that’s because I value the wrongophobic students more than the apathetic students, and that’s not something I can justify.

  9. Lab Lemming wrote:

    Earthquake folksonomy of this week:
    At least we don’t live in Sumatra.

    I suspect that wrongophobia is a contributing factor to apathy- for people with a high probability of being wrong, they would be hard to distinguish.

  10. mark wrote:

    The other day one of the bloggers commented on how the methods of the Theory of Intelligent Design Creationism was applied to determine that the rumbling from North Korea a little while back was from a nuclear test. You ever hear stuff like that?

  11. yami wrote:

    No, but that sounds hilarious. Where was it?

  12. Lab Lemming wrote:

    Hopefully not on a USGS website…

  13. mark wrote:

    There were a few comments about ID theory and the North Korean nuke test on Ed Brayton’s post, ID is not an alternative theory.

    The comments arose from a Discovery Institute podcast, wherein they made the claim.

  14. yami wrote:


    … I guess that’s what happens when you create a “theory” without defining your terms, though. You can always encompass exactly as much territory as is convenient.

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