The Effect of Velocity Uncertainty on a Noraml Incidence VSP Image

We present a method to evaluate and interpret the effect of velocity uncertainty on the spatial location of a Normal Incidence VSP image. A set of velocity models, all acceptable, is automatically generated. Then a seismic image is computer for each velocity model and with the same upgoing wavefield. Finally each image is compared to an image of reference and the uncertainty on position is estimated from the variability of the local displacements. This method is applied to a dataset from the North Sea and results are commented.