HK tsunami risk is small, but one we can't ignore

PUBLISHED : Sunday, 24 April, 2011, 12:00am
UPDATED : Sunday, 24 April, 2011, 12:00am


Few major cities can match the safety standards Hong Kong has attained. We've got a low crime rate, terrorism has so far been mercifully absent, and we would seem to have all but tamed our natural environment. Typhoons that once left heavy death tolls are now easily weathered, while high building standards protect our homes and offices from the earthquakes that have in the past caused tragedies. Experience, preparedness and preventative measures have given us this security.

Being safe isn't reason for complacency, of course. Nature has been brutal to our city, with thousands killed by natural disasters in the past century. The worst was a nine-metre tidal wave whipped up during a typhoon that in 1937 took 15,000 lives. To describe it as an unprecedented freak of nature would probably be wrong - disasters in south China in past centuries were not as accurately recorded as those in recent times.

It's for this reason that we should not dismiss a researcher's computer simulation showing the dangers to Hong Kong of a quake measuring 9.0 on the Richter scale beneath the South China Sea. Were it to occur in what is known as the Manila Trench, a tsunami of between five and eight metres would smash into Taiwan in 15 minutes and breach our shores about an hour and 45 minutes later with catastrophic results, University of Minnesota professor David Yuen and his team concluded. There's a chance of it happening within 50 to 100 years. Yuen is not trying to be alarmist; he's merely mapping seismic probabilities in a part of the world for which little research into quakes and tsunami has been done.

Such work is about determining risk, and it would be foolish to pretend it doesn't exist. The 1937 disaster amply proves that. But even more so are records of a quake and tsunami in the South China Sea in 1782 that is believed to have killed 40,000 people, the most victims of such a disaster until that which struck the Indian Ocean in 2004. Four tsunami have affected our city in the past half century, although none caused a tidal surge of more than half a metre.

The quake and tsunami in Japan last month and the resulting nuclear reactor crisis have prompted the question: could it happen to us? We've got the Daya Bay power plant just 50 kilometres away, one-fifth the distance of the crippled Fukushima Daiichi station from Tokyo. Japan straddles a quake zone and has always battled tsunami - the word is Japanese. Yet, for all its experience, technological prowess and preparedness, as many as 28,000 people could have been killed and the possibility of a nuclear calamity remains.

All manner of assurances have been given by Daya Bay's operators. The complex has been built to withstand a quake of 8.0, and one that powerful hasn't been recorded in what is determined to be a seismically stable area; the strongest in 1911 measured 6.0. On land seven metres above sea level and protected by a 17-metre breakwater, the biggest tsunami on the stretch of coast was 50 centimetres. They would seem markedly different circumstances from the Fukushima plant, also seven metres above sea level, in an active seismic zone, which was swamped by a 13-metre wall of water after the worst tremor and tsunami Japan has recorded.

Speculative research isn't cause for fear and worry; rather, it's a reason for more in-depth study. We have to determine whether there is a real danger and if from our best methods find that there is, make plans as to what to do about it. Such assessment and response is how we can most reliably keep Hong Kong as safe as possible.