Chapter 14
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
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