Nat Hazards (2014) 70:941–949 DOI 10.1007/s11069-013-0817-5 SHORT COMMUNICATION
Ya’an earthquake of 20 April 2013: introduction and reflections Q. X. Meng • W. Y. XU
Received: 16 July 2013 / Accepted: 26 July 2013 / Published online: 9 August 2013 Ó Springer Science+Business Media Dordrecht 2013
1 An introduction of Ya’an earthquake The China Earthquake Networks Center (CENC) recorded that at 8.02 am on 20 April 2013, a 7.0-magnitude earthquake occurred in Lushan County of Ya’an in Sichuan province. The epicentre of the earthquake was located in Miaopingshang, in the town of Shuangshi. The epicentre was 13 km deep and was about 115 km west of the provincial capital, Chengdu. It was also 85 km from the epicentre of the 2008 Wenchuan earthquake. The epicentral intensity was IX, which is the same as that of the Wenchuan earthquake. Over 800 km were affected by the Ya’an earthquake, which was strongly felt over Sichuan province and surrounding areas such as Chongqing, Gansu, Guizhou and Yunan. Figure 1 illustrates the location of the Ya’an earthquake. Ya’an is a prefecture-level city in the western part of the Sichuan province, and it has a population of 1.53 million and an area of 15,300 square kilometres. Popularly known for its tea culture and for being the hometown of the giant panda, and Ya’an is a city with strong traditions and beautiful scenery (Fig. 2). Bifengxia Base is a national reserve as well as the location of a breeding facility that is home to 62 giant pandas, most of which were relocated from Wolong National Nature Reserve following the 2008 Wenchuan earthquake. There were a large number of aftershocks from the Ya’an earthquake. Figure 3 shows the magnitude-time plot and the daily frequency of the aftershocks in Ya’an from 20 April to 23 May 2013, recorded by permanent and portable seismic stations. Up until May 23, more than 132 aftershocks over a magnitude of 3 were measured. There were 4 aftershocks with a magnitude between 5 and 5.9, and 23 aftershocks with a magnitude between 4 and 4.9. Although the daily frequency of the aftershocks decayed quickly, large aftershocks with a magnitude greater than 4 still occurred 10 days after the main shock. Q. X. Meng (&) W. Y. XU Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Research Institute of Geotechnical Engineering, Hohai University, Nanjing 210098, China e-mail:
[email protected] W. Y. XU e-mail:
[email protected]
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Fig. 1 Geographical map of the Ya’an earthquake; the left side is the map of China, and the right side is the location of earthquake epicentre on Google earth
Fig. 2 A glimpse of Ya’an; the left side is the map of Yaan, and the right side is the beautiful idyllic scenery of Lushan County shot on 20 March 2013 (Source Tecent)
2 Geological features Earthquakes are closely linked to local geological characteristics. China sits on the junction of two tectonic plates and is one of the world’s major earthquake zones. Most of the large earthquakes that have happened in China in the last 100 years have occurred in the southwest of China. In this area, the Sichuan plain meets the Tibetan mountains and forms a large crack in the earth’s crust, called the Longmen Shan Fault (Fig. 4). However, the eastern Tibetan Plateau is not the main reason for these earthquakes, and its formation and development is largely due to the collision of the Indian and Eurasian tectonic plates. The
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Fig. 3 The aftershocks series of Ya’an earthquake (Source www.csi.ac.cn)
Fig. 4 The geological features of Longmen Shan Fault (MIT Report 2008)
Longmen Shan Fault runs southwest to northeast, between 30° and 34° north and 103° to 106° east, over a length of 500 km and a width of 70 km. Motion on this fault is responsible for the uplift of the mountains relative to the lowlands of the Sichuan Basin to the east. The persistent bearing stress on the crust, caused by the eastern Tibetan Plateau, builds until a fracture forms in the stuck rocks of the crust. The plates then jump past each other, releasing energy in the form of earthquakes. This causes this area to experience frequent seismic shocks. Huang (2009) detailed the historical earthquakes that have occurred in this area, as shown in Fig. 5. The frequency of seismic activity in this area has been so high that more than 13 earthquakes with a magnitude of 6 or larger have occurred in the area during the last 400 years. After the magnitude 8 Wenchuan earthquake struck in 2008, based on an interview from Guangming Daily (available at: gmw.cn), an expert believed that the stress between the plates had been released and there would be no violent shocks in a 100 years. On the contrary, a paper published in Nature showed that the stress was released mainly in the central and northern Longmen Shan Fault, while in the southern part (where Ya’an is
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Fig. 5 The historical earthquakes occurred in Longmen Shan Fault zone
located) the stress was predicted to rise and suggested large aftershocks in the near future (Parsons et al. 2008).
