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Tuesday 13 May 2008

RAPID ROUNDUP: Experts responds to earthquake in China

Experts comment on the extent of the magnitude 7.9 earthquake in China, including a warning for Australia. Please also see comments from British experts below.

For further technical information on the earthquake and its location, go to the USGS website.

Feel free to use these comments in your stories or contact the AusSMC (ph: 08 8207 7415) if you would like to speak to one of these or another expert.

Kevin McCue is director of the Australian Seismological Centre, Fellow of the Institution of Engineers Australia and adjunct professor at Central Queensland University (CQU).

“My worst fears on hearing of this major very shallow earthquake in SW China have been realised, there is widespread building collapse and loss of life. Many of the collapsed buildings are built with un-reinforced masonry.

The earthquake is an intraplate event, about 500 km from the nearest plate boundary and the mechanism indicates that it was a thrust type event caused by compression across the fault.

The fault rupture in the earthquake was at least 150 km long, a northeast trending arcuate fault clearly visible on satellite photographs. Aftershocks indicate that it initiated at the southwest end of the fault and propagated towards the northeast.

The Chinese earthquake code zones the area as intensity 7 but it is unlikely that the code was followed during construction, and in many places the ground shaking far exceeded the design intensity.

Research over coming months may well show that crustal stress in the epicentral region in SW China was increased following the Sumatran earthquake, the epicentral region is closer to the end of the Sumatran fault rupture than the length of that rupture.

Lessons for Australia are stark:

This was a shallow intraplate thrust-type earthquake like most of the large earthquakes in Australia (Meckering WA 1968, Tennant Ck NT 1988). Australian seismologists believe that a maximum likely earthquake in Australia would have a magnitude of 7.5, the original estimate of the magnitude of this SW China earthquake.

Continental Australia is about 500 km from the nearest plate boundary through Indonesia which is more than capable of producing a great earthquake.

Like China, very few buildings in Australia have been designed or built to resist strong ground shaking and most low rise buildings use un-reinforced masonry in both countries.”

Hong Hao is Professor of Structural Dynamics in the School of Civil and Resource Engineering at the University of Western Australia. Some of the information provided by Professor Hao comes from a Chinese news website

“This was a massive earthquake that was felt by more than half of China, including Beijing, Shanghai, Kunming and Xian. By comparison, the 1976 Tangsha earthquake in China (the most destructive one in the last century, killed about 240,000 people) was 7.6. The 1989 California earthquake (Loma Prieta) was 6.9, the 1995 Kobe earthquake in Japan was 7.2, the 1999 Turkey earthquake was 7.4, and 1999 Taiwan earthquake was 7.6. The 1989 Newcaslte earthquake in Australia was 5.6. The energy released in this earthquake is more than 100 times the one in Newcastle.

The epicentre is Wenchun county, 159 km Northwest of Chengdu. So far most reported building collapses are in DuJiangyan with some damage also reported in Xian. Four primary schools and one high school have collapsed in Deyang county collapsed. Chengdu, Chongqing and Xian airports are closed down. Chengdu and Chongqing railway station are also closed down.

By 22.38 pm (AEST, Monday 12 May) the estimated death toll in Beichun county in China has reached between 3000 and 5000, and the number of injuries has reached 10,000. This is in one county only. By 19:20 pm, 164 aftershocks had been recorded.”

Comments from UK experts (thanks to our colleagues at the Science Media Centre in London):

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 inAugust 25, 1933, killed more than 9,300 people. "

Professor Bill McGuire, from the Benfield UCL Hazard Research Centre, 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 peopleare 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."