Application of seismic interferometry to imaging a crystalline rock environment at an active VMS mine in Flin Flon, Manitoba, Canada

Seismic interferometry is a technique by which the Green’s function or impulse response between two receivers is recovered through the cross-correlation of the transmission responses recorded by those receivers. This technique has found several applications, including the generation of virtual shot gathers from ambient seismic noise for use in seismic reflection processing. In March of 2013, 336 receivers were deployed over the volcanogenic massive sulphide (VMS) deposit found at the Lalor mine in Manitoba, Canada. Approximately 300 hours of ambient seismic noise was recorded for the purpose of testing the effectiveness of seismic interferometry in imaging a crystalline rock environment. A time-domain beamforming algorithm was implemented to determine the locations of the sources present during recording. The results indicate that the vast majority of the recorded noise originated from mine and ventilation shafts located at the Lalor mine. Synthetic experiments were conducted to determine the effects such a source distribution would have on the application of seismic interferometry in the presence of dipping reflectors. The experiments show that if sources are located only on one side of a receiver line, the dip and lateral extents of reflectors will not be imaged properly. A technique involving beamforming and F-K filtering was developed to remove surface wave noise originating from near-field sources. Using this technique, the raw data was processed into virtual shot gathers free of surface wave noise. Virtual shot gathers were generated along 4 of the receiver lines and processed as separate 2-D reflection datasets. The resulting reflection profiles are compared against coincident DMO-stacked data from a larger 3-D active seismic survey conducted over the Lalor mine. Using this comparison in conjunction with knowledge of the local geology, events recovered in the passive reflection profiles are interpreted as either real reflections or spurious events, and possible explanations of their origin are given.