3 Earthquake damage 3.1 Casualties Although the Ya’an earthquake is not expected to be as disastrous as the 8.0-magnitude Wenchuan earthquake that occurred in the same province 5 years ago and left 87,000 dead or missing, it has still resulted in serious casualties and economic losses. The Ya’an earthquake happened at 8 am, when people were out of bed and able to react but before children had gone to school. In Wenchuan in 2008, many of the casualties were caused by collapsing school buildings that crushed students who were already in their classrooms. This may be the single most important factor for the reduction of injuries and
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deaths in the Ya’an earthquake. The relationship between the distribution of earthquake intensity and population density is shown in Fig. 6, which is based on the information acquired from Baidu Position and CENC. Because there is only one populated area near the epicentre, there was a lower risk of casualties, and Ya’an was able to avoid a large death toll. According to the People’s Daily (available at people.com.cn), as of April 26, 196 people had died, 13,484 were injured, 21 were still missing and more than 2 million suffered from the results of the 7.0-magnitude earthquake. More than 176 people died in Ya’an, which was the worst affected disaster area (Table 1). 3.2 Damage to buildings and surroundings During the Ya’an earthquake, strong ground shaking and low earthquake resistance led to severe damage to the buildings (Fig. 7). Although the national survey data have not yet been collated, the website of Sichuan Provincial Department of Civil Affairs (21 April
Fig. 6 The distribution of earthquake intensity and population density of Ya’an Earthquake (Source Baidu)
Table 1 Death toll in different districts of Ya’an City
District
Death toll
Lushan
120
Baoxing
29
Mingshan
2
Tianquan
5
Yucheng
15
Yingjing
2
Hanyuan
1
Shimian
2
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2013) reports that about 718,000 housing units were damaged in the earthquake, as many as 56,000 housing units collapsed, and 45,000 housing units were seriously damaged. More than 250,000 housing units were affected in the two heavy disaster areas of Lushan and Baoxing. The Ya’an earthquake also caused great destruction to transportation facilities (Fig. 8). Ya’an is located in a mountainous area where most transportation occurs by road, followed by water carriage. The roads in the Ya’an area can be categorised into three types: national, county and rural. The People’s Daily (July 3) reported that the Ya’an earthquake damaged 432 km of national roads, 3,689 km of county and rural roads, 86 bus stations and 59 docks.
Fig. 7 The damage to the buildings in Ya’an earthquake: the left side is the aerial photography of damaged and ruined house in Taiping Town, Lushan County, and the right side is a collapsed house of Qingren Town, Lushan County (Source Tencent, Sina)
Fig. 8 The damaged roads during the Ya’an earthquake (Source chinahighway.com)
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Fig. 9 The scared panda that refused to come down (Source Xinhua)
The Ya’an earthquake also affected the region’s infrastructure. A total of 24 electricity substations and 224 power lines were damaged, and the Lushan, Tianquan and Baoxing power grids were completely paralysed. A total of 724 fixed and mobile communication base stations were damaged, leading to a loss in telephone communication for 16 townships. In addition, the Ya’an earthquake damaged 34 reservoirs, which were categorised as secondary hazards. Luckily, following the Ya’an earthquake, all of the giant pandas in the Bifengxia Base breeding facility were confirmed to be safe. However, some of the young pandas were so scared that they climbed up the trees and refused to come down (Fig. 9).
4 Emergency response and rescue The response of the emergency services following the Ya’an earthquake showed that lessons had been learned from the 2008 Wenchuan earthquake. In addition, the Chinese government showed its human spirit and virtues, both to the nation and to the world. Disaster emergency response at the central and local levels started shortly after the earthquake occurred. Chinese President Xi Jinping and Premier Li Keqiang ordered all possible measures to be taken to rescue the victims and to minimise the deaths and injuries. The joint action from different departments of the Chinese government showed that the government response was very efficient. For example, the electricity supply and communication links recovered just 12 h after the initial shock. Thousands of members of the Liberation Army, armed police, the fire brigade, as well as militia and reserve forces quickly arrived at the affected areas to immediately carry out rescue work. However, unfortunately, People’s Daily (available at: people.com.cn) reported two young soldiers were killed on the way to disaster area due to the traffic accidents on April 20 and 21. During the Ya’an earthquake, the media reported full, timely, transparent and comprehensive information. Less than 10 min after the earthquake, the China Earthquake Administration (CEA) collaborated with the Xinhua News Agency to release news about the earthquake to the community. Major Web sites set up special topics on the disaster and provided up-to-date information on the relief operations. In addition, as in the reaction in Wenchuan earthquake, the disaster relief received numerous monetary donations and other forms of aid from the volunteers, NGOs and other
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countries and regions. One highlight of this is that the NGOs stood out and asserted their influence.
