What is an Earthquake?
What Is an Earthquake?
Earthquake - vibration of Earth produced
by rapid release of energy
• Aftershock - small earthquake after the
main earthquake.
• Foreshock - small earthquake before a
major earthquake.
Anatomy of an Earthquake?
What Causes an Earthquake
Mini Lab – Elastic Rebound Hypothesis
1.Take two blocks and treat them like converging boundaries
2.Take two blocks and treat them like diverging boundaries
3.Take two blocks and treat them like transform fault boundaries
a) Smooth Side – Smooth Side
b) Smooth Side – Rough Side
c) Rough Side – Rough Side
4.Slowly bend the popsicle stick between your thumb and
middle finger until it breaks
Elastic Rebound Questions
1. Did convergent or divergent boundaries ever
result in “catch” between the blocks?
2. Which scenario caused the most “catch”
between the sides of the blocks?
3. How did the potential energy in the stick
change as it was bent?
4. What happened when the potential energy in
the stick was released?
5. Write a hypothesis for the cause of an
earthquake
Elastic Rebound Hypothesis
Rapid release of elastic
energy stored in rock that
occurs when rock is broken
along a transform fault
boundary.
Elastic Rebound Hypothesis
Slippage Along a Fault
Earthquake Waves
During an earthquake, energy is released in the
form of waves.
P Waves
S Waves
Surface Waves
Earthquake Waves
P waves
Are push-pull waves that push (compress) and pull
(expand) in the direction that the waves travel
Travel through solids, liquids, and gases
Have the greatest velocity of all earthquake waves
Earthquake Waves
S waves
Seismic waves that travel along Earth’s outer layer
Shake particles at right angles to the direction of
travel
Travel only through solids
Slower velocity than P waves
Earthquake Waves
Surface waves
Seismic waves traveling along Earth’s surface
Slowest of the seismic waves
Questions About Earthquake
Waves
1. An earthquake occurs 100 miles away. In
what order will the waves arrive at your
location?
2. Which waves do you think are most
dangerous? Why?
3. Suggest how earthquake waves have been
used to develop our model of the Earth’s
interior? Think about what the inside of
Earth looks like.
Locating Earthquakes
Earthquake Waves
Seismographs are instruments that record
earthquake waves.
Seismograms are traces of amplified, electronically
recorded ground motion made by seismographs.
Locating Earthquakes
 Earthquake Distance
• The epicenter is located using the difference in
the arrival times between P and S wave
recordings, which are related to distance.
 Earthquake Direction
• Travel-time graphs from three or more
seismographs can be used to find the exact
location of an earthquake epicenter.
 Earthquake Zones
• About 95 percent of the major earthquakes
occur in a few narrow zones.
Locating an Earthquake Lab
Measuring Earthquakes
Richter Scale
Earthquake Severity
Richter
Magnitudes
Less than 3.5
Earthquake
Effects
Generally not felt, but recorded.
3.5-5.4
Often felt, but rarely causes damage.
Under 6.0
At most slight damage to well-designed buildings.
Can cause major damage to poorly constructed buildings
over small regions.
6.1-6.9
Can be destructive in areas up to about 100 kilometers
across where people live.
7.0-7.9
Major earthquake. Can cause serious damage over larger areas.
8 or greater
Great earthquake. Can cause serious damage in areas several
hundred kilometers across.
Mercalli Scale
Estimating Earthquake
Intensity Lab