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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