A highly explosive source is input in an elastic-brittle rock mass and the resulting near-source complexities are considered. This study is undertaken with a three-dimensional numerical model similar to the discrete element method. This model can simulate the creation of the damage zone with the associated block motions as well as the elastic wave propagation. Free-field ground motion data are recorded to determine the reduced displacement potential (RDP). In a fully elastic numerical model, as expected, the RDP computation corresponds to the analytical one-dimensional problem of a spherically symmetric explosive source acting in a homogeneous elastic medium. When fracturing occurs, during the creation of the damage zone, block motions are observed, and the RDP computations are affected. For an ideal system which conserves energy, the potential elastic energy is converted to kinetic energy during the fracturing process resulting in an apparent RDP which is larger than in the homogeneous elastic case. This three-dimensional approach is undeniably advantageous where a global description of the heterogenous effects of block motions and the continuous aspects of wave propagation are considered simultaneously. ¿ American Geophysical Union 1996