Wenchuan, China (2008 Earthquake)

Introduction

On May 12, 2008, at 14:28:04 (Beijing Time), an Ms 8.0 earthquake struck Wenchuan, a small county of Sichuan Province in southwest China. The quake lasted for about 18 s. The geographic coordinates of the epicenter were N30°57′ and E103°24′; and the focal depth was estimated at 14–19 km. The Wenchuan Earthquake sequences included one major shock (Ms 8.0) and many fairly large aftershocks (Yuan, 2008). Within 3 months after the major shock, over 20 aftershocks exceeded Ms 5.4. The main shock and the aftershock sequences were scattered along the seismic faults, as indicated in Figure 1 (USGS, 2008; China Earthquake Administration Monitoring and Prediction Division, 2009).

Wenchuan, China (2008 Earthquake), Figure 1

Distribution of main shock and aftershocks of the Wenchuan Earthquake, M - moment magnitude, preferably being used for M8+ shocks (After USGS, 2008; China Earthquake Administration Monitoring and Prediction Division, 2009).

Geologically, the Ms 8.0 Wenchuan Earthquake occurred on the Longmenshan faulting belt, a large, active, partly strike-slipping, partly thrust-faulting belt in the middle of the north-to-south seismogenic zone and on the eastern edge of the Qinghai-Tibet Plateau in China. The instrumental epicenter was in the middle of the Longmenshan faulting belt, below Yinxiu Township at the west of Dujiangyan and the south of Wenchuan County (Figure 1). The northeast trending Longmenshan faulting belt belongs to a fault system that was formed by the Mesozoic orogenesis. It is 500 km long and 40–50 km wide. The fault belt starts at Luding and Tianquan, at its southwest end, passes through Baoxing, Guanxian, Jiangyou, and Guangyuan, all in Sichuan Provinces, and finally enters into Ningqiang and Mianxian in Shaanxi Province at its northeast end.

The Ms 8.0 Wenchuan Earthquake created two new surface fractures inside the Longmenshan faulting belt, that is, the Wenchuan Earthquake fractures. The major surface fracture is over 250 km in total length, extending parallel to the middle and northern sections of the Longmenshan faulting belt. The secondary surface fracture extends along the Guanxian-Jiangyou fault of the Longmenshan faulting belt, with a discontinuous length of 90 km.

The Wenchuan Earthquake was shallow-focused, and thus caused significant damage and loss. The relative location of the earthquake epicenter inside China is shown in Figure 2. This earthquake affected almost all the population within a radius of 200 km around the surface epicenter. Except Heilongjiang, Jilin, and Xinjiang, all provinces in mainland China were shocked by this terrible earthquake, with Sichuan, Shaanxi and Gansu suffering the most. The shock was also felt in several countries in eastern Asia, including Thailand, Vietnam, Philippines, and Japan. Based on the Chinese Seismic Intensity Scale (CSIS), the intensity of the Wenchuan Earthquake is shown in Figure 3 (China Earthquake Administration Monitoring and Prediction Division, 2009).

Wenchuan, China (2008 Earthquake), Figure 2

Epicenter of the Wenchuan Earthquake in China.

Wenchuan, China (2008 Earthquake), Figure 3

CSIS-based intensity map of the Ms 8.0 Wenchuan Earthquake (China Earthquake Administration Monitoring and Prediction Division, 2009).

According to detailed investigations after the earthquake, the disaster area was classified into four categories of damage: (1) extremely severe, (2) severe, (3) heavily affected, and (4) slightly affected (National Disaster Relief Commission, 2008). The distribution of the four categories and the demographical statistics are shown in Table 1.

