Severe earthquakes can result due to tectonic plates colliding with each other, according to scientists. The researchers also contend that severe damage can be caused by the subduction zone. At subduction zones, one tectonic plate pushes over the other. The earth's surface is laced with about 51,000 kilometers of subduction zones and the motion along the margins of the zones averages a slip of about two inches per year.
According to researchers, where the margins stick and then rip apart into earthquakes, displacements have been as much as 65 feet, over many hundreds of kilometers, in a matter of only a few minutes. The researchers, led by Christopher W. Fuller at Yale and the University of Washington, used computer simulations to determine how the upper plate deformed above a subduction zone fault.
Past research has shown that as a subducting plate slides beneath an upper plate, stress builds where the plates meet and stick, and the upper plate warp creates a wedge and a bowl-shaped depression, called a forearc basin. Beneath the sea, this basin fills with sediment that empties from nearby rivers. It appears that the most severe subduction zone earthquakes occur in areas where such sediment-filled basins are found.
When sediment is deposited on top of the overriding plate, it reinforced the edge of the plate and caused it to stick directly above where the earthquake would happen so that it no longer deformed internally. The researchers speculate that this allows the subduction zone to remain at rest for longer periods of time and thus to stick, making it more prone to earthquake events.
The researchers say their model could have implications for forecasting areas within a subduction zone where great earthquakes are the most likely to occur. But they said it is not applicable to every subduction zone because each has different characteristics.