300-km aftershock zone formed after China quake: expert

June 26th, 2008 - 10:53 pm ICT by IANS  

Xinhua
Beijing, June 26 (Xinhua) A 300-km aftershock zone has been created following the devastating earthquake that hit southwestern China May 12, killing more than 80,000 people, an earthquake expert said Thursday. “More than 13,000 aftershocks have been monitored in the quake zone, with the strongest reaching 6.4 magnitude on the Richter scale. Aftershocks will still remain for quite a long time,” seismologist Zhang Peizhen said while briefing senior lawmakers on the cause of killer 8.0-magnitude quake.

He was speaking at the third session of the Standing Committee of the National People’s Congress, the only legislative body of China.

Zhang, who is the president of the Institute of Geology of the China Earthquake Administration (CEA), said the aftershock zone of about 300 km was formed at the Longmen fracture, which links the counties at the quake epicentre - Wenchuan and Beichuan in Sichuan province.

He said after the quake, the CEA immediately sent a team of more than 500 specialists to the zone to evaluate the losses and conduct geological surveys. Studies showed that the quake was the faulting result of the Longmen fracture, lasting from Yingxiu township of Wenchuan to Beichuan county.

Longmenshan Mountains, are a mountain range in Sichuan province in southwestern China.

“During the more than one minute of shaking, a rupture of more than 60 km occurred in Guanxian and Jiangyou counties, a bordering area between Longmen Mountain and the Chengdu Plain,” said Zhang, who heads the expert committee investigating the cause of the quake.

He said ridge-lines, rivers and construction were destroyed by the surface rupture, which gave rise to a large number of geological disasters such as landslides and mud-rock flows.

The experts also said a global positioning satellite (GPS) system showed the quake caused a massive surface deformation.

“The Sichuan Basin has relatively descended, with Anxian and Dujiangyan sinking about 30-60 centimetres. Areas around Chongqing Municipality goes up about several millimetres,” he said, adding the deformation was only temporary, and with time passing by, the earth would be back to a stable movement state.

The expert said according to the GPS monitoring data, the gliding speed of the fault line suddenly slowed at the Longmen Mountains that enabled energy to be accumulated here so that a 8.0-magnitude quake was formed.

“It’s estimated that massive quakes would recur at least every 3,000 to 5,000 years. That’s why thousands of years of historical records did not register any massive quake on the fault line of the Longmen Mountain,” he said.

“The unpredictable and devastating May 12 quake is a new type that deserved to be thoroughly studied,” Zhang said.
Xinhua

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