Geologists will next year launch a study to assess the risk of landslides on natural slopes in the event of an earthquake. Studies of earthquakes elsewhere have indicated that a large quake in Hong Kong would be more likely to cause localised landslips than a large-scale avalanche, but no detailed study has been conducted. In April, the Civil Engineering and Development Department will launch a pilot 'seismic microzonation study' in the northwestern New Territories to assess potential effects of a magnitude 7 earthquake on the stability of natural slopes. The study will take place over three years and cost less than HK$10 million. Launched a year before a fresh phase of the government's landslip prevention programme is due to begin, it will draw on data from 300 earthquake-induced landslips around the world. A team also went to Sichuan to visit areas hit by the May 12 Wenchuan quake. 'Collapse of rocky slopes there was more serious than that of muddy ones. Also, consolidated slopes proved to be quite resistant to quakes,' chief geotechnical engineer Pun Wai-keung said. The study area covers diverse environments, including sedimentary and igneous rocks and landfill sites. The risk of a big earthquake striking Hong Kong is much lower than in other parts of China and in neighbouring countries such as Japan. Still, experts have estimated that an earthquake of magnitude 7 could strike the city about once in 400 years. Previous studies by the department have found that the city's man-made slopes and walls are strong enough to withstand magnitude 7 quakes, and that the slopes are more at risk from heavy rain than earth tremors. But there has never been a study of the effect on natural terrain or of how the local geology and topography may affect an earthquake's impact. The Geotechnical Engineering Office of the department, which has been carrying out earthquake studies since 1988, classifies the earthquake risk in Hong Kong and Guangdong as 'low to moderate'. Hong Kong's rocky terrain may also reduce the impact of earthquakes. Seismic waves are amplified when they reach loose material such as soil, said Ng Sai-leung, professor of geography at Chinese University.