The Virtual Source Method: An Interferometric Approach to Imaging and Monitoringthe Earth's Subsurfa

The virtual source method is an geophysical techniqueto image and monitor the Earth's subsurface below acomplicated and time-varying overburden without theknowledge of overburden velocities and near-surfacechanges. It is based on extracting the responsebetween a given pair of receivers by correlating thewavefields recorded by them and stacking over thephysical sources. The virtual source method requiressurface shooting recorded by subsurface receiversplaced below the distorting or changing part of theoverburden. Redatuming the recorded response to thereceiver locations allows the reconstruction of acomplete downhole survey as if the sources were alsoburied at the receiver locations. The ability toredatum the data independent of the knowledge ofcomplicated and time-varying overburden velocitiesmakes the virtual source method a valuable tool forimaging and time-lapse monitoring.