 Seismic waves are generated by earthquakes. For example, two tectonic blocks suddenly slip. There is energy that's generated by that earthquake and that it moves through the earth in the form of seismic waves. We record the ground motion by sensitive instruments called seismographs. Some researchers use seismic waves as a tool to basically study the interior of the earth in the same way that the medical doctors use x-rays to look at the interior of the patient's body. Apart from seismologists who use seismic waves that penetrate deep in the earth's interior, there are also mineral physicists who use experimental setting to look at the behavior of rocks at high pressures and high temperatures.