Seismic waves are waves of energy that travel through the Earth's interior as a result of earthquakes, volcanic activity, or other sources of energy release. They carry the energy from the source and cause the ground to shake, resulting in seismic vibrations that can be detected and studied.
There are three main types of seismic waves:
Primary waves (P-waves): P-waves are also known as compressional waves or longitudinal waves. They are the fastest seismic waves and can travel through solids, liquids, and gases. P-waves cause particles in the material to vibrate in the same direction as the wave's propagation. On a seismograph graph, P-waves appear as the first and fastest upward deflection.
Secondary waves (S-waves): S-waves are also called shear waves or transverse waves. They are slower than P-waves and can only travel through solids. S-waves cause particles to move perpendicular to the direction of wave propagation. On a seismograph graph, S-waves appear as the second set of deflections after the P-waves.
Surface waves: Surface waves are seismic waves that travel along the Earth's surface. They are slower than both P-waves and S-waves but have larger amplitudes, which can cause significant damage. There are two types of surface waves: Love waves and Rayleigh waves. Love waves move in a horizontal, side-to-side motion, while Rayleigh waves have both vertical and horizontal motion. On a seismograph graph, surface waves appear as slower, rolling waves with larger amplitudes.
In the field, seismic waves can be distinguished by their arrival times and motion. P-waves are the first to arrive at a seismograph station because they travel fastest. S-waves arrive second, and surface waves arrive last. By measuring the time interval between the arrivals of different waves, scientists can calculate the distance from the seismic source.
In terms of motion, P-waves cause a back-and-forth motion parallel to the wave's direction, while S-waves cause a shaking motion perpendicular to the wave's direction. Surface waves cause rolling or swaying motion on the ground surface. By observing and analyzing the ground motion during an earthquake or using specialized equipment, seismologists can identify the different types of seismic waves and their characteristics in the field.