New buildings reinforced for earthquakes

New buildings in all cities and counties will soon be required to be built to withstand earthquakes, a senior seismologist told China Daily in an exclusive interview. The expanded requirements will extend earthquake protection to the one-fifth of the mainland previously not mandated to do so, said senior seismologist Gao Mengtan with China Earthquake Administration. "It is the first time in half a century that China has put prevention of collapse at the core of its national seismic provisions for structures," said Gao, deputy chief of the agency's Institute of Geophysics. "It is also the first time such a compulsory standard will cover the entire mainland." The expanded requirements are part of a new national seismic zone map that will become the minimum requirements for the design and construction of buildings, said Du Wei, a division director of the China Earthquake Administration. China publishes a seismic zone map roughly every decade, and the new one is scheduled for release by June, Du said. Until the new standard was set, buildings in about 21 percent of China's land area, or 15 percent of all cities above county level, were not required to be designed with earthquakes in mind, Gao said. They lie mainly in the country's central and eastern areas, such as some districts in Hubei and Jiangxi provinces, where major tremors are considered unlikely to occur. "There aren't even earthquake agencies in those districts," he said. But with the accumulation of information gathered from the ever-improving national network of digital earthquake monitoring stations, subterranean exploration and earthquake safety evaluation, authorities have decided to change the situation. "In the 2012 seismic zone map, there will be no area on the mainland where structural fortification against earthquakes is not required," Gao said. The seismic map details what levels of seismic intensity different areas are prone to experience. Unlike the Richter scale, which measures the strength of an earthquake, seismic intensity - usually on a scale of 12 - measures the amount of shaking at the Earth's surface. So, for instance, during a magnitude-7 earthquake, seismic intensity may vary from place to place from 5 to 10 degrees. On the 2001 map, the area prone to earthquakes of seismic intensity 7 accounts for 49 percent of the mainland's total. That will expand to 58 percent on the 2012 map, according to Gao. Nearly all Chinese provinces, autonomous regions and municipalities have been rocked by earthquakes above magnitude 6, according to Gao. In the 2012 map, 18 percent of the mainland is required to have their structures engineered to resist quakes with seismic intensity above 8. In 2001, the percentage was 12, Gao said. The new seismic provisions stipulate that a building will be able to be repaired to its full function in the event of moderate ground shaking. It must be reinforced so as not to collapse during very rare, extreme ground shaking, Gao said. Structural collapses cause most earthquake injuries and deaths, and countries and regions with well-developed building codes can usually reduce casualties to a minimum, he said. "In Japan and the United States, where structures are better prepared for disasters, an earthquake up to magnitude 6 often wreaks no havoc to society," Gao said. However, a magnitude-5.7 tremor on Nov 26, 2005 in Jiujiang, Jiangxi province, led to the death of 13 people, and sent 400,000 residents to the streets, Gao said. Nearly 60 percent of the 660,000 people killed in earthquakes in China in the last century lived in rural areas, meaning it is extremely important to reinforce residential and public buildings in counties, he said. Wang Yayong, former director of the Institute of Earthquake Engineering under China Academy of Building Research, said he believed losses from earthquakes will be drastically reduced if the seismic provisions for structures are implemented throughout the country. "Of course the cost for building a house or high-rise will increase, but the increase will not be that much, especially compared with lives and other damage that will be spared," Wang said