Joel Achenbach tells us just how much we don’t know about earthquakes:

Many scientists were caught by surprise by the magnitude of the China earthquake, estimated at 7.9 by U.S. scientists. Sichuan province has a history of earthquakes, but none so devastating. It was not near the top of anyone’s list of the most likely locations for a great quake. The data from satellites, which can track the motion of vast plates of the Earth’s crust, suggested a relatively moderate amount of strain building up in the rugged mountain front along the edge of the Sichuan basin.

“The lesson that one gets from this Sichuan earthquake is that we don’t yet fully understand where all the hazard is,” said Eric Kirby, a Penn State geologist who has extensively studied faults in that part of China. “We knew this was an active mountain belt, but we didn’t quite realize what it was capable of.”
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[USGS geophysicist Kenneth] Hudnut and his colleagues say they believe, based on preliminary data, that at least three different faults ruptured in succession. Rarely has such a cascading event been documented.

“Now that we see the cascading behavior, we get even more nervous. We see the potential here” in the Los Angeles area “for an earthquake that’s larger than what we thought it was capable of. We could get our comeuppance from Mother Nature any day here,” Hudnut said.

James Dolan, a University of Southern California geologist, has put together a map that shows faults in the Los Angeles area butting up against one another like passengers on a subway at rush hour. “Some of these faults could link up in ways we had never anticipated, which could lead to larger events,” Dolan said.

There is, as always, far more going on in nature than we give it credit for, while urbanization and development in America and elsewhere in the world are predicated on nature being relatively stable and quiescent. There hasn’t been a major earthquake in the center of a large U.S. city in a century. In that time, urban areas have become vastly larger and more built up, and the systems that make them run several orders of magnitude more complex. In other words, the true level of exposure/vulnerability here is quite high and continuing to rise, yet not meaningfully factored into our society’s decision-making. Add to this the potential for the kind of mega-quake the Post article mentions, and you have a potential outcome we really ought to work harder on mitigating with whatever limited tools are at our disposal.

Update: More here.