A system for monitoring fluid pathways in a producing hydrocarbon reservoir of the type in which injected water replaces extracted oil, thereby generating passive microseismic events, wherein the reservoir includes at least one borehole associated with the reservoir, the system comprising: a first sensor network comprising a number of 3-component seismic sensors physically secured to the ground within a sensor area surrounding the borehole; a second sensor network comprising a number of 3-component seismic sensors installed permanently at various levels in the well borehole; a high precision Global Positioning System, GPS, clock time measurement system and wherein the system is configured to detect passive microseismic events for said first and second seismic sensor networks simultaneously in a time synchronous mode using the clock time measurement system and generate corresponding microseismic data; a computer configured to record said microseismic data of said first and second seismic sensor networks, wherein said computer is programmed to: sum said recorded microseismic data received from the first sensor network over time windows and apply a seismic migration analysis to determine the position of the microseismic events in space using an overburden layer velocity method, and analyze a grid-based volume of migrated seismograms to determine the origin time of the microseismic source; detect, based on said recorded microseismic data time synchronously detected from said second sensor network, compressional P-wave and shear S-wave events, estimate arrival times of microseismic events and perform an auto-search around the estimates to obtain refined origin times of the microseismic events, and determine, using the P-wave and S-wave events, the source location at each origin time of the detected microseismic event; compare the source location and origin determinations from the first and second sensor networks and determine a resultant location and origin time of the microseismic event; and map failure surfaces which define pathways for preferential fluid movement in the reservoir based on the resultant location and origin time determinations; and an output device for displaying a mapping of failure surfaces which define pathways for preferential fluid movement in the reservoir. a first sensor network comprising a number of 3-component seismic sensors physically secured to the ground within a sensor area surrounding the borehole; a second sensor network comprising a number of 3-component seismic sensors installed permanently at various levels in the well borehole; a high precision Global Positioning System, GPS, clock time measurement system and wherein the system is configured to detect passive microseismic events for said first and second seismic sensor networks simultaneously in a time synchronous mode using the clock time measurement system and generate corresponding microseismic data; a computer configured to record said microseismic data of said first and second seismic sensor networks, wherein said computer is programmed to: sum said recorded microseismic data received from the first sensor network over time windows and apply a seismic migration analysis to determine the position of the microseismic events in space using an overburden layer velocity method, and analyze a grid-based volume of migrated seismograms to determine the origin time of the microseismic source; detect, based on said recorded microseismic data time synchronously detected from said second sensor network, compressional P-wave and shear S-wave events, estimate arrival times of microseismic events and perform an auto-search around the estimates to obtain refined origin times of the microseismic events, and determine, using the P-wave and S-wave events, the source location at each origin time of the detected microseismic event; compare the source location and origin determinations from the first and second sensor networks and determine a resultant location and origin time of the microseismic event; and map failure surfaces which define pathways for preferential fluid movement in the reservoir based on the resultant location and origin time determinations; and sum said recorded microseismic data received from the first sensor network over time windows and apply a seismic migration analysis to determine the position of the microseismic events in space using an overburden layer velocity method, and analyze a grid-based volume of migrated seismograms to determine the origin time of the microseismic source; detect, based on said recorded microseismic data time synchronously detected from said second sensor network, compressional P-wave and shear S-wave events, estimate arrival times of microseismic events and perform an auto-search around the estimates to obtain refined origin times of the microseismic events, and determine, using the P-wave and S-wave events, the source location at each origin time of the detected microseismic event; compare the source location and origin determinations from the first and second sensor networks and determine a resultant location and origin time of the microseismic event; and map failure surfaces which define pathways for preferential fluid movement in the reservoir based on the resultant location and origin time determinations; and an output device for displaying a mapping of failure surfaces which define pathways for preferential fluid movement in the reservoir.