
Seismologists use two scales when
classifying earthquakes.
1) Richter Scale
2) Modified Mercalli Scale
 Measures the Magnitude of an earthquake on a ten (10)
point scale.
 In 1935, Charles Richter introduced the concept of
earthquake magnitude.
 Richter magnitude is determined by measuring the largest
amplitude (wave height) recorded on the seismogram.
 Largest recorded
earthquake had a
Richter magnitude
equal to 8.6
Magnitude: measure of the strength of an earthquake
Wave amplitude increases tenfold (10X) with each
increase in Richter magnitude.
 Each increase in 1 in Richter Magnitude represents a
10 fold increase in the wave amplitude (height).
 A magnitude 7 earthquake measures 10 times more
amplitude than a magnitude 6 earthquake.
 A magnitude 8 earthquake measures 10 x 10 (or 100 times)
more amplitude than a magnitude 6 earthquake. And so on.
measures the strength of the ground
Richter scale 
motion
•
10 for each level.
Based on a factor of _____
•
10 times as strong as a
A magnitude 3 is ____
magnitude 2.
•
A magnitude 4 is _____
100 times as strong as a
magnitude 2.
•
How much stronger is a magnitude 7 than a
magnitude 4?
4  5  6  7
x10
x10
x10 = 1,000 times
stronger
• Lag Time:
• The difference in arrival time between the P-wave
and the S-wave.
• How is it calculated?
• ∆T (S-P)
• What is amplitude?
• The maximum vibration (height) from equilibrium.
• measured from zero
1. Label the beginning of the P-wave on the seismogram.
2. Label the beginning of the S-wave on the seismogram.
3. What is the lag time? _______
4. What is the amplitude? ______
5. What was the estimated magnitude? _______
Haiti
earthquake
List of greatest
magnitude
earthquakes
 Measures the Intensity of an earthquake on a twelve
(XII) point scale.
 In 1902 G. Mercalli developed a fairly reliable intensity
scale which assesses the damage to various types of
structures at a specific location.
 Note that earthquake intensity is determined by
several factors including:
1) Strength of earthquake
2) Distance from epicenter
3) Nature of surface materials
4) Building design
• Intensity: measure of the degree to which an
earthquake is felt by people and the amount of damage
caused by the earthquake
• Modified Mercalli Scale
• I to XII (eyewitness accounts)
 The Mercalli scale does not give a true indication of the
actual strength of an earthquake because the amount of
damage done to different places will largely depend on,
the type of materials used and the degree of
construction of buildings and structures.
EARTHQUAKE DOMINOES
3 minutes
End

Use the information on the worksheet to
determine the Mercalli Intensity Scale for
each zip code

Place a
on the map where you think
the epicenter is located.

Answer all worksheet questions
II-III
VIIVIII
V
VI
VI
IX
IX
VI
IX
IV
V
VIIVIII
V
II-III
IV
Identify the Richter Scale Magnitude of the earthquake?
Las Vegas Seismic Station
1.
What is the S-P lag time?
2.
What is the distance to the earthquake
epicenter?
3.
What is the S-wave amplitude?
4.
What is the magnitude using the nonogram?
6.7