On April 18, 1906, a 7.9 magnitude earthquake along the San Andreas Fault would reshape the entire city.
The great San Francisco earthquake struck on Wednesday, April 18, 1906 at 5:12 am, with the offshore epicenter about 3 km (2 mi) south of the city. It ruptured 477 km (296 mi) along the San Andreas Fault. People felt shaking from Oregon in the Pacific Northwest to Los Angeles and from the inland to central Nevada. Its magnitude is estimated at 7.9, but values up to 8.25 have been proposed. The quake and resulting fire were one of the worst natural disasters in California. The death toll is estimated at over 3,000 people. After the earthquake, about 200,000 people were left homeless. Thousands camped at city parks in tents supplied by the Army.
At the time of the Great San Francisco Earthquake, instruments to measure earthquakes were non-existent in the area. Therefore, scientists who measure earthquakes that happened before 1900 review historical accounts of damage to buildings, the distance at which people felt tremors from the epicenter, and reports on changes in the soil. From this information they try to determine the intensity and magnitude of the earthquakes.