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http:// www.youtube.com/watch?v=JrBaiPN6AW8 Intro. Earthquakes.
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Earthquakes • Most Earthquake waves are caused by movements along faults. The waves originate at the fault several kilometers below the Earth’s surface. Primary and secondary waves travel through Earth’s interior while surface waves travel on the surface. Surface waves are the most destructive. Primary waves arrive before secondary and then finally surface waves.
What are seismic waves • Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs.
Seismic Waves • The two main types of waves are body waves and surface waves. -Body waves can travel through the earth's inner layers-Surface waves can only move along the surface of the planet like ripples on water.
Body Waves • Traveling through the interior of the earth, body waves arrive before the surface waves emitted by an earthquake. • These waves are of a higher frequency than surface waves.
Primary Waves • This is the fastest kind of seismic wave, and, consequently, the first to 'arrive' at a seismic station. • The P wave can move through solid rock and fluids, like water or the liquid layers of the earth. It pushes and pulls the rock it moves through just like sound waves push and pull the air.
Primary Waves • Have you ever heard a big clap of thunder and heard the windows rattle at the same time? The windows rattle because the sound waves were pushing and pulling on the window glass much like P waves push and pull on rock.
Primary Waves • Sometimes animals can hear the P waves of an earthquake. Dogs, for instance, commonly begin barking hysterically just before an earthquake 'hits' (or more specifically, before the surface waves arrive). Usually people can only feel the bump and rattle of these waves.
Primary Waves • P waves are also known as compressional waves, because of the pushing and pulling they do. Subjected to a P wave, particles move in the same direction that the the wave is moving in, which is the direction that the energy is traveling in • http://www.geo.mtu.edu/UPSeis/images/P-wave_animation.gif
http://www.youtube.com/watch?v=-zNyVPsj8zc • http://www.youtube.com/watch?v=yOGoKCK17a4 • waves
Secondary Waves • The second type of body wave is the S wave or secondary wave, which is the second wave you feel in an earthquake. • An S wave is slower than a P wave and can only move through solid rock, not through any liquid medium. • S waves move rock particles up and down, or side-to-side--perpindicular to the direction that the wave is traveling in. ((What kind of wave is this?))
Secondary Waves • http://www.geo.mtu.edu/UPSeis/images/S-wave_animation.gif
Surface Waves • Travelling only through the crust • surface waves are of a lower frequency than body waves • Easily distinguished on a seismogram • Surface waves are almost entirely responsible for the damage and destruction associated with earthquakes.
Recap • P waves, or primary waves, are compressionalwaves that are longitudinal in nature, or vibrate in the same direction in which they travel. P waves travel faster than the speed of sound and can travel through any material. • S waves, or secondary waves, are shear waves that are transverse in nature, the vibration being perpendicular to the direction of travel, and can travel only through solids.
Recap • http://www.youtube.com/watch?v=8hrSH8WtDV8
Seismic Waves and Disaster • Due to the seismic waves they generate, earthquakes can cause massive disaster to the Earth's crust. • The strength of the waves can cause problems including but not limited to:-ground motion -ground sliding -instability of the soil -ground failure • Seismic waves produced by an earthquake under the ocean can translate into a tsunami.
Seismographs • A seismograph is an instrument that is used to detect seismic waves. The instrument consists of: a seismometer (the actual measuring device), an amplifier and a display unit. • The seismograph measures movement in just one direction. Therefore, many stations' placements include more than one seismograph to track all directions. • The measurements allow scientists to accurately determine the location, the type, the distance and the magnitude of the earthquake.
Epicenter • point on the Earth’s surface that is directly above the focus, the point where an earthquake or underground explosion originates
Mexico City Earthquake • Mexico City is vulnerable even to distant earthquakes because much of it sits atop the muddy sediments of drained lake beds that quiver as quake waves hit. • The magnitude-8.1 quake in 1985 that killed at least 6,000 people and destroyed many buildings in Mexico City was centered 250 miles (400 kilometers) away on the Pacific Coast.
http://www.youtube.com/watch?v=mNWCYG2MnC8 • http://www.youtube.com/watch?v=vjN2eR8QzDw • Documentary
