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Fierce Science: MAGNITUDE!!! Understanding Jessicas (aka Earthquake Scales)

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A blogumn by Tabitha Esther

When an earthquake happens, all you hear on the news is “Magnitude 6.7 on the Richter scale”, but what exactly is the Richter scale? Who is this Richter that we are trusting to tell us how big an earthquake was? Why not just call it the Jeff scale or the Diane scale? Truth is, there are several flavors of magnitude scales when it comes to earthquakes. Let’s learn about them, shall we?

To make this easier to understand, I will compare each magnitude scale to an actress with the first name of Jessica.

Richter Magnitude = Jessica Lange: The stalwart scale we all know and love.  A little outdated, but useful nonetheless. You see, Charles Richter and Beno Guttenberg were fancy-pants geophysicists at CalTech in the early part of the 20th century. They built something called a Wood-Anderson seismograph.

Note:

SEISMOGRAPH = THE INSTRUMENT
SEISMOGRAM = THE PIECE OF PAPER WITH THE SQUIGGLES ON IT

To report an earthquake’s magnitude on the Richter scale, you would have to record the earthquake on a Wood-Anderson seismograph at exactly 100km (about 60 miles) from the earthquake. A little inconvenient, but it worked for earthquakes in and around Southern California at the time of its invention.

A Wood-Anderson seismograph can only record earthquakes up to about a 6.8. Bigger than that and the mechanisms inside go all screwy and you don’t get a good record of the event. Boo.

Duration Magnitude = Jessica Alba: Fails to deliver consistent results. This scale deals with how long an earthquake lasts. The duration of an earthquake in any one location depends on what’s going on with the geology beneath you. An earthquake will last longer if you’re standing in a basin filled with sand (*cough*cough*Los Angeles*cough*) than if you are standing on good, solid bedrock. This magnitude scale had its fifteen minutes of fame after the 1999 earthquake in Izmut, Turkey, but it has since gone out of style.

Moment Magnitude = Jessica Biel: This is the more popular form of magnitude these days. Moment Magnitude scale relies on something called the seismic moment of an earthquake which takes into account the area of the fault that slipped and how much the fault was displaced. No messy seismograms, no instructions on where to record the earthquake. Just quantities that are physically measurable. Nice.

Body/Surface Wave Magnitude = Jessica Simpson:
You can live without these.

See. Now you know about magnitude scales. Go forth and impress your friends with SCIENCE!

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Photo Credit: drinksmachine/flickr.com