Understanding the concept of Seismic waves
Seismic waves are those energy waves which travels through or within the earth and are often caused by a tectonic activity such as an earthquake, volcanic eruptions, magma movement, landslide etc. The propagation velocity of the waves depends on the density and elasticity of the medium in which it travels.
Two main parts of Seismic Waves
Seismic waves are of several different kinds and types, as they all move in different ways and directions. The two main categories in which seismic ways can be divided are Body waves and Surface waves. Further Body waves are divided into two types– Primary Waves and Secondary waves. And Surface Wave intoLove Waves.
Body waves travel through the interior of the Earth along paths controlled by the material properties in terms of density and modulus (stiffness) which in turn, vary according to temperature, composition, and material phase.
Primary Waves (P Waves) – They are the fastest moving waves traveling at the speed 1 to 5 miles per second (1.6- 8km/sec).They are compressional waves that are longitudinal in nature They can pass through solids, liquids, and gases easily. As they travel through Rocks, the waves move tiny rock particles back and forth- pushing them apart and then back together in line with the direction the wave is traveling. These waves typically arrive at the surface as an abrupt thud. In the air, they take the form of sound waves, hence they travel at the speed of sound.
Secondary Waves(S Waves) – They move a little more slowly than P waves and can only pass through Solids. S-waves are shear waves that are transverse in nature. As S Waves move they displace rock particles outward pushing them perpendicular to the path of waves. This results in the first period of rolling associated with earthquakes. Unlike p waves, S waves don’t move straight through the earth. They are stopped at the liquid layer in Earth’s core. They are also known as Shear Waves.
Love Waves (L waves) – They move along the surface of the earth and hence also known as surface waves. They are to blame for most of an earthquake’s carnage. They move up and down the surface of the earth rocking the foundations of man-made structures. L waves are slowest of all waves means they arrive the last. So the most intense shaking usually comes at the end. Love waves produce entirely horizontal motion. Love waves are dispersive, that is, the wave velocity is dependent on frequency, with low frequencies normally propagating at the higher velocity