6. What are seismic waves?

Seismic waves are the vibrations or waves of energy that travel through the Earth's interior and along its surface as a result of an earthquake, explosion, or other seismic event. These waves carry the energy released by the seismic source and are responsible for the shaking and ground motion observed during earthquakes. Seismic waves can be classified into several types based on their motion, speed, and propagation characteristics. The three main types of seismic waves are:

1. Primary Waves (P-Waves):

   • Primary waves are the fastest seismic waves and are the first to arrive at seismograph stations following an earthquake.
   • They are compressional waves that travel by alternately compressing and expanding the material through which they pass.
   • P-waves can travel through solids, liquids, and gases and are capable of passing through the Earth's interior (mantle and core).
   • They cause particles of the material to vibrate in the direction of wave propagation, similar to the way sound waves travel through air.

2. Secondary Waves (S-Waves):

   • Secondary waves arrive at seismograph stations after P-waves and are slower than P-waves.
   • They are shear waves that propagate by causing particles of the material to move perpendicular to the direction of wave propagation.
   • S-waves can only travel through solids and are unable to pass through liquids or gases. This property is used to infer the presence of a liquid outer core beneath the Earth's mantle.
   • S-waves cause the ground to move from side to side or up and down as they pass through the Earth's interior.

3. Surface Waves:

   • Surface waves travel along the Earth's surface and are responsible for much of the shaking and damage observed during earthquakes.
   • They are slower than both P-waves and S-waves and typically arrive at seismograph stations last.
   • Surface waves have two main types: Love waves and Rayleigh waves.
   • Love waves cause horizontal shearing motion in the ground, while Rayleigh waves cause both vertical and horizontal motion, similar to the motion of ocean waves.
   • Surface waves can produce the most significant ground shaking and are responsible for the majority of the damage caused by earthquakes to buildings and infrastructure.

Seismic waves are detected and recorded by instruments called seismographs or seismometers, which measure the motion of the ground caused by the passing waves. Analysis of seismic waves recorded by seismographs provides valuable information about the location, magnitude, depth, and focal mechanism of earthquakes, as well as the Earth's internal structure and composition.