An earthquake generates a series of seismic waves that travel through the interior or near the surface of the Earth. There are four types of seismic waves.
How will three identically engineered buildings react to an earthquake on different types of substrate?
The first set of waves to be detected by seismographs are P waves, or primary waves, as they’re the fastest. They’re compressional or longitudinal waves that push and pull the ground in the direction the wave is traveling. They usually cause very little damage.
S waves, or secondary waves, come next since they travel more slowly than P waves. They travel in the same direction, but they shake the ground back and forth perpendicular to the direction the wave is traveling. S waves are more dangerous than P waves because they have greater amplitude and produce vertical and horizontal motion of the ground surface.
The slowest waves, surface waves, arrive last. They travel only along the surface of the Earth. There are two types of surface waves: Love and Rayleigh waves.
Love waves move back and forth horizontally.
Rayleigh waves cause both vertical and horizontal ground motion. These can be the most destructive waves as they roll along lifting and dropping the ground as they pass.
Want to learn more about earthquakes? Check out this video about how engineers use a giant shaking table to design earthquake safe structures.