The Great San Francisco Earthquake occurred in 1906. Its main shock struck Northern California on April 18, rupturing a long section of the San Andreas Fault and producing severe shaking across the region.
The earthquake is commonly estimated at about magnitude 7.9, although early twentieth-century instruments and later analyses have produced slightly different estimates. The rupture began offshore near San Francisco, and strong shaking lasted roughly 45 to 60 seconds in the Bay Area.
The disaster is especially remembered for the fires that followed the earthquake. Broken water mains, damaged buildings, and disrupted firefighting made the fires difficult to control, leaving much of San Francisco in ruins. The event also became a turning point in earthquake science because investigations of the fault rupture helped establish the relationship between earthquakes and movement along faults. It is sometimes confused with the 1989 Loma Prieta earthquake, another major Northern California event.