Here's Why Chile's Latest Giant Earthquake Didn't Hurt Anyone

Just two days into 2011, almost a year after being ravaged by a massive earthquake, the nation of Chile again shook with the force of a 7.1 magnitude tremor. Unlike last year, however, this quake killed not a single person and left minimal damage (phone and power lines were down for a few hours). Haiti was outright crippled by a 7.0 quake in early 2010, and yet Chile is sitting pretty after an even more powerful natural disaster. How did that happen?

As with swimming pools, the difference is the depth. Next time you hear of an earthquake and are trying to assess the damage it will cause, don't just consider its Richter scale rating. Also important is whether the quake is shallow-focus or deep-focus. A shallow-focus earthquake, the most common kind, occurs when the tectonic shift's "hypocenter"—the subterranean spot at which the slip of an earthquake begins—is located within 70 kilometers of the earth's surface. (The "epicenter" of an earthquake is "simply the point on the Earth's surface directly above the hypocenter.) Conversely, deep-focus quakes are energy releases occurring several hundred kilometers underground. It's simple: The deeper the quake, the less shaking here on terra firma.

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"The bottom line is that even though Chile was enormous, it was not shallow, reducing the shaking on the surface," says Aaron Velasco, a professor of seismology at the University of Texas at El Paso. "This isn't always true, but it's pretty consistent."

As an example of a relatively smaller quake whose shallow hypocenter made it devastating, Velasco points to 1994's Northridge, California, tremor. Despite being smaller on the Richter scale than both Chile and Haiti's recent quakes—6.7—the Northridge shift still killed dozens and injured thousands of others. "The damage done in Northridge was the direct result of it being shallow and in the middle of Los Angeles," says Velasco, "even though California leads the country in earthquake preparedness."