Why some earthquakes are so deadly

Now the whole house is shaking. What to do?

The answer depends less on the magnitude of the earthquake than you think. What matters most is the country in which you live and your proximity to the water.

Take, for example, the largest earthquake you have ever heard of. This happened on February 27, 2010 off the coast of Chile. It was the sixth largest ever, with a magnitude of 8.8.

This did not go unnoticed. This caused three minutes of intense shaking in Chile and Argentina. The tsunami it generated caused damage as far away as Japan.

However, only 550 people died during the earthquake, including 150 during the tsunami that followed, and the public was quick to listen.

Compare that to what happened in Haiti a month earlier, January 12, 2010. This one you'll remember for sure because it was awful, and you and countless other people donated to the rescue and recovery effort.

Nobody knows for sure how many people died: 160,000? 220,000? But this earthquake was only of a magnitude of 7.0. In the world of logarithmic scaling, this means that Chile was 500 times more powerful. So why was the earthquake in Haiti so devastating?

Blind fault

The classic saying among geologists is that earthquakes do not kill people, buildings have them. Or bridges. Or failing dams. Or the fires of broken gas lines.

Or an epidemic of cholera that stems from the lack of drinking water.

Nothing makes more difference in the number of deaths from an earthquake than the infrastructure, especially when the population is dense. Chile has a long history of earthquakes. The largest ever recorded, with a magnitude of 9.5, struck in 1960. It also has the building codes to show. Haiti did not have the resources to prepare or react adequately.

Another difference is the wait. The earthquake in Haiti has occurred on what is called a blind fault, that is to say, that she was buried. We did not know that it existed.

The fault in Chile appears all the time. And the Pacific countries now know that they can be struck at any time by a tsunami from Chile or any other place.

After the devastating earthquake that struck the Sumatran coast on December 26, 2004, which triggered the post-Christmas tsunami that killed more than 200,000 people, an international effort intensified the deployment of a buoy alert system. in the Indian Ocean.

The unexpected in Sulawesi

So, what happened so bad on September 28, 2018 in Sulawesi, Indonesia? The magnitude 7.5 earthquake was important, but not huge. The real killer and the surprise was the tsunami. So far, about 2,100 deaths have been reported, but their number continues to increase.

Tsunamis are devastating – inevitable and almost unfathomable if you are on their way. They usually occur by changing the shape of the seafloor during the earthquake.

But the Sulawesi earthquake did not occur under water. Instead, the tsunami may have been a side effect: the earthquake triggered an underwater landslide and the landslide triggered the tsunami.

Would an early warning system have helped? Perhaps, but as we did not expect this kind of tsunami, even if a network of buoys had worked, they would not have been in the right place because the tsunami was so local.

They would not have warned the locals either because the tsunami followed so quickly after the earthquake – in this situation, the earthquake itself was the best early warning system.

What should you do?

Do not think we are immune to major or unexpected earthquakes in Canada. Vancouver is ready for the "big". In Quebec and Ontario, there are sometimes rumblings along ancient tectonic scars. Earthquakes along such faults are the most difficult to predict because they occur so rarely.

Learning to accurately predict and prepare for earthquakes is a long game. They are so rarely that it is difficult to see the pattern, and therefore difficult to predict the future.

Promising work on "precursor" earthquakes gives warning minutes of a few days. Unfortunately, the best we can do is decide on the magnitude of earthquake risk in a given region over the next few years. And that seems all but certain.

Scientists are working to expand what we know about past earthquakes beyond recorded human history. It helps. But accurately predicting earthquakes and their impact requires money, time and a lot of extremely detailed work.

So what do you do when you feel the shock of an earthquake? In Chile, dive under cover; your building will probably remain standing. In Haiti, go out in the open. If you are near water, as in Sulawesi, do not wait for the sirens, head to the hills as fast as you can.

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