Using the direct seismic responses of fractures and fracture zones in productive formations to obtain information about their locations and characteristics is an essentially new and promising direction of investigation. Given the growing production of hydrocarbons from unconventional reservoirs, the basic understanding of seismic wave responses of natural and hydraulic fractures is urgently needed, and the ability to model those waves is a necessary first step toward detection and more accurate characterization of fractured reservoirs and through this process toward improved oil production....