Systems, methods, and instructions encoded in a computer-readable medium can perform operations related to simulating subterranean fracture propagation. A subterranean formation model representing rock blocks of a subterranean formation is received. The subterranean formation model is used to predict a response of each rock block to one or more forces acting on the rock block during an injection treatment for the subterranean formation. The predicted responses of the rock blocks may include, for example, a fracture, a rotation, a displacement, a dilation of an existing fracture, and/or another type of response. In some implementations, an injection treatment may be designed for a subterranean formation based on the predicted response of the rock blocks.