Hint: During an earthquake, surface waves are the seismic waves that cause the most damage. Unlike other seismic waves moving deep inside the Earth, surface waves move just like waves in the water below the Earth's surface. Surface waves are the slowest seismic waves and the last waves to strike an area after an earthquake. First, P-waves undergo compression through the deeper layers of the Earth. They result in minimal damage. The second group of waves is the S-waves. They start deep in the earth and move up and down. Strong S-waves do some damage when they reach the surface. Surface waves run in the past. Their slow roll under the surface provides the greatest risk for loss of man-made structures and changes in natural landforms.
An earthquake is an accidental vibration on the ground surface that results from an adjustment due to the resilience or topography of rocks in the ground. This can happen for both natural and human reasons. Among the natural causes, volcanic action, tectonic instability, equilibrium attempts, folding and pension are plutonic, it is called Epi-center. Incidence and dispersion of geological gases etc. are included.
According to the Road Elastic-Resurrection Principle, each rock has an ability to bear stress. After that if the tension force becomes more, the rock breaks and the broken part comes back to its place. In this way, rocks are prone to earthquakes and earthquakes occur. Artificial or man-made earthquakes are the result of unscientific human actions. In this context, the construction of roads, dams, large reservoirs, etc. in tectonically unstable regions can be taken. In addition, nuclear tests are also responsible for earthquakes. The amount of 'radon' gases in the atmosphere increases before an earthquake strikes. Therefore, the increase in the quantity of this gas is a sign of an earthquake in that particular region. The place where seismic waves originate is called 'Focus' and where seismic waves are first experienced.
The energy that comes out of the earthquake during this earthquake is called 'Elastic Energy'. During an earthquake, several types of seismic waves are generated which can be classified into three categories:
- Primary or Longitudinal Waves: These are also called 'P' waves. These are longitudinal waves and move like sound waves. This is the fastest speed among the three seismic waves. It can move in a solid as well as in a liquid medium, although its speed is slower in the liquid medium than in the solid. It has a speed of 66% higher than 'S' waves.
- Secondary or Transverse Waves: They are also called "S 'waves. They move like light waves. They can only move in a solid medium, often disappearing in a liquid medium. Since this earth, K does not pass through the core, so the 'S' waves are estimated in relation to the Earth's core being liquid. It has a 40% lower speed as compared to 'P' waves.
- Surface or Long Period Waves: These are also called 'L' waves. It affects only the upper part of the earth. These are highly effective waves and go the longest route. Their speed is very slow and reaches late time, but their effect is most devastating.
Hence, the correct answer is option b.
'P' and 'S' waves move in pairs. P - S has the highest speed; The speed of Pg - Sg is minimal while the speed of P * - S * is between the two. Information about the interior of the earth can be obtained on the basis of the movement and path of these waves.