Phayul Bureau Report
Dharamsala, September 13 – Researchers have found that geological stress has significantly increased on three major fault systems in the Sichuan region. The magnitude 7.9 quake on May 12 that struck Sichuan has brought several nearby faults closer to failure and could trigger another major earthquake in the region, say reports.
Geophysicists used computer models to calculate the changes in stress along the Xianshuihe, Kunlun, and Min Jiang faults – strike-slip faults like the San Andreas – which lie about 150 to 450 kilometers (90 to 280 miles) from the Longmen Shan rupture that caused the devastating quake..
The research team was led by Shinji Toda of the Geological Survey of Japan, and includes Jian Lin of the Woods Hole Oceanographic Institution (WHOI), Mustapha Meghraoui of the Institute of Geophysics in Strasbourg (France), and Ross Stein of the U.S. Geological Survey (USGS). Their findings were published September 9 in the online edition of the journal Geophysical Research Letters.
The team found that the May 12 event has doubled the probabilities of future earthquakes on these fault lines. Specifically, they estimated the probability of another earthquake of magnitude 6 or greater in the region is 57 to 71 percent over the next decade. There is an 8 to 12 percent chance of a quake larger than magnitude 7 in the next decade and 23-31 percent in the next 30 years.
“One great earthquake seems to make the next one more likely, not less,” said Stein, who has been collaborating with Lin and Toda for nearly two decades. “We tend to think of earthquakes as relieving stress on a fault. That may be true for the one that ruptured, but not for the adjacent faults.”
In 1999, a 7.4 magnitude earthquake in Izmit, Turkey, was followed four months later by an M7.1 event in nearby Duzce. The devastating December 2004 Sumatra earthquake (M9.2) and tsunami were followed by an M8.7 quake three months later.
“Because the Tibetan Plateau is one of the most seismically active regions in the world, we believe there is credible evidence for a new major quake in this region,” said Lin, a senior scientist in WHOI’s Department of Geology and Geophysics. “The research community cannot forecast the timing of earthquakes, and there are still significant uncertainties in our models. But the Turkey and Sumatra events indicate that one major earthquake can indeed promote another. Large aftershocks on August 1 and 5 in the Sichuan region may fit with this predicted pattern.
On May 12, 2008, about 300 kilometers of the Longmen Shan fault zone ruptured in an earthquake that killed at least 69,000 people and left another 5 million homeless. It was the deadliest and strongest earthquake to hit China since the 1976 Tangshan earthquake, which killed at least 240,000.
In addition to the broad prediction of earthquake triggering, the researchers have also forecasted the rate and distribution of seismic shocks greater than magnitude 6, a prediction that they plan to test from seismic stations over the next decade.
“The recent quake reminded us that Earth scientists have a tremendous responsibility to work on issues of societal relevance,” said Lin. “We don’t want to create panic, but there is legitimate cause for concern and we have a major role to play in educating the public about what we know.”
