Stones write earthquake story

What happens at depths where no drilling is enough

Model of damage to the crust in 10 to 15 km depth during large earthquakes. The damage due to the jerky displacement and redistribution can not be directly analyzed, as even the deepest holes do not reach the middle crust. Only shifts (mm / year) on the surface of the earth as a result of slow decay and damage mitigation at depth can be measured today using high resolution geodetic techniques (GPS, InSAR). © RUB
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Scientists have long considered that large earthquakes also have drastic consequences in the lower crust. In the hard-flowing rock, tensions build up faster than previously thought. In their structures and structures, Steine ​​document Earthquake history, which geologists at the Ruhr University Bochum want to use to be able to better isolate the processes during and after earthquakes in the future.

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Modern methods of geodesy make it possible today to detect shifts in the Earth's surface from millimeters to centimeters per year. Suitable models for material behavior could be used to infer the processes in depth. The researchers receive the necessary information from the "damage pattern" of rocks that were at depths of 10 to 20 kilometers at the time of an earthquake and today reach the earth's surface in mountains.

For example, by comparing the microstructures of naturally deformed and experimentally produced quartz under controlled conditions, the depth of the Earth's processes can be understood.

Earthquakes - understand and calculate a cycle

Earthquakes occur at fault zones, such as the "San Andreas Graben". Geoscientists' damage analyzes show that stresses within an earthquake in the brittle upper crust are redistributed within seconds to the underlying layers and degraded over months to centuries. display

At the same time, the fault is loaded again until it gives way again in the next earthquake and the process repeats itself. By capturing the mechanical state of such systems, researchers hope to be able to limit the earthquake risk for decades to come.

Simple model already in use

A first simple model derived from quartz is already in use for earthquake risk estimation at the plate boundary between the Pacific and Australian plates. The results show a good correspondence with the geodetic shift velocities at the Earth's surface in recent years - the aftermath of a large earthquake about 400 to 450 years ago. The researchers hope that a suitably refined model could also be used for earthquakes that occur in large distances that exceed the period of modern data acquisition.

(idw - Ruhr-University Bochum, 26.04.2007 - DLO)