Patent ID: 8077546

Claim:
A method for monitoring a multi-layered system in a subsurface formation that includes a slow layer and a fast layer; the method comprising: a) providing a set of signals obtained by: i) transmitting one or more seismic waves from one or more seismic sources through the multi-layered system; and ii) receiving signals emanating from the multi-layered system in response to the one or more seismic waves with one or more receivers located a distance from the one or more seismic sources; wherein at least one of said seismic sources and receivers is in a well; b) identifying among the received signals at least one critically refracted compressional (CRC) wave that has traveled along an interface between the fast layer and an adjacent layer; c) performing steps a) and b) in a time-lapse mode so as to obtain at least two CRC waves; d) inferring information about a change in the slow layer based on the at least two CRC waves; and e) imaging the information from step d).