Velocity Uncertainty

The use of the Dix equation to convert RMS stacking velocities to interval velocities is based on the assumption of horizontal layers and constant velocities between the layers. Therefore, dipping structure and vertical and lateral velocity variations can introduce significant errors into the resulting interval velocity fields Hajnal and Sereda (1981); Hubral and Krey (1980); Toldi (1985). Furthermore, the error in interval velocity is inversely proportional to the time thickness to depth ratio for the reflector interval under consideration. Because of the relatively deep water layer (more than 3 km) and the small dips of the sediments in the data used, most of the errors in the interval velocities will be caused by picking errors in the rms velocities and the small thickness between the reflectors with respect to the water depth.

 

rms1
Figure 8 The left panel shows the velocity scan overlain by the picked RMS velocity trend. The middle panel displays the velocity scan contours again overlain by the RMS velocity. The right panel shows the moveout-corrected CMP gather using the displayed RMS velocity.

 

vel1 Figure 9 Interval velocity obtained from the RMS velocity function shown in Figure 2.7.

 

error
Figure 10 The left panel shows the error in the RMS velocity trend. The solid line represents the original velocity; the two dashed lines are the velocities with picking errors of $\pm$ 10 m/s. The right panel displays the interval velocities resulting from the different RMS velocity trends. It represents the expected error in interval velocities.