The basement-involved active fold-thrust belt of the Zagros in southwest Iran is underlain by numerous seismogenic blind basement thrust faults covered by the folded Phanerozoic sedimentary rocks. Meizoseismal regions of moderate- to large-magnitude earthquakes in the Zagros are localized and concentrated along particular structural-geomorphological features and topographic fronts at the surface. The study reveals at least four active SW-vergent segmented master blind thrusts in the Zagros collisional belt, along which different morphotectonic units are thrusting over the deforming regions. These boundary thrusts, which make contiguous frontal asymmetric anticlines, prominent escarpments and Quaternary deformation, mark topographic fronts at the surface, and have vertically displaced geologic marker beds for more than 6000 m, include: the High Zagros (with a maximum recorded historic earthquake of M s = 6.0 at Daryan); the Mountain Front (M s = 7.0 at Khurgu); the Dezful Embayment (M s = 5.7); and the Foredeep (M s = 6.5 at Ahwaz) thrusts. Three other seismogenic blind thrusts responsible for the Qir (M s = 6.9), the Lar (M s = 6.5) and the Beriz-Dehkuyeh (M s = 5.7) earthquakes are also documented in this study. The master faults, as evidenced by deformation of the asymmetric anticlines in the hanging wall of the blind thrusts, are segmented and discontinuous, and are separated by gaps in faulting that have presumably controlled the extent of rupture and the magnitude of earthquakes. The master seismic thrusts are displaced right-laterally by deep-seated active transverse faults of Kazerun (I o = VIII), Sarvestan (M s = 6.4?) and Sabz Pushan. The study shows that active deformation in the Zagros is dominated by: (1) prevalent subsurface blind thrusting; (2) occasional surface strike-slip faulting; (3) coseismic asymmetric folding and uplift of sedimentary cover; and (4) surface thrusting ramping up from at least two regional upper (Miocene Gachsaran) and lower (Lower Cambrian Hormoz) decollement detachments.The active master thrust faults have implications for seismic hazard assessment that were not previously appreciated. The possibility of large compressive earthquakes (M s 7.0) along the introduced blind thrusts must be considered. Locations of other unknown segmented blind thrusts in the belt, which have distinct effects on the surface morphotectonics and topography, and on the structures at depth, could be easily based on meizoseismal maps of the earthquakes combined with active morphotectonic features, morphometric analyses and accurate aftershock sequence studies.