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Chapter 8
Earthquakes
Recent Earthquakes
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Kobe Earthquake 07.01.1995
Satellite Photos - Japan Before and After Tsunami - Interactive Feature NYTimes.com
Video of Tsunami - Video Library - The New York Times
Earthquake and Tsunami - Video Library - The New York Times
Day 2: Japan's Earthquake - Video Library - The New York Times
Day 3: Japan’s Nuclear Woes - Video Library - The New York Times
Widespread Devastation in Japan - Video Library - The New York Times
Where do earthquakes
occur?
• On Earth of course
• Seismology is the study of
earthquakes
• Most quakes occur at the edge
of tectonic plates
• Tectonic plates are pieces of
the lithosphere that move on top
of the asthenosphere
Plate tectonics
• Plates push and pull upon one
another
• Faults occur when the crust
breaks
• Breaks occur at the edge of
plate boundaries
What causes Quakes
• The changing of rocks due to stress
is called deformation
• Focus is the area in the crust where
the rock under stress breaks
• Epicenter is the point on Earth’s
surface directly above the focus
Focus and epicenter
Earthquake
Characteristics
Plate
Boundary
Fault type Stress force
Transform
Strike-slip Shearing
Convergent Reverse
Compression
Divergent
Tension
Normal
E-quake Motion
• Seismic Waves
– Waves of energy that travel
through the earth
• Seismic waves classified as:
– P waves
– S waves
– Surface
P and S waves
• Travel through the Earth
• Released from Focus
• When they reach the surface at
epicenter become Surface
waves
P and S Wave
Characteristics
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P waves
Primary wave
Pressure wave
Arrives first
Travels through
solid, liquid or
gas
• 1st wave to be
detected
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S waves
Secondary wave
Shear wave
Arrives last
Cannot travel
through liquid
Surface wave
• Move the ground up and down in
circles
• Travel slower than P and S but
are more destructive
Measuring E-quakes
• Common Methods
– Mercalli
• Rating based upon damage
– Richter
• Rating based upon seismic wave
– Moment Magnitude
• Rating based upon total energy
released
• Used to rate all earthquakes
Earthquake Damage
• Damage occurs due to:
– Shaking
– Liquefaction
• Loose soil turns to mud
– Aftershocks
• Earthquake after larger earthquake
– Tsunamis
• Water displacement