Geological puzzle of the Sichuan quake solved

Quake blew up three rock barriers along the fault zone

Quake hearth in Sichuan © USGS / NEIC
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Sichuan's unusually strong earthquake in May 2008 was triggered by the unexpected fractures of three massive rock barriers along the Longmenshan fault zone, according to the latest findings. As Chinese geologists now report in "Nature Geoscience", comparable heavy quakes in this region are rare and can only be expected every 4, 000 years.

On May 12, 2008, in the Chinese province of Sichuan, 1, 550 kilometers southwest of Beijing, a magnitude 7.9 earthquake occurred. The earthquakes destroyed millions of buildings, triggered rockfalls and landslides and killed almost 80, 000 people. The consequences of the quake were also so serious because the quake stove was only shallow. The starting point was the Longmenshan fault zone on the northwestern edge of the Sichuan Basin.

Quake concentrated at three points

Exactly what happened in the underground earthquake and why the quake was so unusually strong for this region has now been investigated by Zheng-Kang Shen scientists from the Beijing-based Chinese Soil Dynamics Laboratory. Using GPS measurements and satellite image analysis, they found that ground movement was concentrated at three points in the fault zone.

Massive rock barriers blown up

At these points massive rock separated smaller faults from each other. Normally, such rock barriers prevent subsurface fractures from continuing over several faults. However, the Sichuan quake blew up three such barriers one after the other, triggering an abnormally large displacement and movement of the ground.

As the scientists report, the greatest damage and death occurred in places that were close to these blasted barriers. In her opinion, this is another indication that it was here that particularly strong vibrations were triggered. A small consolation for the inhabitants of the region: Researchers also found that such a case only occurs every 4, 000 years, as it did in May 2008. display

(Nature, 30.09.2009 - NPO)