Multiple news stories have been released lately exposing the risk of earthquakes due to fracking. Now it seems that even simple irrigation could pose a threat to areas susceptible to sliding tectonic plates, namely the San Andreas Fault.
ABC News reported that the pumping of groundwater for agricultural irrigation in California is putting stress on the San Andreas fault line. Geologists have taken GPS readings of the area and discovered that portions of the San Joaquin Valley near the San Andreas Fault are steadily sinking from the depletion of the aquifer. Meanwhile, surrounding mountains are being raised up, which is the source of the stress on the fault. While the quakes might not be catastrophic, the stress could result in multiple small earthquakes in the area.
The lead researching geologist at Western Washington University, Colin Amos, told the Associated Press, "The magnitude of these stress changes is exceedingly small compared to the stresses relieved during a large earthquake."
The research findings about the San Andreas Fault were released in the journal Nature this Wednesday. "These results suggest that human activity may give rise to a gradual increase in the rate of earthquake occurrence," the study said, according to the Los Angeles Times.
The human activity, in this case, is the removal of groundwater for irrigation around the San Andreas Fault. "It reduces the forces that are keeping the fault clamped together - leading to more small earthquakes during dry periods of time," Amos explained to The Associated Press. "During wet periods of time when the fault is loaded down, the forces that are keeping the fault clamped down are greater. It inhibits the sliding of the fault." In other words, the heavy groundwater weighs down on the Earth, keeping the San Andreas Fault from shifting, but when the groundwater is removed the land is lifted, resulting in small local earthquakes.
According to Nature World News, the San Andreas Fault runs roughly 800 miles through western California to form a portion of the rift between the Pacific and North American tectonic plates. While a large earthquake on the San Andreas Fault has the potential to kill 1,800 people, the magnitude of earthquakes from groundwater extraction would be comparably smaller.
Headlines & Global News reported that the Central valley loses enough water through irrigation to fill up Lake Tahoe, which could result in a drought and even more depleted groundwater. Amos seems to believe the damage from the irrigation practices has already been done, adding, "These earthquakes are likely to occur no matter what humans do... Human activities are changing things that we hadn't appreciated before - it's a wake up call."
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