1. A method for processing seismic data, comprising: receiving the seismic data from two sensors in a seismic survey; classifying the seismic data below and equal to a predetermined frequency as low-frequency seismic data; calculating a set of low-frequency Green's functions using interferometry on the low-frequency seismic data; processing high-frequency seismic data of the seismic data to create a set of high-frequency Green's functions at one or more source locations of the seismic survey; merging the set of low-frequency Green's functions and the set of high-frequency Green's functions to create a set of broad-band Green's functions at the source locations; and generating a seismic image using the set of broad-band Green's functions.