With all the earthquakes we have been experiencing lately people are trying to get a sense of just what the difference is between a magnitude 5.5 and a magnitude 6.0. Like many things in science it’s not exactly a simple thing to answer. I decided to hit the web and look around on sites. I hit the USGS, Ask.com, Google, as well as several university sites that do seismic work.
To put it as simply as I can we will start with what an earthquake is. When the plates that make up the upper levels of our planet push together they bind up and create unbelievable pressure. Eventually those two seemingly unmovable forces build up enough pressure that one of them snaps and a massive section of rock plows past the other. To get the idea of what that snap means, imagine a firework blowing up right next to you. That booming concussion that you would feel is exactly what happens deep below the earth’s surface.
The concussion from the snap is energy, and as it moves through the earth from rock to rock it creates a moving wave of vibrating energy.
Now, how does that rolling wave of energy get measured? A seismograph records the vibrations onto a rotating drum and that etching is looked at and points on the wave are measured to provide a measurement of the energy expended by the quake. The Scripps Institute has a cool interactive demonstration that allows you to get a quick feel for how the numbers come together at different points to give you a final number.
We have all the basics out of the way, here is the deal with understanding what magnitude really means. I hate math so this next part is a little tough to get my head around. When looking at magnitude the only way to put the measurement into a manageable format is to use something called a logarithmic scale. The reason being, the amount of energy increases so fast as it travels through the earth the numbers would be too huge to really understand.
The Richter scale grows by powers of 10. An increase of 1 point means the strength of a quake is 10 times greater than the level before it. Here’s how it works: An earthquake registering 2.0 on the Richter scale is 10 times stronger than a quake registering 1.0. A quake registering 3.0 is 10 X 10 or 100 times stronger than a quake registering 1.0 A 4.0 is 10 X 10 X 10 or 1,000 times greater than 1.0 and so on.
Get it— An increase of 1 point means the strength of a quake is 10 times greater than the level before it . That line is key to understanding it.
Finally, if you managed to read all the way to the bottom, here are a couple of Final Jeopardy answers for you.
- The largest earthquake ever measured was in Chile. May 22, 1960 the quake struck measuring 9.5.
- It’s estimated that the meteor that hit the Gulf of Mexico and may have ended the reign of dinosaurs on the planet was a 13 on the Richter scale.
- The Richer scale is a measure of amplitude not damage. Not every 6.0 quake does the same kind of damage. The depth of the quake as well as the kind of bedrock and soils all combine to lessen or intensify the damage.
- The impacts of the planes as well as the final collapse of both World Trade Centers were recorded on a seismograph located 21 miles north of New York City.