1. A method of analysing an underground seismic event comprising: performing a hydraulic fracturing which causes a seismic event; receiving and measuring seismic waves emitted by the seismic event using one or more seismic data recording devices; converting the measurements of the seismic waves using a digital computer into a value for magnitude of explosion or implosion, a value for magnitude of displacement discontinuity at a plane, the direction of a normal to that plane, and a direction of displacement; where the two said values and the two said directions compose a whole moment tensor describing the seismic event; outputting the two said values and the two said directions; and analyzing the underground seismic event caused by the hydraulic fracturing.