Figure 2. Illustration of the transmission of seismic energy through the subsurface. In order for seismic refraction to be successful, the thickness and density and velocity must increase with depth. Unsaturated sand and gravel commonly has seismic velocities of about 1500 feet/second whereas water-saturated sand and gravel is typically around 5000 feet/second and bedrock has velocities of 10,000 feet/second or greater. Modified from Haeni, 1988.

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Last updated on October 6, 2005

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