A velocity anomaly zone with high contrasts and small wave length variations is often a challenge for conventional depth imaging. It requires model details that are usually being smoothed out because of the noise present in the data. Over our project area in the Eastern Gulf of Mexico, as shown in Figure 1, carbonate karst zones are often found over the Florida Escarpment area. The karst zones have significantly slower velocities than the surrounding sediments. The size of these karsts is usually a few meters to a few hundred meters. The resulting seismic images below the karst zones are often poor and non-geological (Figure 2). A synthetic modelling study has been conducted to give more insights into the difficulty of the conventional tomography, and to provide some guidelines for modelling the karst zone velocity anomaly. A new velocity model building technique has been developed by combining the karst modelling and the horizon-driven tomography. The geological information and interpretation are used as input as well as constraints to seismic tomography. The integration of geological interpretation and seismic tomography enable us to derive a detailed velocity model and improve the seismic image in the area.