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Oh, Great: Humans Can Cause Earthquakes

In May of last year, an earthquake in the southeast of Spain violently shook the region. In the aftermath of the event, which registered a 5.1 on the Richter scale, nine people died and dozens of others were injured. The event caught many residents off...

by Kerri Connolly
Oct 23 2012, 5:15pm

In May of last year, an earthquake in the southeast of Spain violently shook the region. In the aftermath of the event, which registered a 5.1 on the Richter scale, nine people died and dozens of others were injured. The event caught many residents off guard because, despite the area’s regular seismic activity, quakes big enough to be felt are pretty rare.

Also odd was the fact that the quake occurred at an unusually shallow depth. Taking these details into consideration, Dr. Pablo Gonzalez and his team at the University of Western Ontario examined the geological evidence to investigate if there might have been any human interference that might have triggered the quake.

Human activity — hydraulic fracking, in particular — has been known to trigger small quakes, in some instances. But nothing has ever been shown to induce a quake until now.

What Dr. Gonzalez and his team now assert is that drastic draining of underground water sources may have lead to geological instability. Since 1960, the water table in southeastern Spain has dropped more than 820 feet, causing some parts of the the ground surrounding Lorca to sink by up to 15 feet. And the reason why all that water is being used up? Irrigation.

Earthquakes are caused by stresses in the Earth’s crust. With the Lorca quake, Gonzalez believes that draining the groundwater so dramatically created instability in the earth throughout the area, and that energy which might otherwise have been released slowly over time was instead released at a much faster rate — and more violently.

The Canadian team’s findings are pretty significant, particularly for areas that depend on vast quantities of groundwater. In the U.S., we routinely tap into massive underground aquifers to irrigate crops, especially in the arid Midwest. One of the largest, the Ogallala acquifer, which stretches from the Dakotas to north Texas, has seen some startling depletion in recent years. Since 1940, water levels in the area served by the Ogallala have dropped by more than 100 feet.

We tend to regard the West Coast as the most earthquake-prone part of North America. Yet you just have to take a quick look at recent history to see that the west is definitely not the only locus of quakes. In 2011, a 5.8 quake rocked mid-Atlantic states, causing damage to a generally older and more inflexibly-built environment. The Washington Monument is still closed due to damage caused by the quake. And just last week a 4.0 quake rattled parts of Southern Maine, sending shockwaves throughout New England.

In fact, some of the most powerful earthquakes ever recorded in North America weren't even on the West Coast or a major faultline, but came from an interplate region (not at a plate boundary, where most quakes occur). During December 1811 and February 1812, a series of brutal quakes struck New Madrid, Missouri, causing massive damage to the fledgling region. The USGS estimate the events at 7.5 and 7.7 by modern standards. A similar event today in the Midwest would be catastrophic. Not only has the population skyrocketed, but infrastructure would be particularly vulnerable. The West Coast prepares for volatile geologic activity through seismic retrofitting and stringent building/engineering regulations, but the same standards don’t hold true for the rest of the country.

So dropping water tables could cause quakes. Good to know, but with the droughts we’ve had this year, it’s hard to tell what we might be able to do about it. Of course, if something bad happens, we can just blame it on the scientists.

Image of destruction in Lorca via Antonio Miñano
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