Great San Francisco Earthquake

At 05:12 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. Devastating fires soon broke out in San Francisco and lasted for several days. More than 3,000 people died, and over 80% of the city was destroyed. The events are remembered as one of the worst and deadliest earthquakes in the history of the United States. The death toll remains the greatest loss of life from a natural disaster in California's history and high on the lists of American disasters.

Tectonic setting

The San Andreas Fault is a continental transform fault that forms part of the tectonic boundary between the Pacific Plate and the North American Plate. The strike-slip fault is characterized by mainly lateral motion in a dextral sense, where the western (Pacific) plate moves northward relative to the eastern (North American) plate. This fault runs the length of California from the Salton Sea in the south to Cape Mendocino in the north, a distance of about . The maximum observed surface displacement was about 20 feet (6 m); geodetic measurements show displacements of up to 28 feet (8.5 m).

Earthquake

The 1906 earthquake preceded the development of the Richter magnitude scale by three decades. The most widely accepted estimate for the magnitude of the quake on the modern moment magnitude scale is 7.9; values from 7.7 to as high as 8.3 have been proposed. According to findings published in the ''Journal of Geophysical Research'', severe deformations in the Earth's crust took place both before and after the earthquake's impact. Accumulated strain on the faults in the system was relieved during the earthquake, which is the supposed cause of the damage along the segment of the San Andreas plate boundary. The 1906 rupture propagated both northward and southward for a total of . Shaking was felt from Oregon to Los Angeles, and as far inland as central Nevada.Christine Gibson
"Our 10 Greatest Natural Disasters," ''American Heritage'', Aug./Sept. 2006.

A strong foreshock preceded the main shock by about 20 to 25 seconds. The strong shaking of the main shock lasted about 42 seconds. There were decades of minor earthquakes – more than at any other time in the historical record for northern California – before the 1906 quake. Previously interpreted as precursory activity to the 1906 earthquake, they have been found to have a strong seasonal pattern and are now believed to be caused by large seasonal sediment loads in coastal bays that overlie faults as a result of the erosion caused by hydraulic mining in the later years of the California Gold Rush.

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. In the 1960s, a seismologist at UC Berkeley proposed that the epicenter was more likely offshore of San Francisco, to the northwest of the Golden Gate. The most recent analyses support an offshore location for the epicenter, although significant uncertainty remains. An offshore epicenter is supported by the occurrence of a local tsunami recorded by a tide gauge at the San Francisco Presidio; the wave had an amplitude of approximately and an approximate period of 4045 minutes.

Analysis of triangulation data before and after the earthquake strongly suggests that the rupture along the San Andreas Fault was about in length, in agreement with observed intensity data. 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). Supershear propagation has now been recognized for many earthquakes associated with strike-slip faulting.

Recently, using old photographs and eyewitness accounts, researchers were able to estimate the location of the hypocenter of the earthquake as offshore from San Francisco or near San Juan Bautista, confirming previous estimates.

Intensity

The most important characteristic of the shaking intensity noted in Andrew Lawson's 1908 report was the clear correlation of intensity with underlying geologic conditions. Areas situated in sediment-filled valleys sustained stronger shaking than nearby bedrock sites, and the strongest shaking occurred in areas of former bay where soil liquefaction had occurred. Modern seismic-zonation practice accounts for the differences in seismic hazard posed by varying geologic conditions. The shaking intensity as described on the Modified Mercalli intensity scale reached XI (''Extreme'') in San Francisco and areas to the north like Santa Rosa where destruction was devastating.

Aftershocks

The main shock was followed by many aftershocks and some remotely triggered events. As with the 1857 Fort Tejon earthquake, there were fewer aftershocks than would have been expected for a shock of that size. Very few of them were located along the trace of the 1906 rupture, tending to concentrate near the ends of the rupture or on other structures away from the San Andreas Fault, such as the Hayward Fault. The only aftershock in the first few days of near M 5 or greater occurred near Santa Cruz at 14:28 PST on April 18, with a magnitude of about 4.9 . The largest aftershock happened at 01:10 PST on April 23, west of Eureka with an estimated magnitude of about 6.7 , with another of the same size more than three years later at 22:45 PST on October 28 near Cape Mendocino.

Remotely triggered events included an earthquake swarm in the Imperial Valley area, which culminated in an earthquake of about 6.1 at 16:30 PST on April 18, 1906. Another event of this type occurred at 12:31 PST on April 19, 1906, with an estimated magnitude of about 5.0 , and an epicenter beneath Santa Monica Bay.

Damage

Early death counts ranged from 375 to over 500. However, hundreds of fatalities in Chinatown went ignored and unrecorded. The total number of deaths is still uncertain, but various reports presented a range of 700–3,000+. In 2005, the city's Board of Supervisors voted unanimously in support of a resolution written by novelist James Dalessandro ("1906") and city historian Gladys Hansen ("Denial of Disaster") to recognize the figure of 3,000 plus as the official total. Most of the deaths occurred within San Francisco, but 189 were reported elsewhere in the Bay Area; nearby cities such as Santa Rosa and San Jose also suffered severe damage. In Monterey County, the earthquake permanently shifted the course of the Salinas River near its mouth. Where previously the river emptied into Monterey Bay between Moss Landing and Watsonville, it was diverted south to a new channel just north of Marina.

Between 227,000 and 300,000 people were left homeless out of a population of about 410,000; half of those who evacuated fled across the bay to Oakland and Berkeley. Newspapers described Golden Gate Park, the Presidio, the Panhandle and the beaches between Ingleside and North Beach as covered with makeshift tents. More than two years later, many of these refugee camps were still in operation.

