Seismic data is used to visualize the Earth's sub surface. This is achieved by measuring travel times of reflections from pressure waves propagating through the ground. Seismic data and interpretations of seismic data will therefore often have z values in travel time, not depth. In order to get a depth value for a travel time value, we need to do a depth conversion. A depth conversion combines the velocity of the pressure wave with the travel time to get a depth value.
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When going from top to bottom, the layer velocity model will initially use the water velocity as interval velocity until it meets the top horizon. From the top horizon it will use the top horizon velocity as interval velocity until it meets the next horizon, continuing this pairwise matching of successive horizons for the rest of the horizonsseismic data.
During depth conversion the interval velocities are used to calculate an average velocity.
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