Question

What are the slowest seismic waves? A) surface C) secondary B) primary D) pressure

Short answer

The slowest seismic waves are surface waves (A).

Step-by-step solution

Understand Seismic Wave Types

Seismic waves are waves of energy that travel through the Earth and are typically generated by earthquakes. There are three main types of seismic waves: Primary (P-waves), Secondary (S-waves), and Surface waves.

Identify Primary and Secondary Waves

Primary waves, also known as P-waves, are compressional waves that travel through solids, liquids, and gases. They are the fastest type of seismic wave. Secondary waves, or S-waves, are shear waves that move only through solids and are slower than P-waves.

Understand Surface Waves

Surface waves travel along the Earth's surface rather than through its interior. These waves are typically slower than both P-waves and S-waves, and they are responsible for most of the damage during an earthquake.

Compare Wave Speeds

Among the seismic waves, P-waves are the fastest, followed by S-waves. Surface waves are the slowest among the three. Therefore, the choice that describes the slowest seismic waves corresponds to Surface waves, which is option A.

Key concepts

P-waves

P-waves, or Primary waves, are the initial waves generated by an earthquake. These waves lead the seismic activity as they move through the earth's layers. Unlike other types, P-waves can travel through a variety of materials including solids, liquids, and gases. Their ability to move swiftly through different mediums is due to their compressional nature. This means they push and pull the ground in the direction they are traveling.

This compressive action is similar to the motion of a coiled spring being squeezed and released. Due to this efficient movement, P-waves often arrive first at seismic recording stations, allowing scientists to quickly assess initial earthquake data. Key features of P-waves include:
- Being the fastest seismic waves.
- Traveling through solids, liquids, and gases.
- Having a push-pull motion.

S-waves

Secondary waves, or S-waves, follow P-waves and are the second type of seismic waves to be detected after an earthquake. Unlike P-waves, S-waves can only travel through solids. This restriction arises because S-waves are transverse waves, moving the ground perpendicular to their direction of travel.

This side-to-side motion is akin to the ripples seen when a rope is sharply flicked. Because they are slower than P-waves, S-waves take more time to reach seismic stations, offering additional data to further analyze the earthquake's impact. Important characteristics of S-waves include:
- Being slower than P-waves but faster than surface waves.
- Traveling only through solid materials.
- Having a side-to-side oscillation.

Surface waves

Surface waves are the last to arrive during an earthquake and are known for their destructive potential. Unlike P-waves and S-waves, surface waves travel along the Earth's surface rather than its interior. This results in two types of motions: Love waves and Rayleigh waves.

- **Love waves** cause horizontal shifting of the ground, much like a snake slithering - **Rayleigh waves** create a rolling motion, similar to ocean waves

These movements shake buildings side-to-side and up-and-down, causing significant damage during earthquakes. The slow speed of surface waves does not diminish their impact; rather, it allows them to sustain powerful vibrations over longer periods. This is why surface waves are commonly responsible for the majority of the visible damage during seismic events. Key insights into surface waves include:
- Being the slowest type of seismic wave.
- Having two main types: Love and Rayleigh.
- Traveling across the Earth's surface, contributing heavily to earthquake damage.