(ORDO NEWS) — We are learning more about earthquake triggers all the time, but scientists still have a lot to learn about how seismic shifts actually work. Geologists think they have finally identified the key mechanism behind some of the most powerful earthquakes on the planet.
Researchers have found in tens of kilometers under the surface of the planet a possible factor provoking “mega-earthquakes”
The so-called “mega-earthquakes” or “super-earthquakes” occur in subduction zones where one tectonic plate goes under another. They are especially common in the Pacific and Indian Oceans and often lead to giant tsunamis.
New research suggests that the gradual, slow movement of rock deep beneath the subduction zone may be the key to understanding how these powerful tremors occur. Potentially, this discovery could improve forecasting models, which will make it possible to more accurately predict similar cataclysms in the future.
Researchers say that these so-called. Slow slip phenomena (SSE) do not occur in all subduction zones, but can significantly affect pressure build-up deep underground. Most importantly, they move energy in different directions during strong earthquakes and do not necessarily follow the movements of the plates themselves.
“Usually, when an earthquake occurs, we find that the movement is in the opposite direction to the movement of the plates, resulting in a kind of slip deficit,” explains geologist Kevin Furlong of Pennsylvania State University. According to him, slow earthquakes are characterized by a vertical downward movement in the direction of gravity, and not in the direction of plate movement. ”
Using high-resolution GPS data, Furlong and his colleagues analyzed movements along the Cascadia subduction zone (stretching from Vancouver Island in Canada to northern California) for several years.
A magnitude 9 earthquake struck Cascadia in 1700, and since then SSEs have been occurring well below the subduction zone, moving short distances at a slow speed. They look like a “swarm of events,” the researchers say, and the pattern matches similar data from New Zealand.
The researchers believe that although SSEs occur many kilometers below the surface, their movement can influence both the timing and behavior of earthquakes. These smaller events occur every one or two years, but they can cause something much more serious.
SSEs were first discovered by geologists about 20 years ago, and only recently have GPS instruments been sensitive enough to record their movements in detail – in this case 35 kilometers underground.
The results of the new study, which the researchers described as “rather unexpected”, will help shape future earthquake models. It is possible, for example, that some of the stress from plate movement in subduction zones is relieved by SSE deep underground. Moreover, knowing the direction of the forces that will release future earthquakes is critical in planning them. These natural disasters can be very unpredictable, so any information that can be gathered in advance is invaluable.
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