Wenchuan, China (2008 Earthquake), Table 1 Demographics of each category of the Wenchuan Earthquake severity (National Disaster Relief Commission, 2008)

Casualties

As of May 5, 2009, 69,220 people died, 374,643 people were injured, and 17,923 people were missing as a result of the Wenchuan Earthquake. The casualty statistics of each province are shown in Table 2 (National Disaster Relief Commission, 2008). Table 3 indicates the extent to which the extremely severe areas suffered in the categories of casualties and building collapses (National Disaster Relief Commission, 2008).

Wenchuan, China (2008 Earthquake), Table 2 Casualty statistics by provinces (National Disaster Relief Commission, 2008)

Wenchuan, China (2008 Earthquake), Table 3 Casualties and building collapses in the category of “extremely severe” (National Disaster Relief Commission, 2008)

Economic losses

The Wenchuan Earthquake caused a direct economic loss of 845.14 billion RMB, approximately US$122.85 billion (2008 dollars) (National Disaster Relief Commission, 2008). Among all the losses, Sichuan Province suffered the most, accounting for 91.3% of the total losses; Gansu Province accounted for 5.8%; and Shaanxi Province accounted for 2.9%. The combined losses of other provinces were about two billion RMB (US$0.29 billion ).

Among all the losses, buildings and infrastructures accounted for the most, up to almost 70% of the total losses. Ranked by the percentage share of the total losses, losses of civil buildings were ranked the first, at 24.7% of the total losses; infrastructure, including roads, bridges, and other municipal facilities, ranked second at 21.9%. Nonresidential buildings, including schools, hospitals, and other public buildings held third at 20.4% of the total losses.

The direct economic losses of the disaster areas comprised 2.81% of China’s GDP in 2007. The losses of Sichuan Province alone accounted for 58.80% of the provincial GDP in 2007, and 2.51% of China’s total GDP.

Earthquake prediction and preparation

Seismic zoning and earthquake preparation

China’s Code for Earthquake Resistant Design of Buildings and the Seismic Zoning Map (State Seismological Bureau, 1992) have been put into force to set standards for the buildings and infrastructures all over the country, but adherence to these codes and regulations were not compulsory in less-developed areas until 2006 because of economic factors. Before this earthquake, these codes and regulations set the maximum seismic intensity at CSIS VI for all the extremely severe disaster areas and at CSIS VII for a few of the more potentially severe disaster areas (Shi and Li, 2001), because there had been no large earthquakes in this area before these codes was established. According to these earthquake resistant design codes, infrastructure in areas of CSIS VI and below would be built with no earthquake-resistant design. Earthquake-resistant design was only mandatory in areas of CSIS VII and above. Therefore, seismic resistant capabilities of buildings designed by such standards would not have met the required strength to withstand such a shallow focused Ms 8.0 earthquake.

Earthquake prediction

Whether the Wenchuan Earthquake was predicted or not aroused many controversies and rumors in both international and Chinese societies. Unlike the 1976 Tangshan earthquake in China, the middle section of the Longmenshan faulting belt – the meizoseismal area of the Wenchuan Earthquake – had been considered inactive before this earthquake according to analyses of Chinese mainstream earthquake experts. Compared with the middle section of the Longmenshan faulting belt, the Xianshuihe faulting belt, the Anninghe-Zemuhe-Xiaojiang faulting belt, and the Songpan-Ganzi faulting zone in the southwest China had more tectonic activities, and attracted much more research attention; thus, many seismic monitoring measures and research efforts were applied to those areas. However, prior to the Wenchuan Earthquake, a few Chinese specialists and American experts did give a fairly accurate middle-term prediction for the possible earthquake, and some advice for future research. Unfortunately, such predictions and research findings were not accepted by the mainstream earthquake experts in China. Obviously, earthquake prediction is still not an exact science and remains an unsolved world-class challenge. A large gap still exists between the actual problem-solving ability of scientists and the need for community disaster preparation.

Emergency responses and relief measures

After the occurrence of the Wenchuan Earthquake, the Chinese government immediately began an emergency rescue and relief program (China Earthquake Administration, et al., 2010). Headquarters for victim rescue and disaster relief were established all around the affected areas.

