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 Tolls YearLocationDeaths 1960Agadir, Moroco Northwestern Iran Northeastern Iran Northern Peru Guatemala Tangshan, China Northeastern Iran China~ (another ~ missing) 2010Haiti~ (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 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