Israel: Sea of Galilee earthquakes triggered by excessive water pumping
By Michael Price
One evening in September 2013, windows rattled and ceiling fans swayed in northeastern Israel as a small earthquake rumbled beneath the Sea of Galilee—the water Jesus is said to have walked on—also known as Lake Kinneret. Four more tremors struck over the next 4 days. Then, in July 2018, a dozen small earthquakes shook the same spot beneath the lake on a fault—the slip surface along which an earthquake ruptures.
Although far more powerful earthquakes have struck the Levant, swarms such as these are rare and mysterious. A new study suggests human activity is to blame. Pumping too much water from the region too quickly may have “unclamped the fault,” the authors argue. And, they add, Californians and others living above major faults better pay attention, lest a similar appetite for water trigger a far larger, more dangerous quake.
Researchers have long known that humans can cause earthquakes by injecting fluid into the ground—a technique used in hydraulic fracturing, or fracking, to break open rocks and release natural gas or petroleum. Pumping water into geothermal vents to generate steam for heating and electricity has also triggered temblors. But earthquakes set off by pumping fresh water out of underground aquifers haven’t received much attention, says study co-author Emily Brodsky, a seismologist at the University of California (UC), Santa Cruz. “This is not the first example of groundwater extraction triggering earthquakes, but it’s uncommon,” she says.
Injecting water into aquifers is thought to trigger earthquakes by increasing the water pressure in pores within the rocks, lubricating faults and allowing them to slip more easily. But how might removing groundwater trigger an earthquake swarm? In a paper published last week in Geophysical Research Letters, the authors suggest a model in which extracting groundwater reduces the gravitational load on a fault—lessening the forces that push rocks on either side of the fault together to keep it locked. “Pulling the water out allows the rocks to kind of relax away from one another, and therefore unclamps the fault,” Brodsky explains.
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