4. Prediction or providence? – Haicheng 7.3 Ms and Tangshen 7.8 Ms
During the mid 1970’s two earthquakes in northeast China highlighted the immense difficulties involved in predicting earthquakes and their associated impacts. From late 1974 to early 1975 the inhabitants of the province of Liaoning close to the city of Haicheng, witnessed various geophysical and geochemical phenomena that suggested a major earthquake could soon occur. Two official middle-term predictions were published for a large earthquake to take place within close proximity to this area (Wang et al., 2006). Following a number of false alarms it was the occurrence of a series of strong foreshocks that ultimately led the authorities to evacuate the city’s population believing that a strong earthquake was imminent. Almost immediately after evacuation in early February 1975, a magnitude 7.3 event heavily damaged the city. At the time this was considered to be the first successful scientific prediction of an earthquake in China. Evacuation significantly reduced the expected number of casualties, and it was thought that the recognition of precursory signs before its occurrence could be used to predict future earthquakes and save more lives. Eighteen months later at Tangshan (Hebei Province), however, the absence of major foreshocks failed to prepare the authorities for an early morning 7.8 magnitude event and subsequent 7.1 aftershock. The consequences were devastating (figure 5), with over 240,000 lives lost and 93 percent of residential buildings and 80 percent of water pumping stations destroyed. The failure of seismologists to predict this earthquake meant that there was still much to learn, and many questions to answer. Today, Tangshan has been completely rebuilt and is known as the “Brave City of China.”

Figure 5. Heavy damage in Tangshan city within the seismic intensity XI zone (after Chen et al., 1988)

The apparent success of Haicheng and the losses of Tangshan in the 1970’s created a watershed worldwide in relation to earthquake impact and earthquake loss mitigation strategies. As a consequence, while many scientists in China remain fascinated by the search for reliable earthquake prediction, the country also follows a broad and robust approach to earthquake preparedness at many levels in society. Colourful, attractive and informative booklets advise local populations what to do in the event of an earthquake (e.g. What should we do when an earthquake comes? SSB, 1997) so, for example, at the onset of strong ground shaking they are advised to shelter under something strong that will help to protect them from building collapse (figure 6a). The thrust is clearly now towards earthquake preparedness (figure 6b) which requires extensive scientific and engineering investigation in order to maximize understanding of the seismic hazard, building vulnerability and earthquake risk and potential losses.

a)

b)

Figure 6. Pragmatic advice. (a) Act quickly to take shelter during the strong shaking caused by an earthquake and (b) prepare in advance (from SSB, 1997).

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