Download 6.1-6.3 Earthquakes

• Earthquakes: vibrations through earth’s crust
– Occur when rocks under stress slip or shift along a
fault
Normally, rocks are pressed together tightly
= not moving
Or “locked”
Elastic Rebound Theory
• Rocks along each side of a fault are moving
slowly.
• If the rock is “locked”, then stress will increase
• When the rock is stressed beyond its capacity,
the rocks separate, or fracture, at the weakest
point, and then they spring back to their original
position
– As rocks move they create vibrations, called Seismic
Waves
• Aftershocks: series of tremors caused by other
areas adjusting to stress of the initial
earthquake
Focus: place where slip first occurs
Epicenter: The point on Earth’s surface directly
above the focus.
Seismic waves radiate out in all
directions from the focus.
Major Earthquake Zones
Where do earthquakes occur?
• Along or near the edges of lithospheric plates
Journal:
Why do think that earthquakes occur in these
areas? Explain the cause of the earthquakes!
Fault Zones
• Groups of interconnected faults along a plate
boundary
6.2 Recording Earthquakes
• Seismograph: instrument that detects and
records seismic waves
Types of Waves
• The different types of energy waves shake the
ground in different ways and also travel
through the earth at different velocities.
Types of Waves
• P wave: The fastest wave, and therefore the first
to arrive at a given location.
• compression wave, alternately compresses and
expands material in the same direction it is traveling.
• S wave : is slower than the P wave and arrives
next
• shakes the ground up and down and back and forth
perpendicular to the direction it is traveling.
• Surface waves: follow the P and S waves.
Locating an Earthquake
• Scientists analyze the difference between the
arrival of P and S waves .
Journal:
• What instrument measures earthquakes???
Earthquake Measurement
• Magnitude: Measure of energy released
– Described as ground motion
– Measured using the RICHTER SCALE
• Mercalli Scale: describes intensity, or amount
of damage an earthquake causes.
– Scale I – XII
Journal:
• Describe the difference between the Richter
Scale and the Mercalli Scale.
• Reading an Earthquake Wave Graph IN CLASS
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