The modern seismology took over the classical seismology in 1950s. The former is based on the analysis of individual earthquakes, while the latter took the statistical approach as a whole in understanding earthquakes. The earthquake phenomenon is a good example of fractal, in which the part is as complex as the whole. For understainding this type of complex phenomena, a new view is required other than the reductionist's (modern) view or the wholist's (classical) one. The whole is not a mere sum of the part, due to the nonlinear interaction among the parts. Recent advances in the nonlinear dynamical system theory are clarifying the various effects of nonlinear interactions. Earthquakes are re-examined on this line. In order to explain power-law relations known in seismology, earthquakes are viewed as a self-organized critical phenomenon (SOC). Earthquakes occur as an energy dissipation process in the earth's crust to which the energy is continuously input due to plate tectonics. The crust self-organizes into the critical state and the temporal and spatial fractal structure emerges naturally. Power-law relations are the expression of the critical state of the crust. The SOC model for earthquakes explains the Gutenberg-Richter relation, the Omori's formula of aftershocks and the fractal distribution of hypocenters.