When we think about the earthquakeswe usually associate the phenomenon with plate tectonics. However, there are numerous other factors that can trigger seismic activity on Earth, including the melting of glaciers, an aspect of growing relevance. In recent decades, numerous studies have highlighted how the acceleration of melting of the polar ice capscaused by the heating globalcould be the basis of theincrease in frequency earthquakes, generally of low magnitude, in otherwise tectonically stable regions, such as Greenland. Such seismicity would be associated with the so-called post-glacial rebounda natural geological process which consists in uplift of the lithosphere following the loss of the overlying glacial mass and which plays a fundamental role in changing the stress regimes in the subsurface.
How Melting Ice Can Cause Earthquakes: The Isostatic Rebound Model
From a purely mechanical point of view, ice sheets represent a load on the Earth’s surface and, as such, exert a stress on the lithosphere which, in response, it deforms. About 20,000 years agoat the peak of the last ice age, beyond the 25% of the land areaas well as about 8% of the Earth’s surface, was covered by enormous expanses of ice, with thicknesses that in some places exceeded 3 km. In response to the loading of the glacial masses, the underlying lithosphere is slowly sunkin a phenomenon known as subsidence. This occurs because the lithospherethe Earth’s outermost rigid shell, rests on theasthenospherea portion of the coat that a behavior ductile–viscous.
To fully understand the process, imagine hypothetically filling an air mattress with honey and standing on it. At first nothing will happen, but as the seconds and minutes pass, you will slowly begin to sink and the mattress will buckle beneath you.
However, once you get off the air mattress, it will slowly return to its original shape. This reverse process is known as isostatic rebound or post-glacial rebound and occurs during and following the loss of mass of glacierscaused by their fusion. Basically, the crust rises again until it returns to its original equilibrium position. This is what happened starting from 19,000 years agowhen, at the end of the glacial peak, the ice caps have started to slowly melt. It is a process that continues today, especially in areas where continental ice sheets are still present, such as in Greenland And Antarctica.
It should be emphasized that the subsidence associated with the formation of ice sheets is not an instantaneous phenomenon, but is completed over the course of thousands of years. Similarly, isostatic rebound is a very slow process that can be completed even several hundred thousand years after the disappearance of the ice sheets.
But can these phenomena trigger earthquakes? According to numerous studies, the answer is yes. Especially during post-glacial periods, the reduction of the lithostatic load and the variations of the forces acting on the lithosphere can induce the development of new faults or cause the reactivation of pre-existing fractures, thus increasing local seismicity.
Earthquakes Triggered by Melting Ice Sheets: The Arctic Data
Driven by global warming, over the past 20 years, the Antarctic and Greenland ice sheets have lost an average of 150 billion And 270 billion tons of ice per yearThe loss of glacial mass was accompanied by an uplift of the lithosphere.
A study published in 2012 in the journal Geophysical Journal International estimated a maximum post-glacial rebound velocity greater than 20 mm per year in some areas of Greenland. Subsequent studies have found that low-magnitude earthquakes, generally less than 3 degrees, recorded in the last 30 years, often occur in areas of greatest isostatic uplift and in areas where the ice has completely melted or is in the process of melting, suggesting a possible correlation between the two phenomena.
Similarly, the glacial field Glacier Bayin the’Southern Alaskahas lost over 3000 km³ of ice since 1770corresponding to a decrease of about 1.5 km in thickness of the ice sheet. In some areas, peaks of uplift of up to 4 cm per year. A study of the 2008 conducted by researchers from NASA and the Alaska Earthquake Information Centre has highlighted how the massive melting of glaciers in the region may have been behind theincrease in the frequency of shallow earthquakes, with a maximum magnitude not exceeding 2.4 on the Richter scale, between 2002 and 2006. Similarly, several earthquakes of magnitude greater than 0.1, recorded between 1973 and 2001 in the glacier region Beringin southern Alaska, are attributable to the melting of the glacier itself. A more recent study, published in the journal Solid Earthsuggested a link between the isostatic adjustment and an earthquake of significantly higher magnitude, equal to 7.8 on the Richter scale, which struck southeast Alaska in 1958.
Other studies suggest a possible link between the melting of glaciers and the reactivation of paleofaults in Alpsin the United States (Michigan and Indiana) and in Scandinavia several thousand years ago.
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