Shotpoint and CDP or CMP geometry Question 1 (I) 60% with a 50-50 split on the work shown and the correct numerical answer (II) 20% (III) 20 % Number of channels or receiver groups Shot spacing (m) Receiver spacing (m) CMP spacing (m) Maximum Fold 6 25 25 12.5 3 48 25 25 12.5 24 60 25 25 12.5 30 60 25 50 25 60 60 25 100 50 30 6 25 100 50 3         When the shotpoint Spacing = Twice the CMP spacing then the maximum fold (as seen above) is equal to half the number of geophones   When the shotpoint spacing = CMP spacing, the maximum fold is equal to the number of geophones ( shown immediately above) (c) When the shotpoint spacing is less than half CMP spacing, e.g. 1/4, (immediately above), the linear density of CMP's increases but the maximum fold is the same as if the shotpoint spacing were twice the CMP spacing. One way of viewing the control of subsurface fold by shotpoint and geophone spacing is to focus on the ratio of shotpoint-to-CMP spacing. For example, if the shotpoint spacing is equal to the CMP spacing then for every shot that the geophone array is moved forward the CMP advances by the same interval and directly over a pre-existing CMP thereby increasing the fold by one. If the shotpoint spacing is twice as long as the CMP spacing then with every successive shot the whole array is moved forward a distance equal to two CMP spacings and missing one in between so that the fold can only be half as great as the previous case