3.1.4. Earthquake Waves

All natural earthquakes take place in the lithosphere. The lithosphere refers to the portion of depth up to 200 km from the surface of the earth. An instrument called ‘seismograph’ records the waves reaching the surface.

Earthquake waves are generated from the energy released during earthquakes. These waves travel through the lithosphere, which is the outer solid layer of the Earth, extending up to 200 kilometers. To study these waves, scientists use a seismograph, a sensitive instrument that records the vibrations caused by these waves, providing crucial data about the earthquake's magnitude and impact.

Think of the lithosphere like the skin of an apple. When you press down on the apple, it creates waves that ripple through the fruit. Similarly, an earthquake creates waves that ripple through the earth, and a seismograph acts like a camera that captures these ripples.

Earthquake waves are basically of two types — body waves and surface waves. Body waves are generated due to the release of energy at the focus and move in all directions travelling through the body of the earth. The body waves interact with the surface rocks and generate new set of waves called surface waves.

There are two main types of earthquake waves: body waves and surface waves. Body waves travel through the Earth's interior and can be further divided into two types: P-waves (primary waves), which are faster and can move through solids, liquids, and gases, and S-waves (secondary waves), which are slower and can only travel through solids. Surface waves, on the other hand, move along the Earth's surface and typically cause more damage because they arrive last and have more amplitude.

Imagine throwing a stone into a pond. The ripples that form as the water moves outward represent body waves traveling through different layers of the Earth. The bigger waves that reach the edges of the pond and cause splashes can be compared to surface waves, which often lead to the most damage during an earthquake.

Different types of earthquake waves travel in different manners. As they move or propagate, they cause vibration in the body of the rocks through which they pass. P-waves vibrate parallel to the direction of the wave. S-waves create troughs and crests in the material through which they pass.

As earthquake waves propagate through the Earth, they cause vibrations in the rocks around them. P-waves compress and expand the rocks they travel through, similar to how a slinky moves when pushed or pulled. S-waves move perpendicular to their propagation direction, creating up-and-down movements in the material, which can create a more noticeable shaking effect on the surface.

Imagine a crowd of people at a concert clapping their hands. The P-waves behave like the claps, creating a compressing wave of sound that travels through the air. In contrast, the S-waves are more like the bobbing movement of the crowd when they sway side to side, leading to stronger vibrations felt nearby.