Was the quake in China an isolated case?
New model helps to determine the risk for successor issuesRead out
The earthquake that devastated the Sichuan province of Sichuan Province on May 12, 2008, was the first in the region since history began. With a magnitude of 7.9, his strength was also completely unexpected. But was it an isolated case? Or could the quake have changed the tension in the ground so that further heavy earthquakes threaten?
Major earthquakes like that in China in May 2008 are often followed by one or more quakes of almost the same magnitude. Thus, in 1999, shortly after the earthquake of Duzce in Turkey, the Izmit earthquake arose. In 2004, the magnitude 9.2 earthquake in the Sumatran quake was followed by a magnitude 8.7 quake in the same region.
Why this is so and what factors play a role has now been studied in detail by a team of geoscientists from the US Geological Survey, and the University of California at Santa Barbara. Her study has appeared in the current issue of the journal Nature. "A triggered earthquake after a major earthquake can occur months, years, or decades later, " explains Eric Kirby, a professor of Earth Sciences at Pennsylvania State University. "Sumatra is a good example, and Turkey's historical records show a series of earthquakes that are slowly progressing from east to west over the last 60 years."
Friction and tensions modeled
The researchers used a model of the Sichuan quake for their study. The earthquake occurred in an area on the eastern edge of the Tibetan Plateau, which was marked by the collision of the Indian and Asian slabs and was criss-crossed by geological turmoil. The new model shows the physical characteristics of the affected Beichuan Fault and the changes caused by the quake.
As a data source, however, the researchers could only resort to accurate data in part because the Chinese government is currently pursuing a very restrictive information policy. Friction force data margins were therefore used as a basis to fully capture the sometimes unknown or unexpected changes in friction caused by the movement of the perturbations. "We knew the fault was there and it was active, " explains Kirby. "I had worked in the region before, but I do not think anybody could have foreseen the size of this earthquake." Display
Tensions in the underground still big
According to the results of the modeling, after the quake on May 12, the tension intensified in some faults parallel to and perpendicular to the Beichuan Trench. Some minor faults south of the quake show, however, a relaxation. However, the majority of geological disturbances in this region are still under high pressure.
"The model includes what we know about the dislocations in the region and asks what tensions the earthquake has changed here, " Kirby said. The model shows us where the risk of a potential fracture increases, but we still do not know the exact trigger points for these distortions. The analysis does not tell us: "There will be an earthquake", but only that the potential for a quake exists in some of these faults.
(Penn State, 08.07.2008 - NPO)