May 12, 2008

experts comment on the earthquake in China

The earthquake measured 7.8 on the Richter scale, making it one of the most powerful to hit the region for the last century, and left tens of thousands of people dead or homeless.

Dr David Rothery, Earth Scientist at the Open University, said:

“Today’s magnitude 7.8 earthquake appears to be a result of the continental collision of India with Asia, which is forcing the Tibetan plateau towards the east over the Sichuan Basin. The focus was at a relatively shallow depth of about 10 kilometres, which may account for the strong ground motion and the extent of the damage and loss of life. A nearby magnitude 7.5 earthquake in August 25, 1933, killed more than 9,300 people.”

Professor Bill McGuire, Benfield Hazard Research Centre at University College London, said:

“The Sichuan Basin of SW China is an area of high seismicity, as demonstrated by a big quake in 1933 which took close to 10,000 lives. The area is now far more densely populated and urbanised but the large and growing death toll suggests that little attention has been paid to ensuring that new buildings are sufficiently earthquake-proof.”

Dr Brian Baptie, Seismologist at the British Geological Survey, said:

“Latest reports suggest between 3,000 and 5,000 people have been killed by a magnitude 7.8 earthquake in the south-western Chinese province in Sichuan. The earthquake occurred 92 km northwest of the city of Chengdu in eastern Sichuan province and over 1500 km from Beijing, where it was also strongly felt. Earthquakes of this size have the potential to cause extensive damage and loss of life.

The epicentre was in the mountains of the Eastern Margin of Qing-Tibet Plateau at the northwest margin of the Sichuan Basin. The earthquake occurred as a result of motion on a northeast striking thrust fault that runs along the margin of the basin.
The seismicity of central and eastern Asia is caused by the northward movement of the India plate at a rate of 5cm/year and it’s collision with Eurasia, resulting in the uplift of the Himalaya and Tibetan plateau and associated earthquake activity. This deformation also results in the extrusion of crustal material from the high Tibetan Plateau in the west towards the Sichuan Basin and southeastern China.

China frequently suffers large and deadly earthquakes. In August 1933 a magnitude 7.5 earthquake struck near Diexi, about 90 km notheast of today’s earthquake. This destroyed the town of Diexi and surrounding villages, and caused many landslides, some of which dammed the rivers. Approximately 9,000 people are thought to have died.”

Dr John Whalley, Structural Geologist at University of Portsmouth, said:

“The Sichuan earthquake is a reminder that not all major earthquakes are directly related to the present day boundaries of the Earth’s tectonic plates. About 45 million years ago India began to collide with the southern margin of Asia but has continued to move northwards ever since by about 5 cm per year. The Himalayas and the Tibetan Plateau are the consequences of this continuing northwards push.
As well as creating these extensive high areas, India’s push also generates an eastwards spread of material away from the Tibetan plateau. In the Sichuan area the margins of the plateau are being pushed under weaker sedimentary rocks. It is along one of the faults marking the boundary of these sediments that today’s earthquake occurred.”

Dr Stephen Edwards, Earth Scientist, Benfield UCL Hazard Research Centre at University College London, said:

“The huge jump in the estimated death toll demonstrates the confusion that surrounds a big natural disaster, such as this earthquake in southwestern China. The event also highlights the problems of having large numbers of people concentrated in one area, because 900 children may have been crushed in a collapsed school. Once again this event exemplifies the need for better disaster preparedness”

Tom Foulkes, Director General of the Institute of Civil Engineers, said:

“An earthquake of this magnitude is likely to severely damage much of the area’s infrastructure, including buildings, homes and essential utilities systems, posing a grave threat to the local population. Of particular concern in this area of China is the proximity of the Three Gorges Dam, though thankfully it seems not have been damaged as this could have been potentially catastrophic for the whole country. Engineering work will need to be part of the wider relief effort to ensure the rapid restoration of essential services in the region.”