Path effects represent relative changes in amplitude and phase that occur when elastic waves propagate in different directions within a medium. Path effects for downhole microseismic monitoring differ fundamentally from path effects for surface monitoring. The reason for this difference is simple: in most cases, borehole microseismic recordings consist of waves transmitted in a more-or-less horizontal direction, whereas surface microseismic data typically contain signals traveling in the vertical direction. In many geologic settings of so-called tight reservoirs this is equivalent to parallel and perpendicular to the layering.