where

where is the vertical 2-way time through the

Plugging equation 1.5 into 1.4
and truncating after 2 terms yields
the traveltime equation for short offsets and a multilayered
media:

The approximation in the above equation is valid for small values of offset

V^{2}_{n} |
= | (1.7) |

where

In summary we have learned some new words.

1. STATION: Recording site connected to a group of geophones. Data from
this site is transmitted along one channel in recording line.

2. GEOPHONE Group: Geophones serially connected, and summed signal is fed to one channel.

3. SPREAD LENGTH: Length of recording line.

4. ZO SECTION: Seismic traces obtained by
recording seismic energy with a geophone that has zero offset from the source.

5. CSG: Common shot gather of traces recorded with a common shot.

6. CMG: Common midpoint gather of traces where each of the traces
have the same midpoint position between the shot and receiver.

7. SHOT AND GROUP INTERVALS: Intervals between shot points and stations.

8. APPARENT VELOCITY: Velocity of an arrival as measured along a horizontal line.

9. ENDLINE AND MIDPOINT RECORDING GEOMETRIES: Shot at end of recording line = endline. Shot at
midpoint of recording line = midpoint.

10. The fold number is the number of traces in a CMG. It is
the number of traces in a gather with a common reflection point.