University of Tübingen: Constant activity of small earthquakes makes mountains grow

From a human perspective, earthquakes are the most damaging natural disasters – over the past hundred years they have caused more than 200,000 deaths and enormous economic damage. Mega earthquakes with magnitude nine or higher on the Richter scale are considered to be a particular threat. However, the unimaginable energies that are released do not seem to have any influence on the uplift of mountains, as geoscientists from the University of Tübingen found in a study. The energy of small earthquakes that are constantly working in the background seems to be more important for landscape design: In the study areas of Chile and Japan, Professor Todd Ehlers and Dr. Andrea Madella (Department of Geology and Geodynamics) Parallels between their seismic activities and the pattern and course of mountain elevations.Nature Geoscience published.

Earthquakes usually occur in the areas of the earth where continental plates collide. For example, along the Chilean coast, the Nazca plate is pressed under the South American plate, compressing the latter and accumulating elastic energy over hundreds of years. “If this energy is discharged in a short time – often in less than a minute – it can lead to earthquakes or even mega-quakes with terrifying earth tremors,” says Todd Ehlers, “while the oceanic plate slides under the continental”.

In addition, a mountain range unfolds at the edge of the compressed plate – on the west coast of Peru and Chile it is the Andes, whose mountains reach a height of more than 6,900 meters. On the islands of Japan, where several continental plates collide, mountains form a large part of the land mass.

Surprising patterns
In the study, the researchers examined records of earthquakes of various strengths along the edge of the plate in Chile and Japan and compared them with the topography there, i.e. the shape and shape of the respective mountains. “When we removed the mega-earthquakes and their smaller aftershocks from our calculations, we found that there was a correspondence between the energy released from the slow permanent activity of smaller earthquakes and the folding of the coast,” reports Andrea Madella.

Such earthquakes, which mainly occur at depths of 30 to 60 kilometers, have a strength of four to five. “The connection surprised us. Obviously, these smaller earthquakes have so far been underestimated, ”says Ehlers. “They are constantly active in the background without any particular spatial or temporal peak values. It seems to be their collected powerful energy that makes the mountains grow over periods of millions of years. ”But what happens to the energy from the mega earthquakes? “It looks as if it could, so to speak, bend the whole landscape cyclically,” explains Madella. “But that recedes again, and there is often no permanent mountain elevation.”

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