4.7 Earthquakes Lesson

4.7 Earthquakes

​How and why do plates move?

​

Plate Tectonics

An Introduction

There was once a time when you could take a stroll from North or South America to Africa no problem!

Plate tectonics theorizes that Earth's outer layer is made up of large, moving pieces called plates! These plates are in constant motion.

Multiple Choice

About how fast do you think the tectonic plates move?

• As fast as students leave school at the end of the day

• As fast as your nails grow

• As fast as you can run

Tectonic plates move about as fast as your fingernails grow -

That's 2 to 15 centimeters
a year!

These plates move due to heat from Earth's core.

• Heat rises at spreading centers, pushing plates apart

• This process resulted in the breakup of Pangea, the formation of the Atlantic Ocean, and how Earth's surface appears today!

Multiple Choice

What do you think happens when two plates converge (collide)?

• Mountains form

• A trench forms

• They change course and move somewhere else

Through collisions, plates can raise incredible mountain ranges!

The Himalayan mountains formed as the Indian plate crashed into the Eurasian plate.

Earth's Layers

• Earth is a sphere with 4 different layers.

• These layers are: Crust, Mantle, Outer Core, & Inner Core.

Earth's Crust

• The crust is its rocky outer layer.

• It is hard and made of many minerals.

• The crust is the thinnest in the ocean and thickest under mountains.

• This layer moves around on plates.

• This layer can be 3 to 43 miles thick.

Earth's Tectonic Plates

• The Earth's crust is broken into plates.

• These plates are able to move due to the warm mantle under them.

• The interaction between plates is what creates the landforms on the Earth's surface.

Earth's Mantle

• This is the thickest layer, making up 2/3 of the Earth's mass.

• The mantle has some liquid rock but is mostly solid.

• High temperatures and pressure cause it to move like warm plastic.

• It is approximately 1,790 miles thick.

Earth's Core

• At the center of the Earth, there is the core.

• It is mostly made of metal.

• It has two parts: Outer and Inner.

• This layer is very hot.

Earth's Outer Core

• The outer core is molten, liquid metal.

• It is extremely hot and is able to move.

• The outer core is approximately 1,410 miles thick.

Earth's Inner Core

• The inner core is made of solid metal- iron and nickel.

• These metals are the reason the Earth has a magnetic field.

• The inner core is approximately 750 miles thick.

Multiple Choice

What layer is shown by letter D?

• Crust
• Mantle
• Outer core
• Inner core

Multiple Choice

What layer is shown by letter C?

• Crust
• Mantle
• Outer core
• Inner core

Multiple Choice

What layer is shown by letter B?

• Crust
• Mantle
• Outer core
• Inner core

Multiple Choice

What layer is shown by letter A?

• Crust
• Mantle
• Outer core
• Inner core

Multiple Choice

What do scientists call the boundary between two tectonic plates?

• Vaults

• Crusts

• Faults

• Mantles

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The Ring of Fire

Multiple Choice

The Ring of Fire is a large area around the ________ Ocean.

• Arctic

• Atlantic

• Indian

• Pacific

Plate tectonics:

• The Earth’s surface is a little bit like a jigsaw.

• There are 7 major tectonic plates.

• Most of these are where
  different continents are.

• A plate usually moves
  between 1 and 6 inches per year.

The 3 types of plates

• ​Transform Boundaries (Moving Plate)

  Two plates usually slide past each other, causing fault lines between plates. Usually, earthquakes occur.

• Convergent Boundaries (Continental Plate)

  Two plates pull together, causing one to move under the other in a process called subduction

• Divergent Boundaries (Oceanic Plate)

  This is when 2 plate boundaries push apart and form a ‘rift’.

The crust is the ocean floor.

If you stand at the bottom of the ocean, you are standing on Earth's crust.

The crust is thin at the ocean floor.

* The crust is found under the ocean but is thin.

*It is about 3 miles from the top to the bottom of the ocean.

What can be found at the bottom of the ocean floor?

*The longest chain of mountains in the world is called the mid ocean ridge.

*The mid ocean ridge is found at the bottom of the ocean.

Multiple Choice

Where is the longest chain of mountains in the world found?

• North America

• South America

• ocean floor

What is seafloor spreading?

• Seafloor spreading is when the magma rises to the ocean floor.

• Seafloor spreading begins at the midocean ridge.

• When the magma comes in contact with the ocean floor, it cools down and becomes a rock called basalt.

faults

breaks or cracks where plates come together

seismologist

a science that deals with earthquakes and with artificially produced vibrations of the earth

Earthquakes

• Movements in Earth's crust caused by a sudden shift of Earth's plates

• Earth's plate movement puts stress on rock, and earthquakes occur when the crust shakes by the release of the accumulated energy.

amplitude

a measure that relates to the amount of energy of a wave

How Big or small an earthquake is!

magnitude

the amount of energy released by an earthquake

seismic wave

a vibration caused by an earthquake

transverse wave

a wave that vibrates perpendicular to the direction that the energy moves

wavelength

the distance between wave crests or troughs

Record and measure earthquakes

• Seismograph: mesuring seismic waves

• Richter scale: measuring magnitude (the largest movement)

• Mercalli scale: measuring what people felt and what happened during an earthquake (I to XII)

This is a seismograph for measuring how strong an earthquake is!

​When earthquakes occur under the sea, they can cause a tsunami!
A very large wave of water!

Mercalli scale

Multiple Choice

_____ move material back and forth.

• Transverse waves

• Longitudinal waves

• Wavelengths

• None of the above

Multiple Choice

Which earthquake releases more energy?

• an earthquake of 6.0

• an earthquake of 7.0

• an earthquake of 5.0

What to do in an earthquake!

Safe Structures

• Reinforced concrete, metal, and wood

• short or tall buildings

• Bridges: motion dampeners, rubber joints

Buildings need to resist LATERAL FORCES in earthquakes

• bracing

• shear wall

• damper

damper