Systems, methods, and instructions encoded in a computer-readable medium can perform operations related to refining information on characteristics of natural fractures of a subterranean formation. Fracture pattern models are generated based on sampling an initial distribution of values for a fracture parameter. Each fracture pattern model may include, for example, a model of natural fractures in a subterranean formation. Each fracture pattern model is compared to microseismic event data for a subterranean region. A refined distribution for the fracture parameter is generated based on the comparison. Generating the refined distribution may include, for example, selecting values of the fracture parameter from fracture pattern models that correlate with the microseismic event data. In some implementations, an injection treatment may be simulated and/or designed based on the refined distribution.