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The reason some earthquakes are so devastating

The Toronto Star by Lindsay Schoenbohm 3 October 2018

You feel a jolt. Was that … no, it couldn’t be. But now the whole house is shaking. It must be an earthquake. What do you do? The answer depends less on the magnitude of the earthquake than you’d think. What matters more is what country you live in and how close you are to water.

Take, for example, the biggest earthquake you’ve never heard of. It happened on Feb. 27, 2010, off the coast of Chile. It was the 6th largest ever recorded with a magnitude of 8.8.

It didn’t exactly go unnoticed. It caused eight minutes of intense shaking in Chile and Argentina. The tsunami it generated caused damage as far away as San Diego and Japan. Yet only 550 people died in this earthquake, and it hasn’t lingered in the public awareness.

Compare it to what happened in Haiti just a month earlier, on Jan. 12, 2010. That one you definitely remember because it was awful, and you and millions of other Canadians donated to the rescue and recovery effort. No one knows how many died: 160,000, 220,000? But this earthquake was only a magnitude 7.0, which in the world of logarithmic scaling means the one in Chile was 500 times larger. So why was the Haiti earthquake so devastating?

The classic saying is that earthquakes don’t kill people — buildings do. Or bridges. Or failing dams. Or fires from ruptured gas lines. Or a cholera outbreak that follows from the lack of clean drinking water.

Nothing makes a bigger difference in earthquake death toll than the infrastructure, especially when population is dense. Chile has a long history of earthquakes (the largest ever recorded, a magnitude 9.5, struck in 1960), and has the building codes to show for it. Haiti didn’t have the resources to adequately prepare or respond.

The other difference was expectation. The earthquake in Haiti happened on what we call a blind fault, meaning it was buried below the city, and we literally didn’t know it existed. The fault in Chile pops all the time, and countries throughout the Pacific are now well aware, after the devastating 2004 Boxing Day Indian Ocean tsunami, that they can be hit anytime and have installed a warning system of buoys.

So, what went so wrong in Sulawesi, Indonesia, where the official death toll is 1,350 and climbing? The region was hit by a magnitude 7.5 earthquake on Friday. Big enough, but not giant, and we at least knew about the fault. The real killer, and the surprise, was the tsunami. Tsunamis are devastating — inescapable and nearly unsurvivable if you’re in their path.

Tsunamis happen when you move water in some way, usually by changing the shape of the ocean floor during the earthquake, but the Sulawesi earthquake didn’t happen under water. Instead, the tsunami may have been a secondary effect — the earthquake triggered an underwater landslide, and the landslide triggered the tsunami.

Would an early warning system have helped? Possibly, but because we weren’t expecting this kind of tsunami, even if a network of buoys had been functional, they wouldn’t have been in the right place or given locals enough warning.

Don’t think we’re immune to large or unexpected earthquakes in Canada. Vancouver is poised for “the big one.” There are occasional rumblings in Quebec and Ontario along ancient tectonic scars — earthquakes along faults like this are the hardest to predict because they occur so rarely.

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

There is promising work on “precursor” earthquakes that give days to minutes of warning. Unfortunately most of the time the best we can do is make pronouncements about the chance of a certain earthquake of a certain size occurring in a certain area in the next certain number of years, which sounds anything but certain.

Scientists are working on extending what we know about past earthquakes beyond recorded human history. This helps. But, accurately predicting earthquakes and their effects requires money, time, and lots of excruciatingly detailed work.

So what do you do when you feel the jolt of an earthquake? In Chile dive for cover, your building will probably still be standing once the shaking stops. In Haiti, it’s down to luck, and the odds are against you. If you’re anywhere near water, don’t wait for warning sirens, head for the hills as fast as you can.

Lindsay Schoenbohm is an Associate Professor of Earth Sciences in the Department of Chemical and Physical Sciences at the University of Toronto, Mississauga.