The earthquake and fire left long-standing and significant pressures on the development of California. At the time of the disaster, San Francisco had been the ninth-largest city in the United States and the largest on the West Coast. Over a period of 60 years, the city had become the financial, trade, and cultural center of the West, operating the busiest port on the West Coast. It was the "gateway to the Pacific", through which growing U.S. economic and military power was projected into the Pacific and Asia. Over 80% of the city was destroyed by the earthquake and fire. Though San Francisco rebuilt quickly, the disaster diverted trade, industry, and population growth south to Los Angeles, 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.

The 1908 Lawson Report, a study of the 1906 quake led and edited by Professor Andrew Lawson of the University of California, showed that the same San Andreas Fault which had caused the disaster in San Francisco ran close to Los Angeles as well. 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.

Other cities

Although the impact of the earthquake on San Francisco was the most famous, the earthquake also inflicted considerable damage on several other cities. These include San Jose and Santa Rosa, the entire downtown of which was essentially destroyed.

Fires

As damaging as the earthquake and its aftershocks were, the fires that burned out of control afterward were even more destructive. It has been estimated that up to 90% of the total destruction was the result of the subsequent fires. Within three days, over 30 fires, caused by ruptured gas mains, destroyed approximately 25,000 buildings on 490 city blocks. The fires cost an estimated $350 million at the time (equivalent to $ billion in ).

Some of the fires were started when San Francisco Fire Department firefighters, untrained in the use of dynamite, attempted to demolish buildings to create firebreaks. The dynamited buildings often caught fire. 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. In total, the fires burned for four days and nights.

Most of the destruction in the city was attributed to the fires, since widespread practice by insurers was to indemnify San Francisco properties from fire but not from earthquake damage. Some property owners deliberately set fire to damaged properties to claim them on their insurance. Captain Leonard D. Wildman of the U.S. Army Signal Corps reported that he "was stopped by a fireman who told me that people in that neighborhood were firing their houses...they were told that they would not get their insurance on buildings damaged by the earthquake unless they were damaged by fire".

One landmark building lost in the fire was the Palace Hotel, subsequently rebuilt, which had many famous visitors including royalty and celebrated performers. It was constructed in 1875 primarily financed by Bank of California co-founder William Ralston, the "man who built San Francisco". In April 1906, the tenor Enrico Caruso and members of the Metropolitan Opera Company came to San Francisco to give a series of performances at the Grand Opera House. 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. Caruso died in 1921, having remained true to his word. The Metropolitan Opera Company lost all of its traveling sets and costumes in the earthquake and ensuing fires.

Some of the greatest losses from fire were in scientific laboratories. Alice Eastwood, the curator of botany at the California Academy of Sciences in San Francisco, is credited with saving nearly 1,500 specimens, including the entire type specimen collection for a newly discovered and extremely rare species, before the remainder of the largest botanical collection in the western United States was destroyed in the fire. The entire laboratory and all the records of Benjamin R. Jacobs, a biochemist who was researching the nutrition of everyday foods, were destroyed. The original California flag used in the 1846 Bear Flag Revolt at Sonoma, which at the time was being stored in a state building in San Francisco, was also destroyed in the fire.

Response

The city's fire chief, Dennis T. Sullivan, was gravely injured when the earthquake first struck and later died from his injuries. 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. General Frederick Funston had already decided that the situation required the use of federal troops. 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. Explosives were ferried across the bay from the California Powder Works in what is now Hercules.

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. They aided the fire department in dynamiting to demolish buildings in the path of the fires. The Army also became responsible for feeding, sheltering, and clothing the tens of thousands of displaced residents of the city. Under the command of Funston's superior, Major General Adolphus Greely, Commanding Officer of the Pacific Division, over 4,000 federal troops saw service during the emergency. Police officers, firefighters, and soldiers would regularly commandeer passing civilians for work details to remove rubble and assist in rescues. On July 1, 1906, non-military authorities assumed responsibility for relief efforts, and the Army withdrew from the city.

On April 18, in response to riots among evacuees and looting, Mayor Schmitz issued and ordered posted a proclamation that "The Federal Troops, the members of the Regular Police Force and all Special Police Officers have been authorized by me to kill any and all persons found engaged in Looting or in the Commission of Any Other Crime". Accusations of soldiers engaging in looting also surfaced. Retired Captain Edward Ord of the 22nd Infantry Regiment was appointed a special police officer by Schmitz and liaised with Greely for relief work with the 22nd Infantry and other military units involved in the emergency. Ord later wrote a long letter 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. He also made it clear that the majority of soldiers served the community well.

Aftermath

Property losses from the disaster have been estimated to be more than $400 million in 1906 dollars. This is equivalent to $ in dollars. An insurance industry source tallies insured losses at $235 million, the equivalent to $ in dollars.

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. 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". The earthquake is not even mentioned in the statement. Fatality and monetary damage estimates were manipulated.

Almost immediately after the quake (and even during the disaster), planning and reconstruction plans were hatched to quickly rebuild the city. 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. The Bank of Italy (now Bank of America) had evacuated its funds and was able to provide liquidity in the immediate aftermath. 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. Eleven days after the earthquake a rare Sunday baseball game was played in New York City (which would not allow regular Sunday baseball until 1919) between the Highlanders (soon to be the Yankees) and the Philadelphia Athletics to raise money for quake survivors.

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. He was most impressed by the positive attitude of the survivors and the speed with which they improvised services and created order out of chaos. This formed the basis of the chapter "On some Mental Effects of the Earthquake" in his book ''Memories and Studies''.

H. G. Wells

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