A method of seismic surveillance above a region of the subsurface of the earth containing structural or stratigraphic features conducive to the presence, migration, or accumulation of hydrocarbons, comprising the steps of: (a) accessing a plurality of seismic receivers positioned proximate to the region of the subsurface of the earth; (b) at a location proximate to said plurality of receivers, (bl)continuously recording a signal from each of said plurality of seismic receivers for a predetermined period of time, thereby obtaining a plurality of passive seismic recordings, and, processing in near real time at least a portion of said plurality of passive seismic recordings by applying a low-pass filter to each of said plurality of passive seismic recordings and decimating each of said plurality of passive seismic recordings by a predetermined factor of at least 10 to produce a plurality of virtual-source gathers, wherein said plurality of virtual source gathers have a storage size that is substantially less than a storage size of said at least a portion of said plurality of passive seismic recordings; (c) transmitting at least a portion of said plurality of virtual source gathers to a remote processing facility; (d) within said remote processing facility, further processing at least a portion of said plurality of virtual source gathers to obtain an image representative of at least a portion of the region of the subsurface of the earth; and, (e) using at least a portion of said image to explore the region of the subsurface of the earth. (a) accessing a plurality of seismic receivers positioned proximate to the region of the subsurface of the earth; (b) at a location proximate to said plurality of receivers, (bl)continuously recording a signal from each of said plurality of seismic receivers for a predetermined period of time, thereby obtaining a plurality of passive seismic recordings, and, processing in near real time at least a portion of said plurality of passive seismic recordings by applying a low-pass filter to each of said plurality of passive seismic recordings and decimating each of said plurality of passive seismic recordings by a predetermined factor of at least 10 to produce a plurality of virtual-source gathers, wherein said plurality of virtual source gathers have a storage size that is substantially less than a storage size of said at least a portion of said plurality of passive seismic recordings; (bl)continuously recording a signal from each of said plurality of seismic receivers for a predetermined period of time, thereby obtaining a plurality of passive seismic recordings, and, processing in near real time at least a portion of said plurality of passive seismic recordings by applying a low-pass filter to each of said plurality of passive seismic recordings and decimating each of said plurality of passive seismic recordings by a predetermined factor of at least 10 to produce a plurality of virtual-source gathers, wherein said plurality of virtual source gathers have a storage size that is substantially less than a storage size of said at least a portion of said plurality of passive seismic recordings; (c) transmitting at least a portion of said plurality of virtual source gathers to a remote processing facility; (d) within said remote processing facility, further processing at least a portion of said plurality of virtual source gathers to obtain an image representative of at least a portion of the region of the subsurface of the earth; and, (e) using at least a portion of said image to explore the region of the subsurface of the earth.