1. Measuring Earthquakes
NCES: 6.E.6.2 & 6.E.6.4
Kim Lachler
Updated 10/14

2. Measuring Earthquakes
Seismogram
Instrument used to measure the strength and location of earthquakes
Seismograph
The paper that comes out of a seismogram showing the waves.

3. Measuring Earthquakes
Focus
The point inside the earth where movement along a fault first occurs and energy is released
Epicenter
The point on the earth’s surface located directly above the focus
Focus

4. Types of waves Primary (P waves)
cause rock to move back and forth in the same direction
Go to

5. Types of waves Secondary (S waves)
cause rock to vibrate at right angles to the direction the waves are moving
Go to

6. Types of waves Love (L waves/surface)
slowest, largest, most destructive waves
Go to

7. Wave timing
By reading several different seismograms in different locations the location of the focus/epicenter can be determined.
This is done by looking at what time the P-S waves arrive times and triangulating.

8. Scales
Richter scale
Based on the seismic graph using logarithms to calculate
It is objective, calculating the amount of energy released
Not easy to understand

9. Scales - Richter
A reading of 5 indicates a disturbance with ground motion 10 times as large as a reading of 4.
The energy released increases by a factor of 30 for every unit increase on the Richter scale.
The strongest quake since 1900 was on May 22, 1960 in Chile. It scored a 9.5 on the Richter scale.

10. Scales
Mercalii Scale
It is subjective and varies from location from the epicenter
Easy to understand

11. Scales- Mercalii I Felt by very few people; barely noticeable.
II Felt by a few people, especially on upper floors.
III Noticeable indoors, especially on upper floors, but may not be recognized as an
earthquake.
IV Felt by many indoors, few outdoors. May feel like heavy truck passing by.
V Felt by almost everyone, some people awakened. Small objects moved. trees and poles
may shake.
VI Felt by everyone. Difficult to stand. Some heavy furniture moved, some plaster falls.
Chimneys may be slightly damaged.
VII Slight to moderate damage in well built, ordinary structures. Considerable damage to
poorly built structures. Some walls may fall.
VIII Little damage in specially built structures. Considerable damage to ordinary buildings, severe
damage to poorly built structures. Some walls collapse.
IX Considerable damage to specially built structures, buildings shifted off foundations. Ground cracked
noticeably. Wholesale destruction. Landslides.
X Most masonry and frame structures and their foundations destroyed. Ground badly cracked.
Landslides. Wholesale destruction.
XI Total damage. Few, if any, structures standing. Bridges destroyed. Wide cracks in ground. Waves
seen on ground.
XII Total damage. Waves seen on ground. Objects thrown up into air.

12. Bibliography
Holt, Rinehart & Winston, North Carolina, Holt, Rinehart & Winston, Orlando, Fl, 2005
USGS, earthquakes accessed 10/04/10
Earthquakes, accessed 10/04/10
Ammon, J., Charles, Seismic waves & Earth’s interior accessed 10/7/10
The university of Liverpool, The scales for measuring earthquakes, accessed 10/7/10
How stuff works, How does a seismograph work? What is the Richter scale?, accessed 10/7/10
MichiganTech, Modified Mercalli Intensity Scale, accessed 10/7/10
ABC, Earthquake, accessed 10/7/10