Comparison earthquakes of Yushu and Ning'er in Qinghai and Yunnan of China

Yushu earthquake of magnitude 7.1 in Qinghai on April 14, 2010 and Ning'er earthquake of magnitude 6.4 in Yunnan on June 3, 2007, both are moderately strong earthquakes near the town at the epicenter.

Similarities between the two earthquakes:

Time: Both earthquakes occurred in the small hours of the morning, and most residents were sleeping.

Place:The epicenter of both earthquakes were near the county town. The epicenter of Ning'er earthquake was only 2km away from the county town. Although the epicenter of Yushu earthquake was 39 km away from Jiegu town, but the causative fault of Yushu earthquake extended to the vicinity of the county town.

Area:The areas where the earthquake occurred were all ethnic minority areas. Ning'er County was Hani and Yi Autonomous County, while Yushu was a Tibetan Autonomous Prefecture.

Earthquake damage:Both earthquakes caused serious damage to county town buildings and urban infrastructures, all the phenomena of water supply, power supply and communication interruption occurred.

Differences between the two earthquakes:

Casualties:Casualties caused by the two earthquakes were quite different. Up to April 25 2010, 5:00pm, 2220 people died, 70 were missing and more than 12135 were injured in the Yushu earthquake. 3 people died and 313 were injured in the Ning'er earthquake. The magnitude of Yushu earthquake was 7.1, and Ning'er was 6.4, with a difference of 0.7, the seismic wave energy released by Yushu earthquake was about 13 times than Ning'er.

The dwellings structure of Yushu are mostly composed of adobe structure and hollow brick structure, and Ning'er is wooden frame tile-roofed house structure mostly. Comparing with the two earthquakes in Ning'er and Yushu, besides the magnitude of earthquake destructive force, there are also differences in earthquake prevention and disaster mitigation consciousness, architectural structure form and traditional habits of the residents in the two places. Analysis and study of these differences have reference significance to other counties for how to carry out earthquake prevention and disaster reduction work.

Residential buildings and structure forms

Yushu County is located in the eastern part of the Qinghai-Tibet Plateau, with an average altitude of 4493.4m and cold climate, which is a Tibetan Autonomous County with animal husbandry as master, combining agriculture with animal husbandry, the Tibetan population accounts for over 96% of the total population of the county. Most of the houses in Yushu rural areas are adobe and hollow brick structures, the roof is generally heavier, which belongs to the worst type of aseismic performance in China. According to the preliminary investigation by the on-site emergency team of the Seismological Bureau of China, almost all of these structure houses collapsed or seriously damaged in Jiegu Town, an extreme disaster area.

Ning'er County is the hometown of Pu'er Tea, the starting point of the ancient tea-horse road, rich in forest resources, high vegetation coverage, hotter climate. The houses of Ning'er Hani nationality are generally 2-storey wooden frame tile-roofed house structure with brick walls or adobe outer walls. Compared with the dwellings in Yushu, the houses of wooden frame structure in Ning'er area have good aseismic performance. When Ning'er Earthquake occurred in 2007, the main structure wooden frame of this kind of house basically keeps standing, main earthquake damage were roof tiles sliding and adobe wall collapse. Due to the protective function of the wooden frame, adobe walls had collapsed to outside the house, avoiding the inward collapse and hurting people. Roof tiles fell mainly on the second floor, whereas local residents were used to sleep downstairs (the first floor was cool), and the second floor was only a pile of debris, which were the objective reasons for less casualties in Ning'er earthquake.

Disaster prevention awareness and earthquake drill

Ning'er County belongs to the area where earthquakes are relatively active，on average, an earthquake of magnitude 5 to 6 or so will occur every 10 years. Frequent seismic activities have greatly enhanced the awareness of earthquake prevention for local residents. Six months before the magnitude of 6.4 Ning'er earthquake, local earthquake drills were held, especially in primary and secondary schools. For example, the Tongxin Township Middle School of Ning'er County, after the earthquake, students living in school withdrew to school playground orderly according to the drill plan without the guidance of teachers. None of the students was injured by the earthquake, and no more crowding caused by panic of the earthquake.

In contrast, the awareness of earthquake prevention and disaster reduction in Yushu residents was relatively weak, especially in rural areas. Local housing structure rarely adopted aseismic measures. Take the hollow brick structure as an example，this building should be used as temporary housing only. If as a housing, which need to add core columns and other aseismic measures. Unfortunately, most local residents didn't take notice when they built their houses. It was relieved that the lessons learned from Wenchuan earthquake played an important role in this earthquake. Take the Nationality No.1 Middle School of Yushu as an example, the first earthquake of magnitude 4.7 occurred at 5:39 am on April 14, the leaders and teachers on duty at school felt that the situation was not right，they organized students to evacuate to the playground and eluded the main earthquake 2 hours later successfully. It was inseparable that the school usually payed attention to the safety education, often organized students to conduct earthquake drills.

Comparison of earthquakes in Yushu and Ning’er, we can find that the strong and weak consciousness of earthquake disaster prevention and mitigation has a decisive influence on the degree of earthquake damage. The stronger awareness of earthquake prevention and disaster mitigation, the stronger ability to resist earthquake disasters, disaster losses may be less, otherwise earthquake disasters will inevitably aggravate. The persistent awareness of disaster prevention is a prerequisite for earthquake disasters mitigation.

(Excerpts from Aiwen Liu《Comparison earthquakes of Yushu and Ning'er, a brief discussion on the disaster reduction measures of the medium and strong earthquakes in nearby towns》)