Download Chapter 9: Earthquakes

Chapter 19: Earthquakes
I. Forces Inside Earth
A. Causes of Earthquakes
1. stress of pressure is put on rocks
2. The rock layers bend until they reach their elastic limit
3. Once their limit is exceeded the rocks break
a) fault: a break or crack in a rock where movement occurs
4. This breaking produces vibrations called earthquakes
B. Forces in the Earth
1. Compression: forces or stress that squeezes or compresses
2. Tension: stress that causes stretching & elongation
3. Shear: forces that causes slipping
a) causes rocks on either side of a fault to move past each other
C. Types of Faults
1. Normal Fault
a) Tension pulls the rocks apart
b) Rock above the fault surface moves downward in relation to
rock below the fault surface
c) Dia.
2. Reverse Fault
a) Compression Pushes on Rocks from opposite directions
b) Rocks above the fault surface are forced up & over rocks below
the fault surface
c) Dia.
3. Strike-Slip Fault
a) Shear forces cause rocks to slide past each other
b) rocks on either side of the fault are moving past each other
without much upward or downward movement
c) Ex. San Andreas Fault, CA
d) Dia.
4. Earthquakes occur as pressure builds up in these faults and the rocks
finally break.
II. Earthquake Information
A. Types of Seismic Waves
1. Seismic Wave
a) Energy waves generated by an earthquake
2. Focus
a) point on the Earth’s surface where seismic waves start
b) place where the energy is released
c) Epicenter- point on the Earth’s surface directly above the focus
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3. Primary Waves (P-waves)
a) cause particles & rocks to compress & stretch apart in the same
direction of the wave.
b) can travel through solid, liquid, & air
c) the fastest wave 6km/sec or 21,600km/hr or 12,960mph
4. Secondary Waves (S-waves)
a) cause rocks to move at right angles to the direction of the wave.
b) can only travel through solids
c) second fastest wave 3.5km/sec or 12,600km/hr or 7560mph
5. Surface Waves
a) surface waves start at the epicenter
b) the waves move up & down & side to side
c) Ex. L-wave: move up and down
d) slowest wave 2.0km/sec or 7200km/hr or 4320 mph
B. Locating an Epicenter
1. Seismograph Station
a) records the arrival of earthquake waves
b) P-waves arrive 1st, S-waves second
c) P-S wave graph pg 501
2. How to locate an epicenter
a) 3 stations are needed
b) the distance from the Earthquake is used to find the epicenter
C. Mapping Earth’s Interior
1. Inner Core
a) Solid Dense
b) composed of Iron and Nickel
2. Outer Core
a) Liquid
b) composed of Iron & Nickel
3. Mantle
a) Is directly above the outer core
b) the largest layer in the Earth
c) composed of silicon, oxygen, magnesium, & iron
4. Crust
a) Outermost layer of the Earth
b) separated from the mantle by the Moho Discontinuity
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5. Moho Discontinuity
a) layer that lies between the crust and the upper mantle
b) P & S wave slow down because this layer is partially melted
c) was discovered by Andrija Mohorovicic
6. Shadow Zone
a) located 105o to 140o from the focus
b) no earthquake waves are detected there
c) liquid outer core prevents S-waves from going through the Earth
d) P-waves slow down & are deflected away fro the outer core
e) pg 250 Fig. 9-9
III. Destruction by Earthquakes
A. Measuring Earthquakes
1. Seismology
a) seismologist: scientist who studies earthquakes
b) seismograph: records primary, secondary, and surface waves
B. Earthquake Magnitude
1. Richter Scale
a) describes how much energy is released by an Earthquake
b) Each degree of magnitude is 32 times greater than the one
before
c) 5.5 – 6.5 = 32 times stronger
5.5 – 7.5 1025 times stronger (322)
2. Moment magnitude Scale
a) looks at fault size
b) measures how much movement occurred
c) how stiff are the rocks?
d) the number is an average of several seismic waves
3. Modified Mercalli Scale
a) Measures the amount of damage
b) I (little damage) XII (total destruction)
4. Depth of Focus
a) Ranked as shallow, intermediate or deep
b) devastating earthquakes are always shallow focus
C. Tsunamis (Tidal Wave)
1. Caused by an Earthquake under the ocean
2. The quick movement pushes against the water creating a powerful wave
3. These waves can be over 30m (80ft) high when they reach the surface.
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*You must also know your vocabulary.
* The test will contain several application style questions.
*There will be some open-ended questions also for completion (these are worth more)
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