Earthquakes

Pages B104-B127

Faults are classified by how rocks move.

• The blocks of rock along different types of faults move in different directions, depending on the kinds of stress they are under.

• There are three types of faults:– Normal Faults– Reverse Faults– Strike-Slip Faults

Normal Faults

– Movement of the plates causes tension– Rocks above the fault surface move downward in

relation to the rocks below the fault surface– Common near boundaries where tectonic plates

are moving apart– Great Rift Valley of Africa.

Normal Fault

Reverse Faults

– Compression forces are applied because Earth’s plates are coming together

– Causes rocks to bend and break– Rocks above the fault surface are forced up and

over the rocks below the fault surface– The Himalayas Mountains have many earthquakes

along reverse faults

Reverse Faults

Strike-Slip Faults

– Earth’s plates move sideways to one another– Creates a shear force– Rocks on either side of the fault surface are

moving past each other without much upward or downward movement

– San Andreas Faults is a strike-slip fault

Strike-Slip Fault

Seismic Waves– Primary waves• Energy waves that cause rocks to move back and

forth in the same direction• Compression and stretching forces are created

– Secondary waves• Energy waves that cause rocks to move at right

angles to the wave– Surface waves• Energy waves that reach the Earth’s surface• Energy waves that move rocks in an elliptical

motion

Locating an Epicenter

• Seismic waves do not travel through earth’s surface at the same speed– Primary waves are the fastest– Surface waves are the slowest

• Seismograph stations– Record the information from the earthquake by

recording the different types of waves as they reach the station

Using Seismic Waves to Map Earth’s Interior

• Structure of Earth– Inner core• Solid and very dense• Composed of mostly nickel and iron

– Outer core• Liquid layer that surrounds the inner core• Composed of nickel and iron

Using Seismic Waves to Map Earth’s Interior

– Mantle• Largest layer located above the inner core• Composed of silicon, oxygen, magnesium, and

iron– Crust• Outermost layer• Solid and similar in composition to the mantle

Seismograph

• Seismograph is an instrument that constantly records ground movements.

• The recording of an earthquake looks like a group of wiggles in a line. The height of the wiggles indicates the amount of ground movement.

• If it measures from side to side it has a heavy weight hanging from the wire.

• If it measures from up and down movements it has a heavy weight hanging from a spring