Wednesday, February 27, 2013

Chile: 3 Years after the 27F Earthquake

Mayor earthquakes in Chile since February 27th 2010. (Credit: José Infestas & EMOL)

Three years ago, before I moved to Chile, there was a massive 8.8-magnitude earthquake in the central region. This occurred on the 27th of February 2010 and the event is commonly refer to in the news as 27/F (or variants like 27-F). A few days ago, there was an interesting report on earthquake statistics in Chile, which I would like to summarize (and translate, as it's in Spanish) for you.
Given my current travels this is a scheduled post and I didn't have time to double check all the facts in the report. I'm hoping they are mostly accurate, though that newspaper has had it's share of mistakes in the past. Nevertheless, the important trends still should hold. Now, on to my summary...

It is sometimes easy to forget that one lives in a seismic country. Although there are plenty of earthquakes --- apparently 96 in the region during the month of January, an average of 3 per day --- most are too small to be felt except by the most exquisite of instruments. One can easily be lured in a false sense of security in such circumstances.

Earthquake strength is measured on the Richter magnitude scale. The scale is logarithmic, so an earthquake magnitude 5 is ten times stronger than one of 4. About ten thousand 4th magnitude earthquakes occur each year across the world and these are strong enough to be felt by most people living near them. Magnitude 8.8 earthquakes like the one 3 years ago in Chile are rare --- usually just one a year --- and can cause substantial damage.

Earthquakes are frequently accompanied by aftershocks, smaller earthquakes that occur near the same area as the original one. This was certainly the case in the 27/F event, with a reported 1644 earthquakes taking place in the region during March 2010. The month of March is 730 hours long, which means there were on average 2 earthquakes each hour that year. Naturally, many of these were small and unfelt by humans, but others were stronger.

Over the past 3 years, seismic activity in the area has lessened, but it is still above average levels. Most earthquakes are weak, but a few are significant: 3 magnitude 7th earthquakes and 29 magnitude 6th.
Apparently the region is supposed to experience just under 200 earthquakes (of any magnitude) per year.  In 2012, the region experienced five times as many earthquakes.
This neat infographic (in Spanish) highlights the 3 magnitude 7th earthquakes and summarizes the number in the region over the past 4 years:
Earthquake statistics in Chile's central region. The top panel lists the three magnitude 7th earthquakes since 27F. The borrom left shows the number of earthquakes of any magnitude in the region since 2009. The bottom right panel shows the earthquakes per month since the 27F event. (Credit: José Infestas & EMOL)

Earthquakes can still not be predicted. Do not be misled by people claiming an earthquake will or will not happen, but also don't live your life in constant fear. The best way to deal with earthquakes is to always be prepared. The USGS has plenty of information, but here's a link to the 7 basic steps of earthquake safety.

I have personally felt a few earthquakes here in Chile and during my time in Southern California. However, I have never felt one that was very strong or damaging. I hope I never do, but living in seismic places like these it could just be a matter of time. Maybe I should go back and look at those basic steps again...

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