A method for processing seismic data. The method includes receiving the seismic data acquired by at least two receivers that are disposed at different depths. The method may then time-align the seismic data, collect a portion of the time-aligned seismic data into a gather and sum the collected time-aligned seismic data in the gather. After summing the collected time-aligned seismic data in the gather, the method may widen a spectrum of the summed seismic data and generate an image of subsurface formations in the earth based on the widened spectrum.