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What is Seismology?
What are Seismic Waves?: Types of Seismic waves
Where do Earthquakes Happen?
Why do Earthquakes Happen?
How is the Epicenter of an Earthquake Located?
How are Earthquakes Magnitude Measured?

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Seismology is the study of earthquakes and seismic waves that move through and around the earth.
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A seismologist is a scientist who studies earthquakes and seismic waves.

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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.
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There are two types: P wave and S wave.

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The first kind of body wave is the P wave or primary wave .
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.

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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.

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Earthquakes occur all the time all over the world, both along plate edges and along faults.
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Along Plate Edges : Most earthquakes occur along the edge of the oceanic and continental plates .
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Along Faults : Earthquakes can also occur far from the edges of plates, along faults.

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Earthquakes are usually caused when rock underground suddenly breaks along a fault.

• A single seismogram can tell a seismologist how far away the earthquake was but it does not provide the seismologist with enough information to locate the exact epicenter. For that, the seismologist needs at least three seismograms.
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Determining distance to an earthquake epicenter depends on the fact that different seismic waves travel at different speeds. P-waves always arrive at a seismometer first, but the amount of time it takes for the S-waves to arrive after the P-wave indicates distance to the epicenter.

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The most widely used method the Richter scale , was developed by Charles
F. Richter in 1934. It used a formula based on amplitude of the largest wave recorded on a specific type of seismometer and the distance between the earthquake and the seismometer.
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Magnitudes are based on a logarithmic scale (base 10). What this means is that for each whole number you go up on the magnitude scale, the amplitude of the ground motion recorded by a seismograph goes up ten times.

• http://www.geo.mtu.edu/UPSeis/intensity.html
• http://www.earthquakescanada.nrcan.gc.ca/infogen/seismolog-eng.php
• http://en.wikibooks.org/wiki/High_School_Earth_Science/Me asuring_and_Predicting_Earthquakes