A. Even 4.5 billion years after its formation from a cloud of cosmic dust, most of the earth remains semiliquid. Radioactive decay keeps adding heat to the planet's interior, so it slowly circulates, like a pot of very, very thick pudding over low heat. But the part of the pudding (or planet) exposed to the air cools off faster than heat can flow up from below. Result: A crust forms, stiffer and more brittle than the goo beneath.
The goo keeps circulating beneath the crust, pushing chunks of still crust around with it. Result: In some places, chunks grind past each other (as in Southern California) or even one under the other (as in the Pacific Northwest). These processes do not take place smoothly—try sliding one brick over another brick; multiply the effect by several billion. You get the idea.
Q. If seismologists can't predict quakes, what good are they?
A. If we didn't have seismologists, who would TV crews interview when they weren't showing pictures of piles of bricks? But seriously, seismologists can't predict quakes for the same reason you can't say exactly when that brick you were pushing in the last example would finally stop sticking to the brick beneath it and slip a little. You know it's going to slip sometime, but you can't say just when or how far it will move when it does—that depends on the fine structure of the two particular bricks you're using, and no two bricks are exactly alike.
However, the same vibrations that knock bricks off cornices and break windows also serve sort of like X-rays that disclose the way the planet's built below the surface. For seismologists, every earthquake's like one more snapshot of the invisible cracks and bulges beneath our feet. With enough of that information in hand, they can at least say where quakes are most likely to happen, and, roughly, how often and how severe they're going to be.
Q: Well, OK, but I was watching the news, and those UW scientists they interviewed didn't seem to be that sure about anything even after it happened: where the quake was, how big it was, if there'd be aftershocks.
A: Considering how much the state of Washington spends on earthquake monitoring and research, we're lucky they even knew that it happened. UW seismologists still have to work with equipment bought 30 years ago in the wake of the '65 quake, and the Legislature has repeatedly refused to consider investing in a more up-to-date system. The 20 state-of-the-art strong-ground-motion sensors that provided most of the information about quake severity in the Seattle area are loaners from the U.S. Geological Survey, and they wouldn't have been online yet if the UW's administration hadn't squeezed a few thousand bucks out of special discretionary funds to hire a scientist to install them.
Q. Isn't it amazing no one died? What were the chances of that?
A. The reason we got off relatively easy in 2001 was because our building codes were tightened in conformity with what was learned from the quake of 1965, a near twin to this one—another reason not to fire all the seismologists just yet.
Q. Why was the shaking so much worse in Pioneer Square and SoDo than it was, say, on Capitol Hill?
A. What you feel in a quake depends on what the ground you're standing on is made of. Solid, well-drained soils transmit the vibrations smoothly and evenly; waterlogged, miscellaneous fill like the stuff most of the waterfront's built on can shimmy like jelly on a plate, barely moving in one place, wobbling all over a hundred yards away, even dissolving into sandy soup if the shaking goes on long enough.
Q. Is it really best to get under a desk?
A. Depends on a lot of things, including the desk. The safest inside place to be in a quake is a spot where the building's fastened firmly together, like a door frame or stairwell, but under a desk is a fine spot, especially when there's a lot of people looking for shelter and not a lot of door frames. More important is where you don't want to be, which is near windows or bookcases, under shelves or light fixtures, etc. Once the shaking stops, outside is by far the best place to be for a while at least, unless your idea of being outside is crowding into a narrow alley between two five-story turn-of-the-century brick buildings with stucco cornices. This is not Outside; this is more like Stupid.
Q. What is the Richter scale and how does it work?
A. Mr. Richter was a pioneer seismologist. His scale was designed to put a numerical value on quakes of various intensities. The details are complex, but the basic idea is simple: Each successive number on the scale represents a 10 times greater energy release than the number before. There are zillions of quakes smaller than 3 that you don't even notice. The one last Wednesday was close to a thousand times more energetic than a 3.
Q. Can animals really feel them before people?
A. No. For every pet that acted weird the night before the quake, there was another more surprised and freaked out than you were. If animals were reliable predictors of earthquakes, seismologists would have labs full of Jack Russell terriers instead of seismographs.
Q. Is there a connection between earthquakes and volcanic eruptions?
A. Yes and no. Volcanic eruptions involve large quantities of molten rock moving through the earth, and that movement produces "earthquakes," though usually too small to feel. The molten rock is produced by the same subterranean pressures and strains that produce earthquakes; however, a big earthquake in Olympia does not increase the odds of a volcanic eruption at Mount St. Helens or vice versa.
Q. So is this quake about the worst we have to look forward to?
A. Sorry, but no. Despite their numerical size, Wednesday's quake and the other recent record holders of 1949 and 1965 had relatively mild effects because they occurred over just a small slippage area 60 miles away and 20 to 30 miles deep in the earth. The farther away the epicenter is, the more dissipated the shock wave by the time it gets to you.
The kind of quakes we really have to worry about are quite different animals. Off the Oregon and Washington coast, a chunk of Pacific seabed is cramming underneath North America at a modest pace of an inch or two a year. Trouble is, North America resists the process, so the strain builds up until, every 500 years or so, it gives way along a front hundreds of miles long. The last time one of these megasuckers hit was in January 1700. It caused landslides into every major body of water, drowned whole evergreen forests, inundated scores of miles of coastline, and generated tsunamis that cleared beachfronts of every living terrestrial thing up to 50 feet above the tidemark. This is "the big one" you hear about. It could happen tomorrow; it could wait another 500 years. But it is sure to happen—sure as tides and taxes.