Transcript 8.1 Earthquakes 8.2 Measuring Earthquakes

Starter 11/18/14
1. What evidence is there for plate
tectonics?
2. The Earth is currently in ______
polarity.
3. Deep focus earthquakes are
associated with ocean ______.
4. Why do the tectonic plates move?
Starter
8.1 What is an Earthquake? P. 74
http://geographysite.co.uk/pages/physical/earth/i
mages/plates.gif
Today, you will be able to:
• Compare/contrast the epicenter and focus of an earthquake.
• Identify the cause of earthquakes.
• Compare and contrast aftershocks and foreshocks.
Vocabulary (Index Cards)
132.Earthquake
133.Focus
134.Epicenter
135.Fault
136.Aftershock
137.Foreshock
138.Seismograph
139.Seismogram
140.Surface wave
141.S wave
142.P wave
What type of plate boundary
causes earthquakes?
• Transform fault
What Is an Earthquake?
 An earthquake is the vibration of Earth
produced by the rapid release of energy
 Focus and Epicenter
• Focus is the point in Earth (under the crust)
where the earthquake starts.
• Epicenter is the location on the surface directly
above the focus.
 Faults
• Faults are fractures in Earth where movement
has occurred.
•Fault creep- the slow, gradual, smooth fault
movement
Focus, Epicenter, and Fault
Slippage Along a Fault
What Is an Earthquake?
 Elastic Rebound Hypothesis
• Most earthquakes are produced by the rapid
release of elastic energy stored in rock that
has been subjected to great forces.
• When the strength of the rock is exceeded, it
suddenly breaks, causing the vibrations of an
earthquake.
•Seismic wave- energy that radiates in all
directions from the earthquakes origin
(starting point = focus)
Elastic Rebound Hypothesis
What Is an Earthquake?
 Aftershocks and Foreshocks
• An aftershock is a small earthquake that occurs
after the main earthquake.
• A foreshock is a small earthquake that occurs
before a major earthquake (can happen years
before a major earthquake).
8.2 Measuring Earthquakes p. 74
http://geographysite.co.uk/pages/physical/earth/i
mages/plates.gif
Today, you will be able to:
• Identify the three types of seismic waves.
• Explain how to locate the epicenter of an earthquake.
• Identify other dangers associated with earthquakes.
• Explain the potential for earthquake prediction.
Measuring Earthquakes
 Seismographs are instruments that
record earthquake waves.
Seismo=shake
 Seismograms are traces of amplified,
electronically recorded ground motion
made by seismographs.
 Surface waves are seismic waves that
travel along Earth’s outer layer.
Most destructive waves
Seismograph
Seismogram
Measuring Earthquakes
 Body Waves
• Identified as P waves or S 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 (speed) of
all earthquake waves
Measuring Earthquakes
 Body Waves
• S waves
- Seismic waves that through Earth’s interior
- Shake particles at right angles to the direction
that they travel
- Travel only through solids
- Slower velocity than P waves
 A seismogram shows all three types of
seismic waves—surface waves, P
waves, and S waves.
Seismic Waves
Measuring 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
Measuring Earthquakes
 Historically, scientists have used two different
types of measurements to describe the size of an
earthquake  intensity and magnitude.
 Intensity = amount of shaking based on damage
 Magnitude =measure of the size of seismic waves
 Richter Scale
• Based on the amplitude of the largest seismic wave
• 5.0 is 10x greater than 4.0
• Does not estimate adequately the size of
very large earthquakes
Measuring Earthquakes
 Momentum Magnitude
• Derived from the amount of displacement
(movement) that occurs along the fault zone
• Moment magnitude is the most widely used
measurement for earthquakes because it is the
only magnitude scale that estimates the energy
released by earthquakes.
• Measures very large earthquakes
Earthquake Magnitudes
Some Notable Earthquakes
NC Seismic Activity
• Earliest record earthquake activity March
8, 1735
• Earthquakes in Missouri were felt
throughout NC in 1811
• East coast earthquakes felt over a larger
area because east coast made of older
rock that has not been fractured
Post-Test (page 64)
1. In what order do the basic types of
seismic waves reach a seismograph?
2. Describe the differences in speed and mode
of travel between primary (P) waves and
secondary (S) waves.
3. Write a paragraph describing in your own
words an earthquake that has been
measured as a moment magnitude of 6.0.
Seismic Risk Map (page 61)
Use Textbook to identify states p.
744
Pangaea Puzzle (page 57)
Red
Blue
Yellow
Pink
Orange
Purple
Green
Pangaea Puzzle (page 57)
Earth’s Layers Foldable (page 59)
Plate Boundaries (page 61)
Plate Boundaries (page 61)
Plate Boundaries (page 61)