Abstract. Although tsunamis generated by submarine mass failure are not as common as those induced by submarine earthquakes, sometimes the generated tsunamis are higher than a seismic tsunami in the area close to the tsunami source, and the forecast is much more difficult. In the present study, reciprocal Green's functions are proposed as a useful tool in the forecast of submarine landslide tsunamis. The forcing of the continuity equation due to depth change in a landslide is represented by the temporal derivative of the water depth. After a convolution with the reciprocal Green's function, the tsunami waveform can be obtained promptly. Thus, various tsunami scenarios can be considered once a submarine landslide happens, and a useful forecast can be formulated. When a submarine landslide occurs, the various possibilities for tsunami generation can be analyzed, and a useful forecast can be devised.