__1906: __San Francisco is destroyed by an earthquake so powerful that it is felt from Coos Bay, Oregon, to Los Angeles, and as far east as central Nevada.

What became known as the San Francisco earthquake and fire struck at 5:12 a.m., when the San Andreas Fault gave way, tearing the earth wide open from Humboldt County, near the Oregon border, to San Benito County, a hundred miles southeast of San Francisco. The epicenter was on the fault line just offshore from the San Francisco-San Mateo county line.

The earthquake had a magnitude measuring anywhere from 7.8 to 8.3 � a precise method of measuring seismic activity did not exist in 1906 � but it was enormous by any standard. There have been larger earthquakes recorded in California, but none so near a major population center. And damage was widespread all along the fault line. The town of Santa Rosa, 50 miles north of the Golden Gate, was flattened. Stanford University, in what was later to be named Silicon Valley, suffered severe damage.

But turn-of-the-century San Francisco was, by far, the most populous and important city in California � it was the cultural and financial hub of the entire West Coast, in fact � and almost all the attention was focused on the carnage there.

Even without the fire that followed, the damage was severe. The earthquake kept shaking for a full minute. By the time it subsided, a number of buildings in town had collapsed. Brick buildings with foundations of unreinforced masonry, especially those standing on land fill, proved especially vulnerable.

But the quake also ruptured gas and water mains, causing fires to break out and leaving the fire department with no water to fight them. San Francisco, then as now a tightly compact city with a lot of wooden structures, burned well.

The result was a conflagration lasting nearly four days. To stop the great fire, mansions lining the broad thoroughfare of Van Ness Avenue were dynamited by Army engineers to create a firebreak by robbing the flames of something to burn. By the time it was over the heart of San Francisco lay in ruins. In all, 508 city blocks had burned to the ground.

Anywhere from 3,000 to 5,000 people were killed, most of them as a result of the earthquake itself, making this one of the biggest natural disasters in U.S. history.

A new city emerged quickly (a little too quickly, some historians would say) on the ashes of the old. Also emerging was a new emphasis on seismological studies and new regulations regarding building construction. In order to guarantee a water supply in the event of another major fire, San Francisco constructed a network of reservoirs, underground cisterns, fireboats and sea-water pumps.

San Francisco today also has some of the toughest building codes on earth – and yet remains vulnerable to both earthquake and fire. In San Francisco, it's not a question of whether the next big one is coming, only of when.

(Source: Bancroft Library)