A 7.2 earthquake struck Pakistan on Wednesday morning. The earthquake occurred in a remote, southwestern part of the country, and—as of this writing—no injuries have been reported. Earthquakes always result in a flurry of questions to the Explainer’s e-mail inbox. To pre-empt that, we’ve rounded up a few questions and answers:
Can humans affect the frequency of earthquakes, just like we’ve affected the global climate?
Not significantly. While certain activities, like mining, oil extraction, and dam-building can trigger an earthquake by changing the weight on tectonic plates or lubricating the joints between them, there is no evidence that humans have caused a quake of greater than 5.3 in magnitude. Major earthquakes like the one in Haiti are natural and unstoppable events. If Earth’s plates are going to shift and cause one of these disasters, there is nothing we can do. [ Read more.]
What’s the best way to dig through rubble?
It often comes down to scooping up the rocks one by one. Sophisticated equipment and techniques are more useful in the initial stages, before potential survivors have been located. Construction vehicles like loaders and backhoes are sometimes employed in the first hours of the search, to move away the perimeter rubble in which people are rarely found. Then urban search-and-rescue teams use robots, cameras, and dogs to sort through rubble quickly and safely. However, once a survivor is located, the team generally ends up moving rocks by hand, since heavy machinery would pose a serious risk to the survivors buried underneath. [ Read more ]
Can an earthquake affect the way the planet spins on its axis?
Yep. As you’ll recall from science class, the rotating Earth resembles a spinning top: The planet’s axis does not always point in exactly the same direction but wobbles very slightly, describing small but measurable circles at the poles. A very large earthquake—one of a magnitude of 9.0 or greater—can shift enough mass relative to that of the entire Earth to alter, very minutely, the course of that wobble. But the planet’s speed of rotation (which, of course, determines the lengths of our days) remains unchanged, so we don’t need to worry about adjusting our watches. [ Read more.]
Is it possible for an aftershock to be as large as the main event?
By definition, no. If an earthquake is followed by a more powerful seismic event, it’s automatically redefined as a foreshock. The largest tremor is always classified as the earthquake; everything else is either a foreshock or an aftershock. It’s also highly unlikely that a quake as massive as the one in Sichuan in 2008, which registered a magnitude of 7.9 on the Richter scale, would be followed by an event of the same intensity—especially after so much time had elapsed. [ Read more.]
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