This energy moves in the form of waves. Seismology is the study of these waves generated by earthquakes. In this lesson you will be learning about the four types of seismic waves, how to read a seismogram, and how to find the epicenter of an earthquake. When you pop a balloon, sound waves travel outward in all directions through the air. When rock deep inside the earth suddenly moves, it sends seismic waves outward in all directions through the earth.
Seismic waves start where a large section of rock suddenly shifts.
Pressure waves caused when rock is pushed or pulled forward or backward. Primary waves, the fastest wave sent out by an earthquake, travel down into the earth rather than along the surface. Secondary waves, the second-fastest wave sent out by an earthquake, travel down into the earth rather than along the surface. Surface waves, the slowest earthquake waves, travel along the surface of the earth rather than down into the earth. Although they are the slowest of all earthquake waves, surface waves usually cause more damage to society than P or S waves.