Seismic refraction methods rely on which property difference?

Seismic refraction methods rely on which property difference?

• A. Seismic wave reflection
• B. Wave attenuation
• C. Pore pressure differences
• D. The differential seismic velocities

Answer: (D)

Seismic refraction methods depend on a difference in seismic velocities between adjacent layers. When a wave in the slower upper layer encounters a boundary with a faster lower layer at a sufficient angle, energy is refracted along that boundary and then returns to the surface as a head wave. This head wave travels through the deeper, faster layer and arrives at the surface as the first detectable signal at larger distances. The travel-time of these arrivals increases linearly with distance, with a slope that reflects the velocity of the deeper layer, and the intercept provides information about the depth to the boundary. Because the method relies on the velocity contrast between layers, not on reflection strength, attenuation, or pore pressures, it uniquely leverages this property difference to reveal subsurface structure.

Seismic refraction methods depend on a difference in seismic velocities between adjacent layers. When a wave in the slower upper layer encounters a boundary with a faster lower layer at a sufficient angle, energy is refracted along that boundary and then returns to the surface as a head wave. This head wave travels through the deeper, faster layer and arrives at the surface as the first detectable signal at larger distances. The travel-time of these arrivals increases linearly with distance, with a slope that reflects the velocity of the deeper layer, and the intercept provides information about the depth to the boundary. Because the method relies on the velocity contrast between layers, not on reflection strength, attenuation, or pore pressures, it uniquely leverages this property difference to reveal subsurface structure.