Continents weaker than expected

Weak zone 10 to 15 kilometers deep explains deformations

Continental Crust MMCD
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The continents never stand still: they roam on the surface of the earth, re-emerge on the mid-ocean ridges, are pulled down again in other places, or even break. But what causes the stability of a continent and thus the susceptibility to a break or a seismic event like an earthquake? This is exactly what Australian researchers have investigated and published in the journal Nature.

According to common doctrine, the rock strength of the continents initially increases to a depth of around 15 kilometers, but then decreases with increasing depth because the rock becomes hotter and eventually viscous. But this theory can not explain certain basic observations of geology and even seems to contradict them.

Klaus Regenauer-Lieb, Roberto F. Weinberg and Gideon Rosenbaum of the University of Western Australia now went deeper into the continental firmness. As a method they used so-called dynamic feedback effects. These are the reactions that the continental underground shows when strong forces are acting on it. They developed numerical models that describe the strength of the continents as a result of fundamental physical and natural feedback processes, some of which had previously been ignored.

Surprisingly, it showed that the continents are considerably weaker than previously assumed. In what used to be the most stable area down to 15 kilometers, the researchers discovered a narrow zone of weakness where the greatest deformation occurs under stress.

"These findings also explain the origin of the shallow zones of weakness known as detachment faults that develop at depths of ten to fifteen kilometers. They were not really understood before, "explains Regenauer-Lieb. "There were dynamic shifts in our models that are very close to the slow movements before and after real earthquakes." Such so-called "slow slip events" were also described for the recent Sumatra earthquake that triggered a tsunami. display

(CSIRO, 03.08.2006 - NPO)