The rapid movement of glaciers has also been shown to cause what are known as glacial earthquakes. Glacial earthquakes in Greenland peak in frequency in the summer months and have been steadily increasing over time, possibly in response to global warming.
Human Uses of Water and Induced Seismicity
In addition to climate-related impacts of water on seismicity, human management and applications of water can also affect earthquakes through a phenomenon known as induced seismicity.
For example, water stored in large dams has been linked to earthquake activity in various locations around the world, though the impact is localized in nature. In 1975, approximately eight years after Northern California’s Lake Oroville, the state’s second-largest human-built reservoir, was created behind the Oroville Dam, a series of earthquakes occurred nearby, the largest registering magnitude 5.7. Shortly after the water in the reservoir was drawn down to its lowest level since it was originally filled in order to repair intakes to the dam’s power plant and then refilled, the earthquakes occurred.
Several studies investigating the quakes concluded that fluctuations in the reservoir level, and corresponding changes in the weight of the reservoir, changed the stress loads on a local fault, triggering the quakes. Monitoring of earthquake activity at the reservoir in the years following the quakes established a seasonal correlation between the reservoir’s level and seismicity. Seismicity decreases as the reservoir fills in winter and spring, and the largest earthquakes tend to occur as the reservoir level falls in the summer and fall.
Induced seismicity can also occur when human water applications lubricate a fault. Studies by USGS and other institutions have linked sharp increases in earthquake activity in Oklahoma and other Midwest and Eastern U.S. states in recent years to increases in the practice of injecting wastewater into the ground during petroleum operations. Injection wells place fluids underground into porous geologic formations, where scientists believe they can sometimes enter buried faults that are ready to slip, changing the pore pressure on them and causing them to slip.
Getting the Big Picture of the Earth System’s Interconnectivity
Lundgren says when he first started studying earthquakes, everything was focused on understanding them within the context of plate tectonics and processes happening within Earth’s crust. But that’s now changing.
“In the past decade or so, with the widespread adoption of new technologies such as GPS that have greater spatial distribution and sensitivity, people have also begun looking at other second-order effects — other factors that might have an influence on earthquakes,” he said. “It’s very intriguing to be able to find potential links between earthquakes and climate, such as seasonal differences. The challenge, however, is squaring such connections with fundamental physics.
“We’re not close to being able to predict when an earthquake may occur as a result of climate processes,” he concluded. “Even if we know that some outside climate process is potentially affecting a fault system, since we don’t know the fault’s potential state of readiness to break, we can’t yet make that extra inference to say, ah ha, I might get a quake a week or a month later.”
What these studies do emphasize is the incredible complexity of our Earth system. Continued research will help us better unravel how its various components are interconnected, sometimes in surprising ways.
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