The opening lines in an old issue of National Geographic are remembered by our CEO as saying "With a force 1,000 times greater than the atomic bomb over Hiroshima......". 

 

This quote was in regard to the Mexico City quake in 1985.  However, even people who read that article probably felt that this was in part because of the special circumstances of that quake.  In that instance, the frequency of the quake itself so closely matched the frequency or "period" of many structures in Mexico City that it caused very destructive resonance.  In more understandable language, that could be described as a situation where the buildings and quake forces joined together and hummed like a tuning fork, thus contributing to more building collapse, and more death.

 

Those special circumstances aside, it's important to consider that just because a person, building or community has survived other quakes in the past, they may not do as well in the future.  Overall magnitude is only part of it, but there are also issues like how close one is to the epicentral area, soil type, and a number of other factors.

 

But magnitude plays a big role, and the changes in energy are more dramatic than most people want to believe.  Higher magnitude quakes also mean longer duration quakes.

 

Unfortunately, the comparison with the nuclear attack on Hiroshima is not ill-founded.  The yield of "Little Boy" which was the nickname of the bomb over Hiroshima, at the close of World War II, was the equivalent to about 15,000 tons of TNT.  According to one source, one ton of TNT releases about 640 million ergs of seismic wave energy underground.   So look at the following equivalency information:

 

     "Little Boy" - 15,000 tons of TNT

     Northridge earthquake, 1994 - 5 million tons TNT

     San Francisco, 1906 - 1 billion tons TNT

     Great Sumatran quake, 2004 - 32 billion tons TNT

 

The latter quake is the one that caused the tremendous tsunamis that killed over a quarter of a million people in multiple countries.  It caused the entire earth to wobble on its axis, and sped up the rotation of the earth, causing effects as much as 10,000 miles away.  And it was only one third of that fault structure.

 

A moderately high magnitude quake like Northridge still tossed people around in the epicentral area.  When the San Andreas goes, some people will actually be thrown into the air, especially if they are unlucky enough to be right on top of the fault.   Distance often helps mitigate these effects, but not always.  Therefore, the two most important things for you to remember from this page are:

 

1) Take preparedness seriously and do not rest on historic attitudes and assumptions, and

 

2) Remember that the terrific forces involved in high magnitude quakes will launch all the contents of every room in your home, school or office around at great speed, if they are not tied down with adequate seismic restraints.  This is a major source of human injury, not just economic damages.

 

It's up to you what you choose to do to prepare, but in our minds, seismic anchoring should definitely be on the "to-do" list of every thinking person who lives in earthquake country.  We also recommend that parents and concerned citizens look around their local schools on this issue.  Based on what we've seen, and what we think you will find in many schools, the probability of direct injuries to children, and blocked exits, etc. from non-anchored equipment and furniture, will (and should) scare you.  The question is this:  How are responsible citizens and our communities going to work together to reduce these risks?