Faults in carbonate rocks show both seismic and aseismic deformation processes, leading to a wide range of slip velocities. We deformed two centimeter-scale cores of Carrara marble at 25°C, under in-situ conditions of stress of 2-3 km depth, and imaged the nucleation and growth of creeping faults using dynamic synchrotron X-ray microtomography with micrometer spatial resolution. The first sample was under a constant confinement of 30 MPa and no pore fluid. The second sample was under a confinement in the range 35-23 MPa, with 10 MPa pore fluid pressure. We increased the axial stress by steps until creep deformation occurred and imaged deformation in 4D during creep. The samples deformed with a steady-state strain rate when the differential stress was constant, a process called creep. However, for both samples, we also observed transient events that include the acceleration of creep, i.e., creep bursts, phenomena similar to slow slip events that occur in continental active faults. During these transient creep events, strain rates increase and correlate in time with strain localization and the development of system-spanning fault networks. In both samples, the acceleration of opening and shearing of microfractures accommodated creep bursts. Using high-resolution time-lapse X-ray micro-tomography imaging, and digital image correlation, during triaxial deformation allowed quantifying creep in laboratory faults at sub-grain spatial resolution, and demonstrates that transient creep events (creep bursts) correlate with the nucleation and growth of faults.