1. A method for determining a seismic event from indications of seismic noise, the method comprising: receiving seismic trace data responsive to the seismic noise generated within a formation at sensors at a plurality of locations; and using a processor to: determine a virtual trace from the seismic trace data for a virtual trace location related to the plurality of locations, and determine a virtual trace value (E Rvirtual ) for the determined virtual trace from normalized values of the seismic trace data and a normalized value of the determined virtual trace, wherein the virtual trace value indicates a presence of the seismic event.