We describe new evidence of Quaternary faulting observable in large outcrop exposures (trenches and carries) near Romilly-sur-Seine in the centre of Paris basin. Coeval normal or reverse faults affect sand, marl and gravel units that also expose liquefaction features. Quaternary units with thicknesses ranging from decimetre to metre are sealed by non-deformed deposits. The coexistence of soft and brittle tectonics with ~1 m vertical offset in a single cross-section, affecting different stratigraphic levels, reflects their diachronic nature and attest for their coseismic origin. The faulting of young deposits visible in the paleoseismic sites belong to the major regional tectonic structures, i.e. the Omey and Vittel fault system that affects the late Quaternary units of the east Paris basin. Their activity known locally as Ypresian polyphased seismites, seems to have continued until the late Quaternary. The Quaternary ruptures and coseismic nature of the fault system call for a realistic seismic hazard assessment in this intraplate tectonic environment.