Abstract: A system and computer program for determining the location of a seismic event in an earth formation zone using seismic traces corresponding to the event collected from one or more sensors in the zone. A graphical data window is displayed of the seismic traces corresponding to the event, the traces representing observed arrival time signals from the sensors plotted with respect to time. A window of a base map of the positions of the sensors within the zone is also displayed. Displayed in the data window is a curve plotting calculated arrival time signals for the traces, the curve being developed from a user-selected one of the observed arrival time signals displayed in the data window and from a user-selected trial location of the event selected in the base map window. The program enables user-repositioning of the trial location in the base map window such that the displayed curve moves in correspondence with the repositioning of the trial location.