Which earthquake struck San Francisco on April 18, 1906?

The earthquake that struck San Francisco on April 18, 1906, was the 1906 San Francisco earthquake. It ruptured the northern San Andreas Fault and produced severe shaking across much of coastal northern California.

The main shock began at about 5:12 a.m. local time. Rupture extended for roughly 296 miles, or 477 kilometres, along the fault. Ground movement, collapsed structures, broken water mains, and fires caused widespread destruction in San Francisco and nearby communities. The earthquake’s estimated magnitude is commonly given as about 7.9, though early measurements were not made with modern instruments.

The disaster became a major event in earthquake science. Studies of offset fences and roads helped Harry Fielding Reid formulate elastic rebound theory. The earthquake also encouraged stronger building practices, improved fire response, and systematic fault research.

The fires lasted for several days and destroyed more property than shaking alone in some areas. Modern accounts distinguish the earthquake damage from the later fire damage rather than treating them as one process.