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# Mains Practice Questions

• Q. What are seismic waves? Give a detailed account of different types of seismic waves.

### Approach

• Start the answer by introducing the origin of seismic waves and their types.
• Discuss the different types of seismic waves and their characteristics.
• Conclude Suitably.

### Introduction

During an earthquake seismic waves are generated which spread outwards in all directions from the focus. Seismic waves are of three types (i) P waves or Primary Waves, (ii) S Waves or Secondary Waves, and (iii) L Waves or Surface Waves.

### Body

Types of Seismic Waves and their Characteristics

• P-Waves:
• These are compressional waves which cause the particles of rock to vibrate in the longitudinal direction.
• The P waves travel fastest, therefore they reach a seismic station first
• Their velocity is 1.7 times than that of S waves
• They pass through solids as well as liquids.
• S-Waves:
• These are shear waves which are transverse in nature.
• These can only pass through solids.
• L-Waves or Surface Waves:
• When P and S waves reach the earth's surface, they are converted into L waves.
• The L waves travel along the surface and cause earthquakes.
• They are transverse in nature and their velocity is much less than the P and S waves.

### Conclusion

Surface waves are responsible for causing earthquakes while the main significance of P and S waves is in the study of the earth's interior. P and S waves travel through the interior of the earth and are reflected and refracted as they enter a layer of different material.