How earthquakes happen

An earthquake of a magnitude of 7.8 rocked Iran and Pakistan on Tuesday. The quake was centered about 50 miles east of Khask, Iran, but was felt as far away as New Dehli, India. More than 35 people were killed in neighboring Pakistan.

Earthquakes are the result of movement between the tectonic plates which move slowly over on the Earth's surface. When plates converge, one will slip under the other. When they collide, earth is pushed upward forming mountains. Diverging plates create spaces from which magma can erupt. When plates lock, energy can build up between them. When they finally give, that energy is released as an earthquake.

Three kinds of waves are emitted during an earthquake. The first are primary waves, also called P-waves, which are felt as a sudden jolt. Those are followed by S-waves, secondary waves, which create a side-to-side movement.

The third kind of wave is surface waves, which radiate out from an earthquake's epicenter. There are two varieties of surface waves. Rayleigh waves cause fierce, rolling vertical movements. Love waves, named after U.K. mathematician A.E.H. love, cause the ground to lash from side to side.