Earthquakes
Occur on faults, near plate boundaries
Three types of fault:
normal (tension stress),
reverse (compressive stresss),
strike-slip (also called transform) (shear stress)
Elastic rebound theory: elastic strain slowly builds up – then energy released
suddenly
Focus: location of earthquake at depth
Epicenter: point on surface above focus
Seismic waves (km/sec)
1) P-waves (like sound waves) – Primary waves- fastest
2) S-waves (shear waves)-Secondary, slower
S waves cannot travel in liquids (e.g outer core)
3) Surface waves cause most damage
Seismograph – instrument records ground motion
Suspended weight with pen attached
Rotating drum of paper
When earth shakes pen records ground motion
Called a seismogram
Distance to epicenter
Difference in arrival times of P and S waves
Location of epicenter
Need at least 3 seismic stations
Draw circle around each station
Radius of circle is distance to quake
Intersection of 3 circles is location of quake
Earthquake magnitudes
1) Mercalli damage scale: 1 (none) –12 (total)
2) Richter scale – log scale- measures amplitude of ground motion. Each
unit= 30 times more energy.
3) Moment magnitude (best estimate of energy)
= (fault slip x fault area x strength of rock)
Study questions.
Identify the letter of the choice that best completes the statement or answers the question.
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1. What is the map location of an earthquake called?
a. focus
b. ground zero
c. epicenter
d. a bad place to be
e. nexus
2. What is the point of subsurface origin of an earthquake called?
a. focus
b. ground zero
c. epicenter
d. a bad place to be
e. nexus
3. Which type of earthquake wave moves the fastest?
a. P-waves
b. S-waves
c. Love waves
d. Rayleigh waves
e. Permanent waves
4. Which type of earthquake wave could travel through a vacuum?
a. P-waves
b. S-waves
c. surface waves
d. all of the above
e. none of the above
5. Which type of earthquake body wave cannot pass through liquids?
a. P-waves
b. S-waves
c. Love waves
d. Rayleigh waves
e. surface wave
6. How much more energy does a magnitude 8 earthquake release than a magnitude 7 earthquake?
a. 2 times more
b.
c.
d.
e.
10 times more
30 times more
900 times more
27,000 times more
a
Answer Section
MULTIPLE CHOICE
1.
2.
3.
4.
5.
6.
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
C
A
A
E
B
C