The people of Sichuan are now paying the price for living in buildings constructed to withstand an earthquake roughly one-fifth as powerful as the one that hit on Monday.
“The seismic code for the area substantially underestimated the earthquake strength,” says Hong Hao, a civil engineer at the University of Western Australia in Perth.
China’s earthquake regulations class the south-western Chinese province as equivalent to a 7 on the Mercalli intensity scale, which uses historical information to assess risk of damage from earthquakes.
Intensity 7 on the scale means that there is a 10% risk of an earthquake occurring once in 50 years that will be powerful enough to make it difficult for a person to stand up, but cause only negligible damage to well-constructed buildings. Monday’s quake would be classified on the Mercalli scale as a 10 or 11.