Transcript The Richter Scale: Obsolete?

The Richter Scale: Obsolete?
Misconception 2
Geology 101, Fall 2012
Richter scale
• Charles F. Richter at
Caltech developed the
Richter scale to describe
earthquake strength in
1934.
• The deflection
(maximum movement)
of the pen on the
seismograph was used
to determine
magnitude.
Logarithmic scale for earthquakes
• Richter realized that
earthquakes varied widely
in strength, and to keep the
numbers small, he used a
logarithmic scale.
• For instance, if the
seismograph pen moved 1
mm, that was a magnitude
3 quake; if the pen moved
10 times as much (1 cm),
that was a magnitude 4
quake and so forth.
Shortcomings of the Richter scale
• Richter realized that distance
reduces earthquake intensity,
so for distant earthquakes, he
developed a nomograph to
account for distance reducing
the pen movement.
• Worse, southern California,
where Richter worked, had
shallow earthquakes that had
energy characteristics
(slightly) different than many
quakes around the world
because different rocks
transmit quake energy
differently.
Moment magnitude (M) scale
• Hiroo Kanamori and others
at Caltech in the 1970s
developed a logarithmic
scale to describe
earthquake energy output
that depended on knowing
factors such as rock
strength, area and amount
of fault movement.
• This is considered to be a
much better scale to
determine earthquake
energy output.
References
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McCalpin, James P. Appendix 1: Earthquake Magnitude Scales. In James P.
McCalpin (ed.), Volume 95: Paleoseismology. 2nd edition. Retrieved from
http://www.elsevierdirect.com/companions/9780123735768/casestudies/01~App
endix_1.pdf
First slide image: Hargrove, Brantley (August 7, 2012). Connection Between
Quakes and Underground Frack-water Disposal Looks Solid. In Dallas Observer.
Retrieved September 30, 2012, from
http://blogs.dallasobserver.com/unfairpark/2012/08/connection_between_quake
s_and.php
Second slide image: South Dakota Geological Survey (n.d.).Richter Scale Graphic
Representation. In Earthquakes in South Dakota(1872-2012). Retrieved September
30, 2012, from
http://www.sdgs.usd.edu/publications/maps/earthquakes/rscale.htm
Third slide image: US Geological Survey (July 12, 2012). Earthquake Glossary –
Richter Scale. In Earthquakes. Retrieved September 30, 2012, from
http://earthquake.usgs.gov/learn/glossary/?term=Richter%20scale
Fourth slide image: No author (n.d.). 11.8 How Are Earthquakes Measured? In
Lecture 11 – Deformation of Rocks. Retrieved September 30, 2012, from
http://gomyclass.com/geology10/files/lecture11/html/web_data/file75contents.ht
m