Earthquakes and Richter Magnitude
NAME_______________________________________
A major 8.9 Earthquake just struck about 100 miles off the coast of Japan. As a result a tsunami with a wave
anywhere from two to 12 feet high moving at about 500 miles per hour is sweeping across the Pacific Ocean.
How powerful is an 8.9 magnitude earthquake? The following is a simplified explanation of the Richter scale. It
will help us make some comparisons between earthquakes of various strengths.
More recently, Dr. Hiroo Kanamori came up with a relationship between seismic moment and seismic wave energy. It
gives: Energy = (Moment)/20,000
For this moment is in units of dyne-cm, and energy is in units of ergs. dyne-cm and ergs are unit equivalents, but have
different physical meaning.
Let's take a look at the seismic wave energy yielded by our two examples, in comparison to that of a number of
earthquakes and other phenomena. For this we'll use a larger unit of energy, the seismic energy yield of quantities of the
explosive TNT (We assume one ounce of TNT exploded below ground yields 640 million ergs of seismic wave energy):
Richter
Magnitude
TNT for Seismic
Energy Yield
-1.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
6
30
320
1
4.6
29
73
1,000
5,100
32,000
80,000
1 million
5 million
32 million
7.5
8.0
8.5
9.0
10.0
12.0
160 million
1 billion
5 billion
32 billion
1 trillion
160 trillion
ounces
pounds
pounds
ton
tons
tons
tons
tons
tons
tons
tons
tons
tons
tons
tons
tons
tons
tons
tons
tons
Example
(approximate)
Breaking a rock on a lab table
Large Blast at a Construction Site
Large Quarry or Mine Blast
Small Nuclear Weapon
Average Tornado (total energy)
Little Skull Mtn., NV Quake, 1992
Double Spring Flat, NV Quake, 1994
Northridge, CA Quake, 1994
Hyogo-Ken Nanbu, Japan Quake, 1995; Largest
Thermonuclear Weapon
Landers, CA Quake, 1992
San Francisco, CA Quake, 1906
Anchorage, AK Quake, 1964
Chilean Quake, 1960
(San-Andreas type fault circling Earth)
(Fault Earth in half through center,
OR Earth's daily receipt of solar energy)i
Questions:
1. According to the table what magnitude earthquake releases a similar amount of energy to small
nuclear weapon?
2. Approximately how many tons of energy was released during the March 11th earthquake off Japan?
3. According to the chart, how many times greater is a 5.0 magnitude quake than a 4.0 magnitude
quake?
4. According to the chart, how many times greater is an 8.0 magnitude quake than a 7.0 magnitude
quake? How many times greater is a 9.0 magnitude quake than an 8.0 magnitude quake? See any
patterns? Does this pattern hold roughly hold true in the table?
5. Using the information from the table create a graph that gives the energy yield for any Richter
magnitude. Put Richter magnitude on the x-axis and put energy yield on the y – axis.
6. Approximately how many tons of energy was released during the 2010 earth quake in Haiti (7.1)?
7. Approximately how many tons of energy was released during the 2010 earth quake in Chile (8.8)?
8. Approximately how many tons of energy was released during the 1906 earth quake in San Francisco
(7.9)?
9. Using either your graph or the table write an exponential equation that gives the energy yield for
any Richter magnitude.
10. An earthquake has a seismic energy release of approximately 500 billion tons. About what
magnitude earthquake was this?
Created by YUMMYMATH.com
i
Source: http://www.seismo.unr.edu/ftp/pub/louie/class/100/magnitude.html 3/11/2011