Source time is a kinematic fault parameter corresponding to the duration of seismic source time functions and is accurately determined from phase spectra of long-period surface waves. Source times are determined for 36 large earthquakes during the last three decades. Scaling relations among source times, seismic moments, and fault dimensions are derived. Seismic moment is proportional to the cube of source time, and fault dimension is proportional to source time. Source times for low-angle thrust earthquakes along deep-sea trenches are found to be longer than those of other types, such as intraplate shocks and deep shocks. They are also significantly longer than the rupture times expected from a Haskell model, suggesting that, generally, there exists an introductory stage of faulting that precedes the main stage of the rupture propagation.