Seismology
There are two main types of seismic waves: body waves and surface waves.
Body waves can be split up further into two different types of waves: primary or P waves and secondary or S waves. These two types of waves are distinguished by the way they travel and what materials they travel through. P waves compress and stretch rocks in the direction the wave is traveling. Solids, liquids, and gasses can resist the stresses that come along with being compressed and stretched that change volume and bounce back once the stress is gone. This is why P waves can travel through all three of these materials. S waves shake the particles at a right angle to the direction of travel. While P waves temporarily change the volume of the material it's traveling through, S waves change the shape of the material it's traveling through. Gases and liquids won't return to their original shape once stress is removed, so S waves cannot travel through these materials.
There are also two types of surface waves. They don't have different names. One type causes Earth's surface to move like ocean waves and the other type cause Earth's materials to move side to side. Surface waves cause the most damage.
Body waves can be split up further into two different types of waves: primary or P waves and secondary or S waves. These two types of waves are distinguished by the way they travel and what materials they travel through. P waves compress and stretch rocks in the direction the wave is traveling. Solids, liquids, and gasses can resist the stresses that come along with being compressed and stretched that change volume and bounce back once the stress is gone. This is why P waves can travel through all three of these materials. S waves shake the particles at a right angle to the direction of travel. While P waves temporarily change the volume of the material it's traveling through, S waves change the shape of the material it's traveling through. Gases and liquids won't return to their original shape once stress is removed, so S waves cannot travel through these materials.
There are also two types of surface waves. They don't have different names. One type causes Earth's surface to move like ocean waves and the other type cause Earth's materials to move side to side. Surface waves cause the most damage.
A seismograph is the instrument used to record earthquakes. It works by having a weight freely suspended from a support that is attached to bedrock. When an earthquake hits, the instrument stays still and stationary moves, recording the waves of the earthquake.
Source: http://earthquake.usgs.gov/learn/glossary/?termID=167