Atomic structure and morphology of 6H-SiC(0001) and 3C-SiC(100) surfaces are studied by scanning tunneling microscopy (STM), synchrotron radiation-based !-spot x-ray photoemission spectroscopy (!-spot XPS) and low energy electron microscopy (LEEM). STM shows very high quality Si-rich 6H-SiC(0001) 3x3 surfaces with less than 2% of atomic defects. Si removal upon annealing leads to atomic crack defects formation with a novel 2"3x2"3-R30° reconstruction coexisting with few 3x3 domains having no crack, suggesting important stress relief during the phase transition. LEEM also shows cracks formation on cubic 3C-SiC(100) surfaces and gives insights about surface morphology with large faceting and mesa (!m) formation. These defect fractures developing upon Si removal are likely to be also generated during initial oxidation since the initial oxygen interaction tends to relieve surface strain on SiC in contrast to Si surfaces. These atomic crack defects could be related to the interface electronic states recurrent at SiO2/SiC interfaces.