Seismic Anatomy
Depth
Converting TWT to depth is not a simple procedure, however it is possible to give a general idea of the depth a seismic profile can show by using an average velocity for all the rocks. In the profile shown here, we can allocate an average seismic velocity of 6000m/s for the data between 0 and 1200ms.
Calculate the depth at 1200ms.
If we zoom up part of the seismic profile, we can see at about 800ms TWT a strong set of 3 seismic reflectors, blue-red-blue (peak-trough-peak). The TWT for this sequence (only the thickness of the blue-red-blue part) is 50ms, and the velocity is 6000m/s. Using the same equations as before, this gives a thickness of 150m to this set of reflectors.
Think about how much geological detail you would see in a 150m high sandstone cliff (how many individual beds for example). Hopefully you can now see the seismic is not the same as a cross section. The closest distance two features can be together and still be seen separately on seismic is about 10m, and this would only be possible near to the surface.
