A-031 A CAUSALITY BASED IMAGING METHOD Summary H. POOT J.T. FOKKEMA and C.P.A WAPENAAR Delft University of Technology Subfaculty of Applied Earth Sciences Mijnbouwstraat 120 2628 RX Delft An imaging condition is derived based on the causality principle. This condition determines directly the velocity contrast over an interface using the wavefields measured at this interface. We assume the velocity below the interface is constant in vertical (but not necessarily in lateral) direction for a thin layer. Using the reciprocity theorem we can now calculate the wavefield below this thin layer in the case it was removed and replaced by a