o What is an Earthquake Earthquakes Earthquakes Vibrations

o What is an Earthquake? Earthquakes: Earthquakes Vibrations (seismic waves) within Earth materials -produced by the rapid release of energy ü Earth’s crust is in constant motion due to tectonic forces ü Earth’s crust can store elastic energy ü When forces exceed the elastic limits and structural strength of the rocks, the rocks will break and/or move producing vibrations that travel outward in all directions

Earthquakes o The actual place underground where the rocks break producing vibrations is called the focus o The place on the surface directly above the focus is called the epicenter

What types of forces are created? Tension Force: Force ü stretching or pulling force ü Makes a normal fault

http: //www. geo. uib. no/jordskjelv/index. php? topic=earthquakes&lang=en

What types of forces are created? Compression Force: Force ü force pushing something together ü Makes a reverse fault

http: //www. geo. uib. no/jordskjelv/index. php? topic=earthquakes&lang=en

What types of forces are created? Shear Force: Force ü a system of forces that operates against a body from different sides ü Makes a strike-slip fault

http: //www. geo. uib. no/jordskjelv/index. php? topic=earthquakes&lang=en

What causes Earthquakes? ü Movement along faults: energy exceeds the friction holding the sides together and is suddenly released ü Movement of magma (volcanic) ü Volcanic eruptions

Seismic Waves

3 Types of seismic Waves ü § § P waves (primary waves) Compressional wave Particles move back and forth in the same direction as the wave Travels the fastest Can pass through solids and liquids (gases also) Does not cause damage

Types of Waves ü S wave (secondary wave, shear wave) § § Particles move at right angles to the direction of the wave Travels slower than P waves Can pass through solids only Does not cause damage

Types of Waves ü Surface wave § § Particles move in elliptical orbit Originates on the surface after the P and S waves go straight up from the focus and reach the surface The L wave causes the damage and will be the strongest at the epicenter Travels the slowest

How do we Measure Earthquakes? Earthquake are recorded by a seismograph

How do we Measure Earthquakes? ü Intensity – a measure of the effects on an earthquake at a particular location ü Magnitude: Magnitude a measure of the strength or amount of energy released during an earthquake

How do we Measure Earthquakes? ü Richter Scale: Scale Measures the amplitude of earthquake waves on seismograms § Scale from 1 -10 § Each number is 10 times the amplitude of the number below

Earthquake Dangers o Most injuries and deaths are caused by falling objects and most property damage results from fires that start ü Tsunami: Tsunami seismic sea wave sometimes generated when an earthquake originates on the ocean floor

Tsunami—December 2004 http: //www. bedford. k 12. ny. us: 16080/flhs/science/images/tsunami 2004/

Earthquake Dangers ü Landslides