1. A computer-implemented method for identifying dominant fracture orientations in a subterranean zone, the method comprising: determining a basic plane orientation for each of a plurality of basic planes defined by microseismic event data, the microseismic event data associated with a fracture treatment of a subterranean zone, the basic planes defined by coplanar subsets of microseismic events; calculating, by data processing apparatus, the quantity of the basic plane orientations in each of a plurality of orientation ranges; and identifying a dominant fracture orientation for the subterranean zone based on one or more of the identified quantities.