Hi:
The Richter method of analyzing earthquakes is based on what can be
learned from a simple seismometer. For example by looking at the time
difference between the P wave and the main shaking you can determine how
far away the epicenter is located. The Richter number depends on the
peak of the main shaking. But the energy depends on the integral of the
magnitude of the shaking over the time it lasts. The damage is
proportional to the total energy not it's peak. The public is used to
hearing the Richter number even though it does not really describe the
damage level.
For example I had just left work when the Loma Prieta quake happened and
was standing in front of the building watching the wall sized windows
oil canning. With each cycle the window displacement was getting
larger. If the quake had lasted about 30 second longer all the windows
would have exploded, either with glass going into the building or coming
at those of us standing in in front. We started to get on the ground to
get some protection, but then the quake stopped.
http://www.prc68.com/I/Seismometer.shtml
Have Fun,
Brooke Clarke
http://www.PRC68.com
William H. Fite wrote:
For meteorologists and geologists, the Richter scale has a carefully defined
meaning and is used only for purposes where that definition fits.
This per a friend of mine who does seismic stuff for NOAA:
Him: The Richter number means something very specific to us and something
quite different to the media. Actually, the Richter doesn't have a great
deal of analytical value to us. You can say, this is a Category Four
hurricane but that really tells you very little about what is going on in
the storm. Richter is like that.
Me: You're saying that the Richter is a poor predictor of surface
disruption?
Him: Well, obviously a 9 will be expected to do much more damage than a 6
but it is at best a very rough indicator. The location of the epicenter and
a dozen other factors play into it.
Me: So how do you assess the damage potential?
Him: Lots of people think we still rely mainly on the old
pendulum-and-stylus seismographs from the 1930s. Actually, we take a great
many measurements in addition to seismometry. But when it comes to
assessing the damage, we go outside and look, just like the TV stations do.
And his final comment: By the way, did you know that when the shuttle
launches we capture that on virtually every strain guage seismometer in the
country?
I found that interesting.
On Thu, Feb 24, 2011 at 10:56 PM, jimlux<jim...@earthlink.net> wrote:
On 2/24/11 5:23 PM, Bob Bownes wrote:
What is the conversion factor for Richter to dBm? :)
Bob
As a guy with degrees in geology and EE. I really should know this...:)
Especially since both are log scales..
The problem is that Richter is log magnitude displacement on a particular
kind of seismometer (which is sort of a low pass filter) and dBm is log
power. However, there should be some sort of scale factor that converts it.
I think it's energy goes as amplitude^1.5. there's also a scale factor for
how far the seismograph is from the epicenter.
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