Earthquakes are among the top naturalhazards that cause economic losses. Better understanding earthquake sourceprocesses is important to address fundamental questions in earthquake sourcephysics and hazard reduction. In this presentation, I will combine observationsfrom induced and natural earthquakes to discuss the roles of fluid injection,prior earthquakes, and fault characteristics on earthquake source parameters.Analysis using a dense network in Oklahoma shows that fluid injection causedlow stress drop during fault activation. Result using a high-resolutionborehole network in Parkfield illustrates persistent and stable patterns ofheterogeneity, and temporal changes in earthquake source processes after the2004 M6 earthquake. Global compilation of earthquake source complexity revealssystematic difference at low-deformation and high-deformation regions,suggesting fault characteristics control earthquake rupture patterns.