The correlation between compositional modulations and surface morphology has been studied by transmission electron microscopy (TEM) and atomic force microscopy (AFM) fora series of tensile strained In1-xGaxAsyP1-y films grown by molecular beam epitaxy (MBE) on (100) InP substrates. At low values of strain (0.6%), both a quaternary In0.65Ga0.35As0.6P0.4 film and ternary In0.45Ga0.55As film show anisotropic behavior (both with regards to composition modulation and surface morphology) between [011] and [0 (1) over bar1] cross-sections. The composition modulation and surface undulation are prominent only in the [0 (1) over bar1] cross-section. The In0.45Ga0.55As films develop a coarse faceted structure on (411) and (4 (1) over bar1) planes after similar to 100 nm of film growth. Composition modulations (scaling with the size of the facets) are observed in films 0.1-1 mum thick, but in thicker films ( > 1 mum) the faceted structure disappears while the scale of the compositional modulations decays to that found in unstrained films. On the other hand 2% tensile strained In0.25Ga0.75As and In0.72Ga0.28P films show pronounced faceting with no evidence for compositional modulations, and ;2% tensile strained In0.5Ga0.5As0.5P0.5 films show composition modulation without scaling and no faceted surface. The results are discussed in terms of the interplay between thermodynamic driving force, leading to segregation and faceting, and kinetic factors.