Forces in Earth’s Crust

Chapter 6 Section 1

Earthquakes

• Elasticity is the ability for an object to return to or keep its original shape

Which is more elastic…

a bouncy ball or a bowling ball?

Earthquakes

• Elastic limit – the most that something can be stretched or bent before breaking

Earthquakes

• Tectonic movements supply the force that bend and stretch rocks

• When the elastic limit of rock is passed, it breaks and produces forces called earthquakes.

• 80% of all earthquakes occur along edges of the Pacific Plate (Ring of Fire)

Faults

• the place where rocks break and move by one another

• There are 3 types of faults

Normal Faults

• Caused by tension forces

• Example: Sierra Nevadas

Normal Faults

Hangin

g W

all

Reverse Faults

• Caused by compression forces

• Example: Himalayas

Reverse Faults

Hanging wall

Strike-Slip Fault

• Caused by shearing forces

• Occurs at transform boundaries

• Irregular surfaces snag each other

• Example: San Andreas Fault

Strike-Slip Fault

Let’s Review

• What are the 3 kinds of faults?– Tension– Compression– Shearing

• What are the 3 kinds of forces that cause faults?• At what boundaries do they form?

– Normal– Reverse– Strike-slip

Divergent

Convergent

Transform

Earthquakes can be dramatic

or almost unnoticed

Changing Earth’s Surface

• Sometimes plate movements cause the crust to fold (mountain building)

Changing Earth’s Surface

• Stretching can cause fault-block mountains

Changing Earth’s Surface

• Large, flat, blocks of rock can be pushed upward – high above sea-level (plateau)