According to statistics issued by the Headquarters at the State Council, all relevant ministries and organizations of the Chinese central government had allocated a large amount of resources and exerted many efforts during the disaster relief campaign. As of May 24, 2008, the Headquarters had mobilized 111,278 soldiers, 22,970 armed policemen, 24,401 special policemen, 4,000 specialized earthquake rescue workers, 88,341 medical workers, and 6,013 volunteers to help in the disaster areas. As of June 14, 2008, the central government and the local governments had allocated 1.31 million tents, 4.82 million quilts, 14.09 million articles of clothing, 1.04 million tons of liquid fuel, and 2.23 million tons of coal to the disaster area. As of August 4, 2008, the central government and the local governments had devoted 64.16 billion RMB to the disaster areas, and about 59.41 billion RMB was received from public and private donations for the disaster relief.

After the occurrence of the Wenchuan Earthquake, the international society expressed its sincere sympathy to the Chinese people through the central government, together with various kinds of support. As of July 18, 2008, the Chinese Ministry of Foreign Affairs and other Chinese embassies and diplomatic missions all over the world had received about 1.71 billion RMB in donations, including 0.77 billion RMB from foreign governments, international, and regional organizations; 1.99 million RMB from foreign embassies, diplomatic missions, and individuals in China; and 0.94 billion RMB from foreign civilian organizations, foreign enterprises and individuals, overseas Chinese, Chinese scholars and students living overseas, overseas branches of China-based companies and organizations, and other individuals.

Recovery and reconstruction after the earthquake

One month after the Wenchuan Earthquake, the Chinese central government began to implement recovery and reconstruction work by establishing basic guidelines (Wen, 2008). At the same time, the relevant ministries jointly issued specific instructions to direct the recovery and reconstruction work. In September 2008, the State Overall Planning for Post-Wenchuan Earthquake Restoration and Reconstruction (SOP) was issued (State Planning Group, 2008).

According to the statistics issued by the China Ministry of Finance, by May 4, 2009, the Chinese central government had supplied almost 85 billion RMB to the disaster area for the recovery and reconstruction. By the end of 2009, 160 billion RMB from the central government and 17 billion RMB from the provincial government were allocated to the affected areas in Sichuan province. In addition, a total of 250 billion RMB was available from other provincial governments through the “Twin Assistance” program, social donations, contributions from Hong Kong, Macao, and Taiwan, and rehabilitation funds from the county and city governments of the affected areas.

Following the SOP, 29,704 recovery and reconstruction projects were planned for Sichuan Province, the worst-struck province, including 1,500,000 rural dwelling houses, 259,000 urban dwelling houses, 3,002 schools, 1,362 medical and health institutes (including hospitals), and 38 towns and cities.

As of March 2010, 95% of these projects were being implemented, and 74% were completed; special efforts were made to care for the most vulnerable groups (China Earthquake Administration, et al., 2010).

Parallel to the Chinese central government’s efforts, recovery projects assisted by international loans were also being implemented. The World Bank loaned a total of US$710 million to the Chinese central government for recovery and reconstruction projects in Sichuan and Gansu Provinces for a period of 5 years from March 2009 to March 2014 (World Bank, 2009). As of June 2010, US$116 million had been disbursed for infrastructure, health, and educational projects (World Bank, 2010). One year later, the cumulative disbursement reached 35% of the total loan, and the progress on the project was moderately satisfactory (World Bank, 2011).

In March 2012, the Chinese central government announced that the SOP recovery and reconstruction tasks were completed; the basic working and living conditions and the level of economic and social development in the disaster areas were significantly better than that before the earthquake (NDRC, 2012).

Cross-references

Casualties Following Natural Hazards

Earthquake

Earthquake Damage

Earthquake Prediction and Forecasting

Earthquake Resistant Design

Tangshan, China (1976 Earthquake)