The May 12 earthquake toppled many buildings in Wenchuan, Beichuan, Mianzhu, Dujiangyan and Pengzhou in southwest China's Sichuan Province. Experts say that people should not be quick to attribute the building collapses to poor construction quality. Instead, they argue that the magnitude of the earthquake is the chief cause of destruction, but the public does not seem satisfied with this statement.
The intensity of the May 12 quake exceeded the recommended earthquake fortification standards in local building codes, also known as "seismic fortification criterion", said Huang Shimin, director of the Institute of Earthquake Engineering at the China Academy of Building Research.
As an earthquake expert, Huang has been investigating the disaster areas for several days.
The destructive power of the quake is the chief cause of building collapse and damage, but unqualified building design cannot be excluded, he said.
According to the Seismic Ground Motion Parameter Zonation Map of China, seismic fortification criterion of these quake-affected areas is set at 7 degrees. Although the State Seismological Bureau has not announced the earthquake's seismic intensity, significant building damage suggests the intensity surpassed the issued seismic fortification criterion.
China Youth Daily asked in a June 5 editorial, "Why is the degree of damage between buildings in disaster area different? Is there any direct link between destruction and poor quality?"
Geotechnical mechanics expert Zheng Yingren, who is also an academician of the Chinese Academy of Engineering, affirmed that the building collapses mainly resulted from the quake's seismic destruction power. He added that various factors such as seismic intensity, direction and seismic wave propagation patterns can cause differences in damage.
"We should seek the truth through scientific investigation," he said.
Wenchuan's 8.0-magnitude earthquake is the most severe in a century to hit Sichuan. After it hit the Yingxiu-Beichuan-Qingchuan crust, the fracture process lasted 100 seconds. Seismic intensity along this earthquake fault zone exceeded 10 degrees, which exerted a devastating effect on area buildings.
In recent years, buildings in Chengdu, the capital city of Sichuan Province, have been built in accordance with the seismic fortification criterion – 7 degrees. The urban area withstood the challenge presented by the 8.0-magnitude quake, but those places near the fault zone inevitably faced a lower survival rate.
When an earthquake hits, the seismic intensity does not only change with distance from the epicenter, but is also influenced by the direction and additive effect of seismic wave propagation and geological structure of the area, according to Zhu Jieshou, director of the Deep Geophysics Institute at the Chengdu University of Technology.
"There are still a lot of riddles about the earthquake for us to solve," Zhu said.