A model 'to explain linkage between quakes and causes'

Scientists, including an Indian-origin researcher, have devised a numerical model which they claim would help explain linkage between earthquakes and the powerful forces that cause them.

Attreyee Ghosh and colleagues at Stony Brook University say their research focussed on the system of plates that float on Earth's fluid-like mantle which acts as a convection system on geologic time scales, carrying them and the continents that rest upon them.These plates bump and grind past one another, diverge from one another, or collide or sink (subduct) along the plate boundary zones of the world.

Collisions between the continents have produced spectacular mountain ranges and powerful earthquakes. But the constant stress to which the plates are subjected also results in earthquakes within the interior of those plates.

William E Holt, who led the team, said: "Predicting plate motions correctly, along with stresses within the plates, has been a challenge for global dynamic models.

"Accurate predictions of these is vitally important for understanding the forces responsible for the movement of plates, mountain building, rifting of continents, and strain accumulation released in earthquakes." 

The data for their global computer model came from Global Positioning System measurements, which track the movements of Earth's crust within the deforming plate boundary zones.

They compared output from their model with these measurements from Earth's surface. "These observations -- GPS, faults -- allow one to test the completeness of the model," Dr Holt said.

The team found that plate tectonics is an integrated system, driven by density variations found between the surface of Earth all the way to Earth's core-mantle boundary.

A surprising find was the variation in influence between relatively shallow features (topography and crustal thickness variations) and deeper large-scale mantle flow patterns that assist and, in some places, resist plate motions.

Ghosh and Holt also found that it is the large-scale mantle flow patterns, set up by the long history of sinking plates, that are important for influencing the stresses within, and motions of, the plates.

Topography also has a major influence on the plate tectonic system, according to the researchers who have published their findings in the 'Science' journal. 

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