Earthquakes

Earthquakes

• An earthquake is a shaking of Earth’s crust caused by a release of energy.

• Earthquakes are often more destructive than volcanoes because the area affected can be greater.

Earthquakes• More than 1 million earthquakes occur

each year – that’s about 1 every 30 seconds.

Death TollsYear Location Deaths

1960 Agadir, Moroco 12 000

1962 Northwestern Iran 12 230

1968 Northeastern Iran 12 000

1970 Northern Peru 66 974

1976 Guatemala 22 778

1976 Tangshan, China 800 000

1978 Northeastern Iran 25 000

2008 China ~70 000 (another ~18 000 missing)

2010 Haiti ~50 000 (est.)

Causes of Earthquakes

• The major cause of earthquakes is when stress builds up within Earth’s crust.

• This stress occurs when plates move past each other.

Normal Faults

Reverse Faults

Strike-slip Faults

How Deep?

• Most earthquakes occur between 30-700 km below the surface.

• The type of plate boundary involved will determine the depth of the earthquake.

How Deep?

• Focus: The place inside the Earth where the earthquake actually occurs.

• Epicenter: The point on Earth’s surface directly above the focus.

Earthquake Waves

1. Body Waves:• Primary or P-waves • Secondary or S-waves

2. Surface Waves:• L-waves

Body Waves

• Travel through the body of the Earth.

• P-waves:–Move back and forth (compression).–Can travel through any material.

• Solid rock, magma, water, air.

Body Waves

• S-waves:–Move up and down.–Are almost twice as slow as P-waves.–Cannot travel through liquids.

Surface Waves

• When P and S waves reach the surface, they create an L-wave.

• They resemble ripples on a pond and can travel about 3 km/h.

Surface Waves

Seismographs

• The instrument used to record earthquake waves is called a seismograph.

• A seismogram is the data recorded from the seismograph.

Measuring an Earthquake

Earthquake Magnitude

• The scale used for earthquake magnitude is the Richter Scale.

• The Richter Scale measures the amount of energy released by an earthquake.

Magnitude 6.0