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[[file:interpreting-seismic-data_fig12-6.png|thumb|300px|{{figure number|1}}Example of a zero-offset VSP. Copyright: Landmark Graphics.]]

[[file:interpreting-seismic-data_fig12-6.png|thumb|300px|{{figure number|1}}Example of a zero-offset VSP. Copyright: Landmark Graphics.]]

A [http://wiki.seg.org/wiki/Dictionary:Vertical_seismic_profiling_%28VSP%29 vertical seismic profile (VSP)] yields the best connection between geologic horizons and seismic events. It is recorded by using a source at the surface and many receiver locations down a wellbore, or vice versa. The receivers record full traces for interpretation. The receiver spacing is usually [[length::10 ft]]. This gives actual traveltimes from the surface to points in the earth, and it is the best and most direct method of associating seismic events with geological horizons. The kind of VSP shown in [[:file:interpreting-seismic-data_fig12-6.png|Figure 1]] (produced by commercial software) is often called a zero-offset VSP, meaning that only a single source position is used as close to the wellhead as possible. It is relatively inexpensive. There are also multioffset and multiazimuth VSPs, which use many source locations. These are much more expensive and sometimes are useful for local, high-resolution imaging. However, a zero-offset VSP is sufficient for event identification and 3-D seismic calibration.

A [http://wiki.seg.org/wiki/Dictionary:Vertical_seismic_profiling_%28VSP%29 vertical seismic profile (VSP)] yields the best connection between geologic horizons and seismic events. It is recorded by using a source at the surface and many receiver locations down a wellbore, or vice versa. The receivers record full [http://wiki.seg.org/wiki/Dictionary:Seismic_trace traces] for interpretation. The [http://wiki.seg.org/wiki/Dictionary:Receiver receiver] spacing is usually [[length::10 ft]]. This gives actual [http://wiki.seg.org/wiki/Dictionary:Traveltime traveltimes] from the surface to points in the earth, and it is the best and most direct method of associating seismic events with geological horizons. The kind of VSP shown in [[:file:interpreting-seismic-data_fig12-6.png|Figure 1]] (produced by commercial software) is often called a zero-offset VSP, meaning that only a single source position is used as close to the wellhead as possible. It is relatively inexpensive. There are also multioffset and multiazimuth VSPs, which use many source locations. These are much more expensive and sometimes are useful for local, high-resolution imaging. However, a zero-offset VSP is sufficient for event identification and [[3-D seismic data: the data cube|3-D seismic data]] calibration.

==Velocities from sonic logs==

==Velocities from sonic logs==