Earthquakes Video: http://www.youtube.com/watch?v=VSgB1IWr6O4

What is an Earthquake? Earthquakes: Vibrations (seismic waves) within Earth materials are produced by the rapid release of energy Earth’s crust is in constant motion because of tectonic forces Earth’s crust can store elastic energy 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 The actual place underground where the rocks break producing vibrations is called the focus. The place on the surface directly above the focus is called the epicenter.

Animation: http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::640::480::/sites/dl/free/0072402466/30425/16_04.swf::Fig.%20%2016.4%20-%20Focus%20of%20an%20Earthquake

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

Worldwide 'Quakes http://earthquake.usgs.gov/earthquakes/map/

Recent 'Quakes http://earthquake.usgs.gov/earthquakes/map/

Ohio’s Fault Lines

Fault lines & Earthquakes

Seismic Waves Seismic waves are vibrations that travel through the earth carrying energy released during an earthquake. They carry the energy of an earthquake away from the focus outward in all directions. Three kinds of seismic waves: P waves S waves surface waves

Seismic Waves

3 Types of seismic Waves P waves (primary waves) ComPressional wave particles vibrating Parallel to the direction the wave travel (they are longitudinal Push Pull waves) Travel through solids, liquids & gases - all Physical matter Travels the fastest - Phastest (sorry! - sad I know, but if if helps you remember...) Does not cause damage

P Waves -- Primary Waves Compression or longitudinal Waves The medium is vibrating and particles are compressed and decompressed. Seismic waves can be longitudinal. These are called P-waves. They travel faster than S-waves and arrive first at distant seismic stations. P-waves can travel through solids liquids or gasses.

Another view of the particles vibrating back and forth This is what is happening to the earth when a P wave travels through – the molecules that make up the earth vibrate as energy travels through.

Types of Waves S wave (secondary wave, Shear wave) Waves move at up and down. (right angles) Can pass through solids only (Solely Solids) Travels slower than P waves. Part of the “body wave” that will eventually cause damage.

Secondary Wave (S Wave) The energy moves through the medium, but the medium moves back and forth perpendicular to the wave energy

Even though this picture shows a sound wave, the fact that the waves spreads out in all directions is the important thing.

Types of Waves L wave (long wave; also called surface wave) Move up and down & side to side Travels through only solids SLOWEST Wave MOST DANGEROUS

Surface Wave in an Earthquake How would this feel if you were in an earthquake? If you watched a surface wave move through a very large parking lot, what would it look like?

How do we Measure Earthquakes? Earthquake waves are recorded by a seismograph and the recording of waves on paper is called seismogram

How do we Measure Earthquakes? Magnitude: a measure of the strength or amount of energy released during an earthquake Richter Scale: Measures the amplitude of earthquake waves on seismograms Scale from 1-10

Earthquake Dangers Most injuries and deaths are caused by falling objects and most property damage results from fires that start Ocean waves caused by earthquakes are called seismic sea waves, or tsunamis. http://video.nationalgeographic.com/video/news/japan-tsunami-2011-vin

Tsunami—December 2004 http://www.bedford.k12.ny.us:16080/flhs/science/images/tsunami2004/