San Francisco is very close to a fault, or a place where 2 tectonic plates meet and push against each other. When these plates shift it causes seismic activity, or strong waves of force. These waves of force are so strong that they move and shake the earth, these are called tremors, and they turn are what you feel during an earthquake. When more shakes are felt, the energy released is called an aftershock. What caused the San Francisco earthquake was the shifting of tectonic plates. I hope I helped you learn! brainliest would be much appreciated!!
