Earthquakes
Earthquake - vibrations in the ground that result from movement along
faults or breaks in Earth’s lithosphere (can occur at all 3 boundaries)
Fault - Fracture in Earth’s Crust
Focus - point BENEATH Earth’s surface where earthquake originates
Epicenter- point ON THE SURFACE where the Earthquake originates (Directly
above focus)
Tsunami- Underwater earthquake that creates a seismic sea wave
Aftershock - a smaller earthquake following the energy of a larger
earthquake
Seismic Waves- carry energy of an earthquake away from the focus
1. Primary Waves (P Waves)
● Longitudinal - Compress & Expand
● Arrive first
● Fastest
● Travel through liquids and solids,
2.
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Secondary Waves (S Waves)
Transverse - move side to side like an S shape
Arrive Second
Slower than P waves
Travel through solids
3.
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Surface Waves (L Waves)
Slowest Wave
Moves up and down like an ocean wave
Most Destructive
Seismograph - Device that records ground movements caused by seismic waves
Magnitude - How we measure an earthquake’s energy, the greater the magnitude, the
greater the energy
How to find an earthquake's epicenter: Use data from AT LEAST THREE seismographs
to determine the distance the waves travel. Where all 3 circles meet = epicenter
Earthquakes and Seismic
Waves
– Occur mostly at boundaries of tectonic plates
– As plates move the edges of the plates
experience tremendous pressure.
– As rocks break energy is released as seismic
waves.
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Seismic waves would have the
most energy at point A
because they have traveled
the least distance to this point.
The focus of an earthquake is the area beneath the surface where
rock begins to break or move.
The epicenter is the point on the surface directly above the
focus.
There are 3 main categories of seismic waves.
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The first waves to arrive are primary waves or
compress and expand the ground.
P waves that
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Secondary waves or S waves vibrate from side to side.
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When P waves and S waves reach the surface, they may become
surface waves (also called L waves)which move the ground like
ocean waves.
Draw lines from the wave to the type of movement on page 233.
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The magnitude , or size, of an earthquake is measured on a seismograph
using the Richter scale or the moment magnitude scale.
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The Richter scale is based on the size of the earthquake’s waves.
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How Do Seismographs Work?
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Seismic waves cause a simple seismograph’s drum
to vibrate and the pen records the drum’s vibrations.
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The pattern of lines is called a seismogram.