Checking the validity of a subsurface starting model for performing full waveform inversion on seismic data

There is provided a method for checking the validity of a geophysical representation of a portion of the volume of the Earth generated from a seismic measurement. The method comprises obtaining 100 a measured phase data set derived from a measured seismic data set and a modelled phase data set 104 generated from a subsurface starting model. Different aspects of the invention relate to different methods of using these data sets to determine the validity of the starting model for performing full waveform inversion on the measured seismic data set. For example, in one aspect, the correlation between the spatial location of one or more phase distribution features within a measured phase distribution data set and the spatial location of one or more corresponding phase distribution features within a modelled phase data set is analysed. Another aspect relates to a method for subsurface exploration.