San Francisco Earthquake

In the early morning of April 18, 1906, a powerful earthquake struck the northern California coast, rupturing the San Andreas Fault and devastating San Francisco. The shaking itself caused serious damage, but the fires that followed destroyed much more of the city. Estimates of the death toll have risen over the years, and modern historians generally believe that more than 3,000 people died, making it one of the deadliest natural disasters in United States history. It also became a landmark event in the science of earthquakes.

San Francisco had grown rapidly since the Gold Rush of 1849 and was the largest city on the West Coast, a major port and financial center. Much of it was built quickly, often on filled land along the waterfront and on former marshes, where the ground was especially prone to shaking. Many buildings were wood-framed, and the city had a history of destructive fires. Its water supply depended on mains that crossed fault-prone terrain, a vulnerability that would prove costly.

The quake struck shortly after 5:00 a.m. and lasted less than a minute, though it was felt across a wide area of California and Nevada. The fault ruptured along roughly 300 miles, by modern estimates. Brick buildings collapsed, streets buckled, and gas lines and chimneys set off numerous fires. With water mains broken, firefighters had little to work with, and the fire chief had been fatally injured in the collapse of his quarters. Fires burned for several days, and authorities used dynamite to create firebreaks, with mixed results and some fires started by the blasting itself. By the end, a large share of the city, including most of downtown, lay in ruins, and several hundred thousand residents were left homeless. Many took shelter in parks and camps run by the army.

Rebuilding began almost immediately, and the city was largely reconstructed within a few years, staging the Panama-Pacific International Exposition in 1915 partly to showcase its recovery. Officials and business leaders often downplayed the role of the earthquake, emphasizing the fire instead, since fire damage was more likely to be covered by insurance and less likely to scare off investors. As a result, early casualty figures were probably undercounted, and Chinese residents and the poor were especially likely to be overlooked in records.

Scientifically, the disaster was a turning point. A state commission led by geologist Andrew Lawson produced a detailed report on the event and identified the San Andreas Fault as a major feature. Studies of the fault's movement helped geologist Harry Fielding Reid develop the elastic rebound theory, which explains how strain builds up and is suddenly released in earthquakes. That theory remains central to seismology and to building codes that now shape construction in earthquake country.