Solar activity, as indicated by sunspots, radio noise and geomagnetic indices, plays a significant but by no means exclusive role in the triggering of earthquakes. Maximum quake frequency occurs at times of moderately high and fluctuating solar activity. Terrestrial solar flare effects which are the actual coupling mechanisms which trigger quakes appear to be either abrupt accelerations in the earth's angular velocity or surges of telluric currents in the earth's crust. The graphs presented in this paper permit probabilistic forecasting of earthquakes, and when used in conjunction with local indicators may provide a significant tool for specific earthquake prediction.