KEY TERMS:
Earthquake: A natural disaster that results from the movement of the Earth's tectonic plates.
Seismic Waves: The waves of energy caused by the sudden breaking of rock within the Earth. They are the energy that travel through the Earth and are recorded by seismographs.
Seismographs: An instrument that measures the intensity, direction and duration of seismic waves.
Seismology: The study of earthquakes and seismic waves that move through and around the Earth.
Seismologist: The scientists that studies earthquakes and seismic waves.
FACTS ABOUT SEISMIC WAVES:
Thanks to the recordings of earthquakes and seismic waves, scientists were eventually able to discover the Earth's core and other layers and make an approximate map of what these are like. These waves are able to change speed, bend or reflect off of different materials and layers below the Earth.
Earthquakes are often the cause of Tsunamies and Volcanic eruptions, which often form along the fault line where one tectonic plate meets another. A common area for volcanic eruptions is along the "Ring of Fire", along the ridge where Australia's tectonic plate meets the one under the Pacific Ocean. This area is said to produce over 80% of the World's annual Earthquakes.
High temperature tends to lower the speed of seismic waves, whereas pressure increases it. The pressure increases with depth because of the weight of the rocks pressing inwards.
Meteor impacts and volcanic eruptions can also cause seismic waves in the Earth's surface, which might cause Earthquakes depending on the size of these.
An Earthquake is generally measured using the Richter Scale which expresses the Earthquake's magnitude as a decimal or wholenumber. Earthquakes with magnitude of about 2.0 or less are usually called microearthquakes and we often don't feel them at all, but find out about them using seismographs. Quakes with magnitudes of 4.5 or greater are strong enough to be felt, and are pretty common around the world, occuring several thousand times a year. The earthquakes you see on the news, however, have magnitudes of 8.0 or higher and have the potential to be very destructive.
The most powerful earthquake ever recorded on Earth was in Valdivia, Chile. Occurring in 1960, this Earthquake had a magnitude of 9.5 on the Richter Scale.
The word "Seismic" comes from the Greek word "seismos" which literally means "Earthquake".
WHAT TYPES OF WAVES ARE THERE?
There are 3 types of Seismic waves:
P WAVES: Also known as primary or pressure waves, these waves travel at the fastest speeds, moving rock and dirt particles back and forth as they move through the ground. They can easily pass through solids, liquids and gases and often arrive at the surface of the Earth with an abrupt "thud".
S WAVES: also known as secondary waves, they are slower than P waves and can only travel through solid rock and not through any liquid medium. They move the Earth up and down.
SURFACE WAVES: They travel just under the Earths surface and although they are much slower than S waves they have a larger amplitude and can be the most destructive. These types of waves can be divided into two categories:
RAYLEIGH WAVES: also called ground roll, they travel in ripples which are similar to to those on the surface of water. They can be easily spotted in open spaces such as parking lots or meadows.
LOVE WAVES: these are the fastest type of surface wave and are capable of moving the Earth from side to side.
GRAPHS OF THE WAVES:
look down
FORMULAS FOR THE SEISMIC WAVES:
look down
BIBLIOGRAPHY:
http://earthquake.usgs.gov/learn/topics/measure.php
http://www.sciencekids.co.nz/sciencefacts/earth/earthquakes.html
https://www.dosomething.org/facts/11-facts-about-earthquakes
http://sciencelearn.org.nz/Contexts/Earthquakes/Science-Ideas-and-Concepts/Seismic-waves
http://science.howstuffworks.com/nature/natural-disasters/earthquake4.htm
http://www.geo.mtu.edu/UPSeis/waves.html
http://www.thefreedictionary.com/seismograph
http://sciencelearn.org.nz/Contexts/Earthquakes/Science-Ideas-and-Concepts/Seismic-waves
http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/waves_and_interior.html