A system for processing an earth model of a geological volume of interest, the system comprising: one or more processors configured to execute computer program modules, the computer program modules comprising: an earth model module for obtaining the earth model of the geological volume of interest, wherein the earth model includes a polygon mesh that describes a position of a surface within the geological volume of interest, the polygon mesh being comprised of planar polygons defined by three or more vertices, and the earth model including positional coordinates for the vertices of the polygons; a dip module for determining values of the dip of the polygon mesh within the earth model, wherein determining values of the dip of the polygon mesh includes determining values of dip for the individual polygons based on the positional coordinates of the vertices defining the polygons, wherein the values of dip for the individual polygons are vectors which define the surface normal directions of those individual polygons with respect to a reference direction; a smoothing module configured to smooth the determined values of dip along the polygon mesh to generate corresponding smoothed vectors without altering the positional coordinates for the vertices of the polygons, the smoothed vectors defining how seismic energy propagating in the earth model reflects and refracts at the surface; and a ray-tracing module configured to trace rays through the earth model, wherein the ray-tracing module uses the positional coordinates for the vertices of the polygons and the smoothed vectors along the polygon mesh in determining one or more of (a) a refraction of rays caused by the surface or (b) a reflection of rays caused by the surface. an earth model module for obtaining the earth model of the geological volume of interest, wherein the earth model includes a polygon mesh that describes a position of a surface within the geological volume of interest, the polygon mesh being comprised of planar polygons defined by three or more vertices, and the earth model including positional coordinates for the vertices of the polygons; a dip module for determining values of the dip of the polygon mesh within the earth model, wherein determining values of the dip of the polygon mesh includes determining values of dip for the individual polygons based on the positional coordinates of the vertices defining the polygons, wherein the values of dip for the individual polygons are vectors which define the surface normal directions of those individual polygons with respect to a reference direction; a smoothing module configured to smooth the determined values of dip along the polygon mesh to generate corresponding smoothed vectors without altering the positional coordinates for the vertices of the polygons, the smoothed vectors defining how seismic energy propagating in the earth model reflects and refracts at the surface; and a ray-tracing module configured to trace rays through the earth model, wherein the ray-tracing module uses the positional coordinates for the vertices of the polygons and the smoothed vectors along the polygon mesh in determining one or more of (a) a refraction of rays caused by the surface or (b) a reflection of rays caused by the surface.