A goal of seismic processing is to verify the spatial characteristics of the subsurface. Achieving this goal often requires human analysis to interpret geologically meaningful discontinuities from the seismic image. This interpretation is a challenging task even for an experienced interpreter if the image is 3D. This paper introduces an automatic method to extract seismic event discontinuities from a 3D seismic image. The proposed method consists of three steps. The first step is to evaluate the coherency of seismic events from the seismic image. The second step is to express the regions where discontinuities may exist in a binary image form. The third step is to locate the discontinuity surfaces by thinning the region found in the second step.