Sunday, January 10, 2010

How Big a 6.5 Earthquake Is Depends On You

Yesterday evening, an earthquake measuring 6.5 on the Richter scale struck off the coast of Northern California, near Eureka.  To refresh your memory, the Richter scale is logarithmic, which means that every increase of 1 on the scale means the earthquake is 10 times more powerful.  So by way of comparison, this earthquake packed about 1/5 the power of the one that struck San Francisco during the World Series in 1989, and about 1/2000 of the one that caused the tsunami in the Indian Ocean the day after Christmas, 2004.  On the other hand, it had more than 30 times the power of the atomic bomb that was dropped on Nagasaki, Japan.

It's hard for your average person to get a good feel for earthquake magnitudes.  The difficult math of a logarithmic scale is only part of the problem, however.  The other big part is what your previous experience with earthquakes has been.

Residents of Eureka have been quoted in the press discussing the earthquake.  Reactions range from the alarmed, as demonstrated by Phil Burns, a cafe owner in Eureka, who said, "It was a monstrous one," to the more relaxed Cole Machado, who told CNN, "I thought my TV was going to fall over."  There are also those who try to explain how the earthquake felt, like Chris Durant, a reporter who explained, "We are used to feeling small ones, but after the first few seconds, we looked at each other and said this is not a small one."  Jessica Tucker of Ferndale said, " "It rolled and rolled and then it slammed."

Notably, none of these people were experiencing their first earthquake.  This is important for two reasons.  First of all, they all have a frame of reference.  They talk about this one in relation to other ones, and they have vocabulary with which to describe it.  Second, not one person I've come across said they were afraid they were going to die.  Believing you are going to die is a strong predictor of post traumatic stress and PTSD, so this is a good thing.

Compare this to what would have happened if a 6.5 earthquake hit in, say, Boston, where a "big one" might be 3.0.  First of all, the damage would have been much more severe, because Boston is not built for earthquakes the way California is.  But the fear would also be much more severe, solely based on the earthquake without the damage, because most people in Boston have never been in an earthquake of any remarkable size.  The reactions we are hearing out of California probably compare to what we would hear from Boston in a 5.5 or 6.0 -- 1/10 to 1/5 the size of this one.  If a 6.5 earthquake hit Boston, people would believe they were going to die, in part because they would be more likely to, and the amount of stress symptoms you would see afterwards would be much higher.

I've been in two sizable earthquakes in my life -- both 5.6 on the Richter sale.  I'm from Boston.  I was scared.  My husband spent his teen years in the San Francisco Bay Area.  It's not that he didn't have a healthy respect for these two earthquakes, but he knew they weren't "big ones" much faster than I did.  Life in California is, in part, about pre-earthquake inoculation.  By experiencing small ones so often, the bigger ones just aren't as terrifying. 


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Naomi Zikmund-Fisher
is a clinical social worker, former school Principal and a Crisis Consultant for schools and community organizations. You can learn more about her at
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