Chapter 15
Earthquakes
Earthquakes and Plate Tectonics
• Objectives
– Explain how earthquakes result from the buildup of stress in
earth’s crust
– Control normal, reverse, and strike-slip faults
Cause of Earthquakes
• Rocks similar to _________ band
• Rocks move and break along surfaces called __________.
• On each side of the fault rocks move in ______________
directions
• What causes rocks to move?
– Plate _______________
• When plate move, __________ builds up on rocks
• To relieve stress rocks tend to
–
–
–
• If force is to great the rock breaks
– Causes vibrations (_______________)
Types Of Faults
•
Most earthquakes occur along tectonic plate
______________
80% of all occur along _____________ Plate
•
•
1. Normal Faults – Rocks are subject to the force of
___________
-
Occurs at ___________ boundaries
Rocks above Fault surface move __________
Rocks below move __________
-
Theses types of faults occurred during the formation of the
_________________
2. Reverse Fault
- ___________________ forces are applied
- Rocks above fault surface are forced ______
- Rocks below are forced __________
-Generated at a ______________ boundary
- ________________ Mountains contain many reverse
faults
3. Strike-Slip Fault
- ______________ Fault
-Each plate sliding __________ one another
-Subject to _____________ forces
- Rocks moving in different but not opposite directions
- Most famous _______________ Fault
- North American Plate and Pacific Plate
Seismic waves
• Generated by an earthquakes ____________
• Moves ____________ from the focus
• Three types of waves
•
1. Primary
-
Cause rock particles to move ____________ and fourth
Move the ___________
Slow down when they reach asthenosphere
Slowed but can travel through the liquid outer core
2. Secondary
- rock particles move at ____________ angles
- ____________ then primary waves
- Cannot travel through ______________
- cannot move through the ______________ core
3. Surface Waves
- originates at the _________________
- gives particles _____________ motion
- cause most of the _________________
- similar to waves in a___________ or in the ocean
- are the _______________ of the three waves
-
Locating an Epicenter
• Seismic Waves are measured at ________________
stations
• Primary waves arrive _____________
• Secondary – ______________
• Surface – _________________
• The farther ____________ the waves the farther the
epicenter is
• ____ seismographs stations are needed to determine an
epicenter
• Distance btw. The station and the ___________ is
determined
• Scientist draw _________ around each station
• Where the three circles _____________ is the epicenter
Mapping the Interior of Earth
• Moho’s discontinuity
• Seismic waves speed up in the denser lithosphere
Slow down in asthenosphere
– Sped up in the solid lower mantle
– Primary waves slowed down and deflected in the liquid
outer core
– Secondary waves is not transmitted through the outer
core (Shadow Zone btw 105 -140 degrees)
–
Tsunami – Large giant Sea Wave cause by an underwater
_____________________________
Measuring earthquakes
1. Seismograph—instrument that records an earthquake’s
vibrations
2. If seismic-wave arrival times are recorded from three
stations, the epicenter can be determined.
3. Richter scale—measures an earthquake’s size, or
magnitude, based on the heights of lines representing the
amount of energy released through seismic waves recorded
on a seismograph (based on a tenfold)
Content Outline
for Teaching
Earthquake Damage
1. Modified Mercalli intensity scale—measures an
earthquake’s intensity based on the amount of structural and
geologic damage
2. Most earthquake damage is caused by surface waves.
3. Tsunamis—when an earthquake occurs on the ocean
floor, the sudden movement pushes against the water and
creates powerful waves that can travel thousands of
kilometers.
Seismic-safe structures are able to stand up against an
earthquake’s vibrations.
1. Many high-rise buildings stand on huge steel and rubber
springs.
2. Underground water and gas pipes are replaced with pipes
that will bend.
3. Highways have cement pillars with spiral reinforcing rods
around them.
F. Predicting Earthquakes
1. Long-range forecasts predict whether an earthquake is
likely to occur in a given area within 30 to 100 years.
Earthquakes and Volcanoes (continued)
15 15
Discussion Question
What can you do to make your home more seismic-safe?
Volcanoes
Volcanoes and Plate tectonics
 Volcano
is a mountain formed when layers of _______ and
volcanic _________ erupt and build up
 Most are ____________
 About __________ are active
What cause Volcanoes
 Magma
is less ____________ then solid rock
 It slowly rises to the earths ___________
 Flows out through an opening called a ___________
 Lava cools quickly and forms _____________ rock
 Opening at the top of the vent is called a ___________
 Pyroclastic flow – massive _____________ of hot glowing
rock and gases (complete destruction)
Where do Volcanoes Form
 1.
Divergent Boundaries
 Mid
__________________
 Forms
long deep cracks called ___________ where magma
flows from
 2. Convergent boundaries
 ________________Mt. Range in Oregon and Washington
 Mt.
Saint ___________
 ____________________
 3. Hot Spots
 ____________________
 Far
from the ____________ of any plate
 Some area of the mantle are ___________ then others
 These hot spots __________ rock which rise to the surface to
form volcanoes
 Once the volcano rises above the water it becomes an
______________
What determines how a volcano Erupts
 _____________of
the magma plays a big role in
determining the manner in how a volcano erupts
 Lave – more ____________ (silicon and oxygen) tend to
be thicker and resists flow
 Lava containing more ___________ and magnesium and
less silica tend to flow easier
 Amount of water __________ in lava influences how lava
erupts
 More water (steam) the more _____________ builds up
and the more violent the eruption is
Forms of Volcanoes
 Three
basic volcanoes
 ____________________
 ____________________
 ____________________
1. Shield
 ___________
eruption
 ____________
volcanoes
 ____________sloping sides
 Ex. Hawaiian, rift zones like Iceland
2. Cinder Cone
 _________________
Volcano
 Throws lava into the air, lava cools and hardens
 Tephra
– small- _________
large – ___________
 Forms
____________ sides
 Sunset crater
3. Composite Volcano
 Can
vary between _____________ or violent
 Alternating layers of __________ and _____________
 Convergent boundaries above ________________ zone
 Mt. St. Helens
 Fissure
Eruption
 Magma
that is highly fluid can ooze from _____________ or
fissures in earths surface