Hydraulic fracturing is an important tool that helps extract fluids from the subsurface. It is critical in applications ranging from enhanced oil recovery to geothermal energy production. As the goal of fracturing is to increase flow rates within the reservoir volume, and because the reservoir is typically heterogeneous, several fractures are often created. Because of confining stresses, most fractures that have been created and remain open are nearly vertical (Zoback et al., 2003). Creating a set of almost parallel fractures is quite common in situations with smoothly varying stress (Figure 1).