What is an earthquake?• An earthquake is the shaking of the ground

due to the movements of tectonic plates• Earthquakes occur at different plate

boundaries

What happens during an earthquake?

1. Foreshock: any of the usually minor tremors commonly preceding the principal shock of an earthquake

2. Earthquake! 3. Aftershock: smaller earthquakes

which are generated by the continued movement of plates and other materials after the main shock

1. The focus of an earthquake is the point WITHIN the Earth where the earthquake starts. It is the place below the earth’s surface where the rocks tear, come apart, or collide.

Parts of an Earthquake

2. The epicenter is the location on the EARTH’S SURFACE directly above the focus. Surface waves move outward from the epicenter.

3. The fault is the break in thecrust where the earthquake occurs, between two blocks of rock that have moved past each other.

Types of FaultsStrike-Slip, Reverse, NormalEach fault occurs at a different type of boundary!

What is a reverse fault? Convergent Boundary = ReverseOccur at convergent

boundaries, where two plates are colliding

A reverse fault happens when two blocks of crust are pushed up against each other and they slide vertically

These types of earthquakes are usually strong and deep

What is a Normal Fault? Divergent = Normal• Occur at divergent

boundaries, where plates move away from each other

• A normal fault occurs when two blocks of crust are pulled away from each other and slide vertically

• This type of earthquake is usually weak and shallow

What is a strike-slip fault?Transform = Strike-SlipIf two plates have a

transform motion, they will probably have a strike-slip fault between them

A strike-slip fault is when two blocks of crust slide past each other horizontally

These types of earthquakes are moderate and shallow

What Causes Earthquakes?• As tectonic plates push, pull or scrape against each other, stress builds up along faults until the rocks finally move• The elastic rebound theory is the main cause of earthquakes

Elastic Rebound Theory

• Definition: the gradual buildup, and release of stress and strain, between tectonic plates which leads to earthquakes

• http://www.iris.edu/hq/programs/education_and_outreach/animations/4

Just the Basics!

• What do scientists use to measure the strength of an earthquake?

Magnitude

• What do scientists use to measure ground motion?Seismogram

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P WAVES• P waves (primary waves) are compression waves. They push (compress) and pull (expand) in the direction that the wave is traveling. • These move really fast! They arrive first, but cause the least damage.

S WAVESS waves (secondary waves) move in right angles and

are slower than P waves.They arrive second (hence the name), and cause a

moderate amount of damage.

SURFACE WAVES• Travel along the earth’s surface. They do not travel

through the Earth. They move up and down, or side to side. • Although it is the slowest, this is the most

destructive type of wave!