Melting glaciers contribute to Alaska earthquakes

In 1958, a magnitude 7.8 earthquake triggered an earthquake in Lituya Bay in Southeast Alaska, triggering a tsunami that rose 1,700 feet up a mountainside before running out to sea.

Researchers now think the widespread loss of glacial ice in the region contributed to earthquake preparation.

In a recently published research paper, scientists at the Fairbanks Geophysical Institute at the University of Alaska found that ice loss near Glacier Bay National Park has changed the timing and location of earthquakes of magnitude 5.0 or more in the area over the past century. affected.

Scientists have known for decades that melting glaciers have caused earthquakes in otherwise tectonically stable regions, such as inland Canada and Scandinavia. In Alaska, this pattern was more difficult to detect, as earthquakes are common in the southern part of the state.

Alaska has some of the world’s largest glaciers, which can be thousands of feet thick and cover hundreds of square miles. The weight of the ice sinks the land beneath it, and when a glacier melts, the ground springs back like a sponge.

“There are two components to the rise,” said Chris Rollins, the lead author of the study who conducted the research while working at the Geophysical Institute. “There is what is called the ‘elastic effect’, which is when the Earth immediately springs back up after an ice mass is removed. Then there is the long-lasting effect of the mantle flowing back up under the freed space.”

In the study, researchers link the mantle’s growing movement to major earthquakes in Southeast Alaska, where glaciers have been melting for more than 200 years. More than 1,200 cubic miles of ice have been lost.

Southern Alaska is on the boundary between the continental North American plate and the Pacific plate. They grind past each other about two inches a year – about twice as fast as California’s San Andreas Fault – resulting in frequent earthquakes.

However, the disappearance of glaciers has also caused the land of Southeast Alaska to rise by about 1.5 inches per year.

Rollins had been running models of Earth’s motion and ice loss since 1770 and found a subtle but unmistakable correlation between earthquakes and Earth’s recovery.

When they combined their maps of ice loss and shear stress with 1920s seismic data, they found that most major earthquakes were related to the stress of long-lasting earthquakes.

Unexpectedly, the greatest amount of stress from ice loss occurred near the exact epicenter of the 1958 earthquake that triggered the Lituya Bay tsunami.

While glacial melting is not the direct cause of earthquakes, it likely modulates both the timing and severity of seismic events.

When the earth bounces back from the retreat of a glacier, it does as much as bread that rises in an oven and spreads in all directions. This effectively resolves strike-slip errors, such as the Fairweather in Southeast Alaska, and makes it easier for the two sides to slip past each other.

In the case of the 1958 earthquake, the post-glacial rebound caused the crust around the fault to twist in such a way that the tension near the epicenter also increased. Both this and the non-clamping effect brought the error closer to failure.

“Plate movement is the main cause of seismic activity, buoyancy and deformation in the area,” said Rollins. “But post-glacial rebound contributes, kind of like the de-icing on the cake. It makes red zone faults more likely to reach their voltage limit and slip in an earthquake.”