Sunday, February 28, 2010

Earthquakes and tsunamis

So, yesterday (CET) was the day that the tsunami generated by the recent earthquake of the coast of Chile reached Hawaii, Australia and New Zealand (obviously it reached other nations as well).

Tsunami watch
Unlike pretty much every other major tsunami warning in history, it was possible to follow live camera watches of the Hawaiian coast (I was following it on This was due in part to the developments in technology, but more importantly to the work of the scientists involved (geologist, oceanographers, seismologists, hydrologists etc.) who were able to predict, quite accurately, when the tsunami would hit (the long distance from Chile to Hawaii also gave more time to setup the required infrastructure).

  Timeline of tsunami progress (courtesy of San Francisco Chronicle)
The tsunami was predicted to reach the southern areas of Hawaii at around 11 am local time and incredibly the first reports of water receding rapidly from Hilo bay were coming in shortly after 11 o'clock.
Very impressive work by the scientists and specialists involved.

Timeline of tsunami by country (Courtesy of Washington Post)

Not only did it give a unique opportunity to follow the tsunami, but more importantly it gave the residents of Hawaii (and the other affected nations) time to evacuate and begin preparing for the possible disaster. Very rarely do we have hours to prepare for a natural disaster like this.

Tsumani effect
The tsunami didn't really happen this time (fortunately) and the sea levels in most affected areas only rose 20 cm to around 1½ meter.

But we were all scared that this were going to be a remake of the infamous tsunami after the Indian Ocean tsunami in December 2004 which killed a quarter of a million people.

Why was this important then?
Someone commented on Twitter during the watch that 'it was typical American to turn an earthquake disaster in Chile into a tsunami watch event in Hawaii' (I'm paraphrasing here). That we should have focused on the Chilean disaster instead of worrying about American lives.

At first I just smiled and didn't think anything of it, but today I realized that I completely disagree with that statement. And I hope whoever posted it wasn't serious (I can't remember who it was).

Sure a large scale disaster was happening in Chile, but with the Indian Ocean tsunami still fresh in our memory, we all feared that a lot more lives would be lost. Not thousands (as is usual with major off-shore earthquakes) but tens or hundreds of thousands as we sometimes see when tsunamis strike (the current death toll in Chile is at around 700 lives lost, which is terrible on its own).
We weren't being arrogantly fearing American lives (I'm not even American!) but we were generally fearing for the lives of everyone living in the western coasts of the Pacific Ocean.
The only one being arrogant here was the Tweeter who assumed we didn't care about lost lives.

Earthquakes and tsunamis
So what happened here, surely this earthquake was minor compared to the Haitian earthquake which has killed a quarter of a million people?

Well, not quite. The Chilean quake was measured at a magnitude of 8.8 and the Haitian quake was "only" around 7.0. Which means that the Chilean quake was more than 60 times as powerful as the one in Haiti and released more than 500 times as much energy!

The magnitude scale used (called moment magnitude, it has replaced the previous Richter scale) is logarithmic, where an earthquake one whole number greater has 10 times the amplitude and has approximately 31.6 times more energy.
The logarithmic nature of the scale means that major earthquakes are a LOT more powerful than what appears to be only slightly smaller earthquakes.
In comparison, the Indian Ocean earthquake was measured at around 9.2-9.3 making it 150 times as powerful as the one in Haiti.

What made the Haiti quake so devastating was the fact that it hit on land, directly underneath (around 10-13 kilometres below) an urban area. The Chilean earthquake was 8 km of shore and almost 30 km underground.
The real fear of course, was the possible tsunami. Fearing a remake of the 2004 tsunami or the 1960 tsunami, that also originated in Chile after the most powerful earthquake ever recorded, which caused 10m high waves to hit Hawaii.

Luckily the tsunami didn't happen this time. So now we can focus our attention on the victims in Chile.