The trouble with tsunami warnings

The Fukushima disaster has unfortunately overshadowed the real problems that Japan has. Namely half a million people having lost their homes, who will never come back – both because their homes are destroyed and local authorities forbidding the rebuilding of homes in areas hit by the tsunami – and twenty thousand having lost their lives

Especially the latter problem could have been prevented by building sufficiently high seawalls, as in the village/town of Fudai. although only or not settling on the coastal plain after the devastating 1896 and 1933 tsunamis.

It would have also helped if people had not gone berserk with tsunami warnings after the 2004 tsunami. Scores if not hundreds of tsunami warnings have been issued since then. Virtually all of them were false positives. Only three actually happened in 2006, 2007 and 2009.

After countless false tsunami warnings had been issued because of the aftershocks of the 2004 earthquake, upsetting the population to the point that they were throwing stones at the sirens (how would you feel uselessly running for your life once a month or so?), Indonesian authorities did not issue a tsunami warning in the 2006 earthquake that caused another tsunami. The Solomon Island earthquake of 2007 generated a damaging tsunami that arrived before an alert had been issued. Once it had done damage, however, a tsunami warning was issued for all of the south pacific – were it didn’t do any damage at all. The 2009 tsunami in Samoa was a similar story.

In all cases, the warnings extended far beyond actual damages. Most warnings had no associated tsunami anywhere (20cm or 50cm is not a tsunami). The best policy in case of a tsunami warning today is to ignore it. It’s wrong anyway. Even if the tsunami did damage, it has an incredibly high chance not to damage your area – because you’ve heard the warning and damage is usually done before the warning is issued. (Except for really large tsunamis as in Japan 2011 or Indonesia 2004.)

If tsunami warnings could be relied upon to be relevant even in as little as 33% of the cases (instead of less than 1%), it would suddenly start to make sense to behave properly and do what you ought to do when a tsunami is headed for you: run for your life – which tens of thousands failed to do in Japan.

No wonder. Just 2 days before, when a mag 7.3 precursor event happened, the tsunami that people were warned to expect had failed to materialize.

I remember that one, because on March 9th or 10th I looked up the earthquakes in Japan and was surprised to find out, that just one earthquake in the last decades was comparable to this one – the Kobe earthquake. I thought Japan had had much worse earthquakes of about mag 8 or so. But they hadn’t. Well, one or two days later, I remember waking up, switching on the radio and hearing about a mag 8.9 earthquake in Japan …

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