What is a Seismic Wave?

A seismic wave is a type of shockwave that vibrates through or under the surface of the Earth. These waves can be caused by a variety of things, including sudden explosions under the Earth's surface, wind, or strong and repetitive ocean waves. The damage caused by seismic waves can be severe.

The area of study concerned with monitoring and analyzing earthquakes and seismic waves is called seismology; an expert in seismology is a seismologist. These scientists interpret the geological composition and structures of the Earth. Seismologists can also evaluate the potential dangers from seismic waves and research ways to minimize their impact. Typically, seismologists categorize seismic waves into one of two types, body waves or surface waves.

Body waves flow through the inner parts of the Earth and can bend and retract depending on the substance through which they pass. A primary wave, or P-wave, is a type of body seismic wave that travels at great velocity beneath the surface and is usually recorded first at the site of an earthquake. It can move through solids and liquids by compressing and expanding the material in its way.

A secondary wave, or S-wave, is another type of body wave. This is a slower, seismic wave that travels by pushing rock particles perpendicular to its path. An S-wave, however, can not pass by gas and fluids, and travels only through solids. Since the outer layer of the Earth’s core is made out of liquid molten lava, the waves need to bend and go around it to get to the site of the earthquake. Seismologists timed and used this property of secondary waves to prove the existence of the core itself.

In addition to body waves, there are surface waves. Surface waves are generally responsible for the largest amount of destruction associated with earthquakes. This type of seismic wave moves only through the Earth's crust and is similar to a water wave. Often, it is generated when the source of the earthquake is close to the surface. It can shake the foundations of buildings and bring very heavy structures down. Surface waves are also divided into two subtypes: Rayleigh waves, which travel as ripples and can be spotted by the human eye, and Love waves, which split the ground horizontally.

Seismologists attempt to determine the distance and source of an earthquake by measuring the difference in arrival times between primary and secondary waves. The measurements are typically made by a device called a seismograph. The findings are often stored into a computer and can be used to predict future events and possible damage inside the active region.