Master the Science of Earthquakes

Seismic activity refers to the frequency, size, and type of earthquakes an area experiences over time.

Earthquakes are caused by the movement and interaction of tectonic plates.

A seismograph is an instrument used to measure and record ground-shaking activity caused by earthquakes.

A seismogram is the recording made by a seismograph, which shows the ground-shaking activity caused by an earthquake.

Seismic activity cannot be measured directly at the location of an earthquake because it occurs deep underground.

When tectonic plates bump into each other, the edges get stuck while the rest of the plate continues to move, eventually causing the rock in the location where the plates are stuck to break and release a large amount of built-up energy, resulting in an earthquake.

The two types of body waves produced by an earthquake are P waves and S waves.

P waves travel through the ground in a compressional wave fashion, where the wave compresses the medium it's traveling through as it moves along.

S waves move through the ground in an up and down wave movement, similar to a wave over the surface of water. This is called a transverse wave.

The two types of surface waves produced by an earthquake are Love waves and Rayleigh waves.

Love waves move across the ground in a snake-like fashion, moving from side to side. They are a transverse wave flipped on its side, moving the ground horizontally.

Rayleigh waves cause the most damage during an earthquake, as they roll across the surface of the earth similar to an S wave underground or a wave rolling across the surface of the ocean.

Seismic activity is the frequency, size, and type of earthquakes an area experiences over time.

A seismogram is the recording made by a seismograph, which measures the ground shaking produced by an earthquake.

Earthquakes are measured using a seismograph to record the ground shaking. The size and length of the lines on the seismogram relate to the magnitude, or strength, of the earthquake.

Body waves are seismic waves that travel through the earth's inner layers. They include primary waves (P waves) and secondary waves (S waves).

Primary waves travel the fastest and are the first waves to register on a seismograph. They travel by compressing the ground, similar to how a Slinky gets compressed if you shimmy it back and forth.

Secondary waves are transverse waves that travel up and down like a Slinky would if you whipped it vertically. They are the second waves to reach a seismograph.

Surface waves are seismic waves that travel across the earth's surface. They cause the most damage during an earthquake.

Love waves are the fastest surface waves and move horizontally across the ground. Rayleigh waves are slower but often larger, rolling up and down like S waves on the surface.