The methods described are for determining distribution, orientation and dimensions of networks of hydraulically-induced fractures within a subterranean formation containing fluids. Micro-seismic events are generated by particles introduced into the fractures which are capable of explosive or chemical reaction. In one method, treated proppant having a reactive coating is positioned in the formation during fracturing and reactive particles are introduced. In another method, reactive particles having a reactive core and a non-reactive coating are positioned in the fractures and react upon removal of the non-reactive coating, such as by dissolving, and reaction with a reactive particle. The waves generated by the micro-seismic events are used to map fracture space.