5 Reflections 5.1 The implementation of building standards The quality of construction played a significant role in the Ya’an earthquake. The damage caused to different kinds of houses is listed in Table 2, which is based on the damage statistics for various structural types during the 2008 Wenchuan earthquake (Chen and Booth 2012). The suburbs of Ya’an mainly contain houses built by the occupiers, which are usually brick or mixed structures, and accounted for a large part of all of the damaged or collapsed buildings during the Ya’an earthquake. Because most of these houses are built by residents, the quality differs based on their experience and on the traditional building techniques used. Furthermore, the shortage of money has made, and it is impossible for these builders to use better materials, such as cement and steel. Although the local government gives a subsidy to encourage local farmers to build houses that adhere to modern building standards, this policy has not worked because many people in the local area are poor, and the subsidy is not large enough to make up for the high cost of observing modern building standards. The historical frequency of earthquakes along the Longmen Shan Fault in western Sichuan makes it very likely that there will be more earthquakes in this area. Therefore, it is important that local authorities make it easier or less costly to upgrade building standards so that the number of deaths and injuries that are caused by these factors is significantly reduced. 5.2 The rise of social media The response to the Ya’an earthquake demonstrates that social media is a new and increasingly important feature of earthquake disaster response. For example, social media played a significant role in the spread of information and disaster relief following the Ya’an earthquake. The earthquake struck at 8.02 am. At 08.29 am, the China International Rescue Team posted a message on Weibo (a Chinese microblogging website) that gave details of the earthquake and asked for those affected to report what they saw and whether they had been hurt. The message was forwarded more than 400,000 times, and it received more than 37,000 responses. Other applications of Weibo (such as microblogging tracing) were highly efficient during the disaster relief operations. Table 2 Damage statistics for various structural types Minor damage: can be used
Moderate damage: repair required for further use
Serious damage: further use prohibited
Demolition essential
Brick structure
42 (21 %)
74 (37 %)
33 (16 %)
52 (26 %)
Mixed
20 (48 %)
9 (21 %)
4 (10 %)
9 (21 %)
Steel-reinforced concrete frame
66 (63 %)
40 (38 %)
8 (8 %)
9 (9 %)
366 buildings were investigated
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China’s social media was not yet a significant force when the Wenchuan earthquake struck in 2008. However, the response of the social media to the Ya’an earthquake shows that it has now become a powerful tool that is able to keep the public informed and allows them to express their opinions. Consequently, we predict that future disaster relief efforts will be more transparent thanks to the influence of social media. 5.3 Rational volunteer The growth of social media may have helped the Ya’an earthquake to draw a lot of public compassion. For example, volunteers from all walks of life tried to show their support for the victims of this disaster. However, in reality, these actions were not only unprofitable but also many were also harmful. According to the local government, untrained and unprepared volunteers flocked to the earthquake-stricken Longmen Town in Lushan County, causing unnecessary transport jams and consuming significant quantities of desperately needed disaster relief materials. Many of the volunteers not only lacked professional skills and equipment, but also they did not even have the ability to protect themselves (let alone rescue others). On the contrary, a significant part of the precious resources of the area was occupied to provide for these volunteers. For example, on April 23, the Xinhua News Agency reported that more than twenty volunteers from Xian, Shanxi were stuck on a mountain on their way to the quake area. Hence, it is recommended that only trained volunteers should be used during the rescue operations. Volunteers without specialised training are encouraged not to go immediately into disaster centres and should instead save their efforts for the post-disaster recovery operation. Acknowledgments The authors would like to thank financial supports from the National Key Technology R&D Programme (2013BAB06B00). We also acknowledge the editor for the valuable suggestion.
References Chen Y, Booth DC (2012) The Wenchuan earthquake of 2008: anatomy of a disaster. Springer, Berlin Huang R (2009) Geohazard assessment of the Wenchuan earthquake. Science Press, Beijing MIT Report (2008) Earthquake near Wenchuan, West Sichuan, China 2008 May 12 06:28:01 UTC; Magnitude 7.9. http://quake.mit.edu/*changli/wenchuan.html. Accessed 23 Mar 2011 Parsons T et al (2008) Stress changes from the 2008 Wenchuan earthquake and increased hazard in the Sichuan basin. Nature 454(7203):509–510
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