Fwd: Krampf #408 Richter Scale

From: John or Jan Lahr (JohnJan@lahr.org)
Date: Mon Jan 03 2005 - 09:29:03 PST

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Date: Mon, 03 Jan 2005 10:29:03 -0700
From: John or Jan Lahr <JohnJan@lahr.org>
Subject: Fwd: Krampf #408 Richter Scale 

From: KRAMPF@aol.com
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Date: Mon, 3 Jan 2005 11:43:20 EST
Subject: Krampf #408 Richter Scale

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This Week's Experiment - #408 Richter Scale

I hope you all had a wonderful holiday season and are having a happy new
year.   I had a very nice visit to Memphis, and now I am on my way to Miami to do
more science shows for Florida Power and Light.   After the ice and freezing
temperatures I found in Memphis, the warmth of Miami will be a big change.

I am sure that many of you are wondering about the cake and Jello that I
mentioned last week.   I intended to write more about earthquakes, but the e-mail
very quickly got too long.   I decided to save half for this week, but forgot
to change the materials list.   This week, you will need:

a large plate
cake
Jello or something similar

Anytime there is an earthquake, the news media makes a big point of talking
about the Richter Scale, using it to indicate how bad the earthquake was.   As
we will see, the Richter Scale does not tell us nearly as much about surface
effects as people think it does.   Instead, it tells us how much energy was
involved in the quake.   That may seem like a small point until you think about
it for a minute.   An earthquake from a fault that is deep in the Earth may not
cause as much damage as an earthquake from a fault at the surface, even if
they release the same amount of energy.  

Even at the same depth, there are other things that can cause major
differences in the surface effects of an earthquake.   Place a large, dinner plate on a
flat surface.   Cut a square of cake and place it on one side of the plate.  
Cut a square of Jello the same size and place it on the other side of the
plate.   Imagine that the plate is part of the crust of the Earth.   (Insert your
own joke about plate tectonics here.)   Then imagine a tiny city built on top
of each of the two squares.   Shake the plate from side to side to simulate
an earthquake.   Which of the cities do you think would have the most surface
effects?

Think of the city on the cake as a city built on solid rock, while the Jello
represents a city built on layers of sand, gravel and clay.   With the same
amount of energy, differences in geology can give you very different results.

Another thing that many people don't realize about the Richter Scale is that
it is a logarithmic scale.   WAIT!   Don't run away!   I promise to keep this
simple.   Because the intensity of earthquakes varies so much, they use a
logarithmic scale to make it manageable.   It simply means that the vibrations of
an earthquake with a 3 rating are ten times stronger than for one with a
rating of 2.   A 4 is ten times stronger than a 3, and so on.   If you look at the
total energy, it gets even more impressive.   Because the energy radiates in
all directions, the energy difference between each number on the scale is more
than 30 times greater.   That means that while the vibrations of a 4 are ten
times stronger than a 3, the total energy released is more than 30 times
stronger!  

This means that as you go up the scale, the points become much more
important.   When the news media reported on the recent quake, some said it was a 9,
while others said it was an 8.9.   That does not sound like much difference
until you look at the way the scale works.   The difference between 8.9 and 9 is
bigger than the difference between a 1 and an 8.
 
There is a different scale which is much more useful to the average person.  
The Modified Mercalli Scale is based on surface effects, so it gives you a
much clearer idea of the impact of the quake.   Instead of a single rating for
each earthquake, you get a map with zones to show how much impact it had on
each area.   You can find a copy of the scale at:

http://neic.usgs.gov/neis/general/mercalli.html

I know that it will take a while to digest all this information, so I suggest
you digest the cake and Jello at the same time.  

Have a wonder filled week.

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