1. A computer-implemented method for estimating a physical properties model in a subsurface region using data comprising two or more geophysical data types, said model comprising numbers in a model parameter domain representing one or more physical properties, said method comprising: using a computer to jointly invert the data in a plurality of sequential phases, wherein in each phase until a last phase, only a portion of the data is inverted in order to infer a subset of the model's parameter domain, said portion being determined at least partly based on relative frequency content of the two or more data types.