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.