The 1906 San Francisco Earthquake and Fires
At 5:12 a.m. on 18 April, a magnitude 7.8 earthquake ruptured hundreds of kilometers of the San Andreas Fault. Severe shaking damaged communities across northern California. In San Francisco, broken water mains, damaged gas systems, and hundreds of fires turned the earthquake into a multi-day urban disaster.
- When
- 18–21 April 1906Date range
- Where
- San Francisco and the San Andreas Fault rupture zoneUnited States · General area
- Evidence
- VerifiedSources reviewed below
- Sensitivity
- Highly sensitive subjectPresented with care
The place
Before
What existed before
San Francisco had expanded rapidly after the Gold Rush. Dense development, varied construction quality, and infrastructure crossing active faults created interconnected risks that were poorly understood by the public and only partly addressed by engineering practice.
Cause
Trigger and conditions
The Pacific and North American plates slipped along the San Andreas Fault. The rupture propagated for roughly 300 miles. Shaking collapsed buildings and damaged utilities; with much of the water system disabled, firefighting became exceptionally difficult.
Sequence
Timeline
Mainshock
A magnitude 7.8 earthquake begins offshore and ruptures the San Andreas Fault.
Fires spread
Damaged utilities and limited water allow fires to consume much of central San Francisco.
Scientific commission reports
Investigators begin documenting fault displacement, shaking, and structural damage.
Lawson Report published
The comprehensive report becomes a foundation for modern earthquake science.
After
Aftermath
Large parts of the city burned, thousands died, and approximately 225,000 people were left homeless. Residents formed camps, relief systems distributed food and water, and rebuilding began amid contested decisions about land, housing, and whose losses were recorded.
Long-term consequences
The post-earthquake investigation produced the Lawson Report, a landmark scientific record. Evidence from 1906 contributed to elastic-rebound theory, modern fault science, hazard mapping, and continuing changes in seismic engineering and emergency planning.
Significance
The essential question
Why this still matters
The disaster remains a powerful example of cascading risk: a geologic event became an urban fire and housing emergency because critical systems failed together. Data gathered immediately afterward still support earthquake research.
What remains today
The fault trace is visible at sites across the Bay Area. Surviving buildings, rebuilt neighborhoods, refugee-camp records, photographs, and high-water infrastructure planning connect the modern city to 1906.
Evidence
Sources
Sources support specific claims; inclusion does not imply that every source is equally authoritative on every question.
- 01The 1906 earthquake and a century of progress in understanding earthquakes and their hazards
U.S. Geological Survey
USGS synthesis of losses, the investigation, and the event’s scientific legacy.Open source - 02Facing the Great Disaster
U.S. Geological Survey
Detailed account of shaking, fault rupture, fires, and the USGS response.Open source