Periodic self-organization of matter beyond the diffraction limit is a puzzling phenomenon, typical both for surface and bulk ultrashort laser processing. Here we compare the mechanisms of periodic nanostructure formation on the surface and in the bulk of fused silica. We show that volume nanogratings and surface nanoripples having subwavelength periodicity and oriented perpendicular to the laser polarization share the same electromagnetic origin. The nanostructure orientation is defined by the near-field local enhancement in the vicinity of the inhomogeneous scattering centers. The periodicity is attributed to the coherent superposition of the waves scattered at inhomogeneities. Numerical calculations also support the multipulse accumulation nature of nanogratings formation on the surface and inside fused silica. Laser surface processing by multiple laser pulses promotes the transition from the high spatial frequency perpendicularly oriented nanoripples to the low spatial frequency ripples, parallel or perpendicular to the laser polarization. The latter structures also share the electromagnetic origin, but are related to the incident field interference with the scattered far-field of rough non-metallic or transiently metallic surfaces. The characteristic ripple appearances are predicted by combined electromagnetic and thermo-mechanical approaches and supported by SEM images of the final surface morphology and by time-resolved pump-probe diffraction measurements. The ability to inscribe periodic nanostructures on the surface and in the bulk of dielectrics by ultrafast laser irradiation has been a subject of increasing interest and active investigation during few last decades 1. Not surprisingly, the polarization-dependent, rewritable and the smallest structures ever created by light are promising in optical data storage, security color marking, tribology, nanofluidics and computer holography 1–4. Although the mechanisms of their formation are controversially discussed and are not clearly distinguished 1,5–7 , there is a strong experimental evidence of the electromagnetic nature of the phenomena due to local field polarization, incident angle dependency of the nanostructure orientation 3,8–11 , and laser wavelength dependency of the nanostructure periodicity 1,12. The key role of inhomogeneous scattering centers attributed to initial surface nanoroughness, laser-induced defects, pre-distributed grooves, nanovoids or nanopores in case of bulk nanostructuring was also evidenced in experiments 7,13–18 and proven numerically 19–23. In spite of the fact that laser-induced periodic surface structures (LIPSS) and volume nanogratings have many characteristics in common, both are often attributed to different phenomena, taking place close to surface or deep in the bulk of the material 5. On one hand, volume nanogratings have striking similarities with femtosecond high spatial frequency LIPSS (HSFL), sharing sub-wavelength periodicity as well as laser polarization and laser