Refraction

Definition

Refraction is the bending of seismic waves as they pass through different layers of the Earth's interior, caused by variations in wave speed due to changes in material properties. This phenomenon is crucial for understanding how seismic waves travel and interact with different geological structures, which aids in identifying seismic phases, analyzing travel time curves, and interpreting seismograms.

5 Must Know Facts For Your Next Test

1. Refraction plays a key role in determining the paths that seismic waves take as they encounter layers with different densities and elastic properties within the Earth.
2. Seismic wave velocities generally increase with depth due to the increasing pressure and density of Earth's materials, leading to significant refraction effects.
3. Refraction is essential for distinguishing between seismic phases such as primary waves (P-waves) and secondary waves (S-waves) in seismograms.
4. Travel time curves illustrate how the arrival times of refracted waves vary based on their paths and the characteristics of the materials they traverse.
5. Understanding refraction allows seismologists to infer information about the Earth's internal structure, including the composition and state of various layers.

Review Questions

• How does refraction contribute to our understanding of seismic phases and their identification?
  • Refraction helps us identify seismic phases by showing how seismic waves change direction when they encounter different geological materials. When P-waves or S-waves enter a new layer at a certain angle, their velocities change, causing them to bend. This bending creates distinct arrival times on seismograms that correspond to different seismic phases, allowing seismologists to interpret what layers are present in the Earth's interior based on the observed data.
• Discuss how refraction affects the travel time curves of seismic waves and what this implies about Earth's internal structure.
  • Refraction significantly influences travel time curves by altering the paths taken by seismic waves as they move through varying layers of material. As waves enter denser materials at an angle, they speed up and bend toward the normal, creating longer travel paths. This change in path leads to specific patterns in travel time curves, which can be analyzed to infer details about the composition, density, and state of different layers within the Earth.
• Evaluate how understanding refraction enhances our interpretation of Earth's internal composition from seismic imaging techniques.
  • Understanding refraction allows us to interpret Earth's internal composition more accurately by utilizing seismic imaging techniques like tomography. By analyzing how seismic waves are refracted at boundaries between different materials, we can create detailed images of subsurface structures. This information is crucial for identifying not only the layering but also the physical properties of those layers, such as whether they are solid or liquid. As a result, we gain insights into complex features like the mantle-core boundary and the distribution of various rock types beneath the surface.

Related terms

Seismic Wave Velocity: The speed at which seismic waves travel through different materials, which varies based on density and elastic properties.

Critical Angle:

The specific angle of incidence at which seismic waves are refracted along a boundary between two materials, leading to phenomena like wave conversion.

P-waves and S-waves: Types of body waves; P-waves are compressional waves that travel faster through the Earth, while S-waves are shear waves that travel more slowly and cannot move through liquids.