At 05:12 AM Pacific Standard Time on Wednesday, April 18, 1906, the coast of Northern California was struck by a major earthquake with an estimated moment magnitude of 7.9 and a maximum Mercalli intensity of XI (Extreme).

High-intensity shaking was felt from Eureka on the North Coast to the Salinas Valley, an agricultural region to the south of the San Francisco Bay Area.

Accumulated strain on the faults in the system was relieved during the earthquake, which is the supposed cause of the damage along the 280-mile-long (450 km) segment of the San Andreas plate boundary.

[11] For years, the epicenter of the quake was assumed to be near the town of Olema, in the Point Reyes area of Marin County, due to local earth displacement measurements.

The available seismological data support a significantly shorter rupture length, but these observations can be reconciled by allowing propagation at speeds above the S-wave velocity (supershear).

Though San Francisco rebuilt quickly, the disaster diverted trade, industry, and population growth south to Los Angeles,[citation needed] which during the 20th century became the largest and most important urban area in the West.

Many of the city's leading poets and writers retreated to Carmel-by-the-Sea where, as "The Barness", they established the arts colony reputation that continues today.

[23] The earthquake was the first natural disaster of its magnitude to be documented by photography and motion picture footage and occurred at a time when the science of seismology was blossoming.

The city's fire chief, Dennis T. Sullivan, who would have been responsible for coordinating firefighting efforts, had died from injuries sustained in the initial quake.

[44] One landmark building lost in the fire was the Palace Hotel, subsequently rebuilt, which had many famous visitors including royalty and celebrated performers.

The night after Caruso's performance in Carmen, the tenor was awakened in the early morning in his Palace Hotel suite by a strong jolt.

Clutching an autographed photo of President Theodore Roosevelt, Caruso made an effort to get out of the city, first by boat and then by train, and vowed never to return to San Francisco.

[50] The interim fire chief sent an urgent request to the Presidio, a United States Army post on the edge of the stricken city, for dynamite.

Telephoning a San Francisco Police Department officer, he sent word to Mayor Eugene Schmitz of his decision to assist and then ordered federal troops from nearby Angel Island to mobilize and enter the city.

[citation needed] During the first few days, soldiers provided valuable services like patrolling streets to discourage looting and guarding buildings such as the U.S. Mint, post office, and county jail.

Police officers, firefighters, and soldiers would regularly commandeer passing civilians for work details to remove rubble and assist in rescues.

Ord later wrote a long letter[53] to his mother on April 20 regarding Schmitz's "Shoot-to-Kill" order and some "despicable" behavior of certain soldiers of the 22nd Infantry who were looting.

[54][55] Political and business leaders strongly downplayed the effects of the earthquake, fearing loss of outside investment in the city which was badly needed to rebuild.

[56] In his first public statement, California Governor George Pardee emphasized the need to rebuild quickly: "This is not the first time that San Francisco has been destroyed by fire, I have not the slightest doubt that the City by the Golden Gate will be speedily rebuilt, and will, almost before we know it, resume her former great activity".

Rebuilding funds were immediately tied up by the fact that virtually all the major banks had been sites of the conflagration, requiring a lengthy wait of seven to ten days before their fire-proof vaults could cool sufficiently to be safely opened.

Its president also immediately chartered and financed the sending of two ships to return with shiploads of lumber from Washington and Oregon mills which provided the initial reconstruction materials and surge.

[61] William James, the pioneering American psychologist, was teaching at Stanford at the time of the earthquake and traveled into San Francisco to observe first-hand its aftermath.

Following the 1906 San Francisco earthquake, more than 40,000 people were relocated to a makeshift tent city in Golden Gate Park and were treated by the faculty of the Affiliated Colleges.

[65] The grandeur of citywide reconstruction schemes required investment from Eastern monetary sources, hence the spin and de-emphasis of the earthquake, the promulgation of the tough new building codes, and subsequent reputation sensitive actions such as the official low death toll.

The houses were designed by John McLaren, and were grouped in eleven camps, packed close to each other and rented to people for two dollars per month until rebuilding was completed.

Also, aside from merely expanding nonresidential uses in many neighborhoods, the fire created economic opportunities in new areas, resulting in clusters of business activity that emerged only in the wake of the disaster.

[70] These relief efforts were not enough to get families on their feet again, and consequently the burden was placed on wealthier members of the city, who were reluctant to assist in the rebuilding of homes they were not responsible for.

Award presentations, religious services, a National Geographic TV movie,[87] a projection of fire onto the Coit Tower,[88] memorials, and lectures were part of the commemorations.

The USGS Earthquake Hazards Program issued a series of Internet documents,[89] and the tourism industry promoted the 100th anniversary as well.

William Del Monte, then 103, and Jeanette Scola Trapani (1902–2009),[94] 106, stated that they stopped attending events commemorating the earthquake when it became too much trouble for them.