Chapter 2, Section 2 – Earthquakes & Seismic Waves
**most earthquakes are too small to notice
**forces in plate movement cause earthquakes
**most earthquakes begin in the lithosphere
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II.
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Types of Seismic Waves
a. Sent out from the focus of an earthquake
b. Carry energy away from the focus, through Earth’s interior,
and across the surface
c. Three main types of seismic waves:
i. P waves: primary waves (1st to arrive)
1. compress and expand the ground
2. crust vibrates forward and back along the wave’s
path
3. travel through solids and liquids
ii. S waves: secondary waves
1. vibrate from side to side and up and down
2. ground shake back and forth
3. cannot move through liquids
iii. Surface waves:
1. move more slowly
2. produce more severe/damaging ground
movements
Measuring Earthquakes
a. Three commonly used methods/tools:
i. Mercalli Scale: measures damage done in specific
location
ii. Richter Scale: measures seismic waves of earthquake to
determine earthquake size (magnitude – amount of
energy given off)
iii. Moment-Magnitude Scale: determines the total energy
given off
b. seismograph measures an earthquake’s seismic waves
Locating the Epicenter
a. Use seismic waves to locate
b. Determine distance of epicenter to seismograph, measure
difference between arrival of P waves and S waves
c. Draw circles on map – circle radius is distance from
seismograph to epicenter
i. Point where circles intersect is the epicenter