1906 SAN FRANCISCO EARTHQUAKE

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1906 SAN FRANCISCO EARTHQUAKE

• 512 am on April 18, 1906
• Fires lasting for 3 days
• 490 blocks destroyed
• 25,000 buildings toppled
• Gas and water lines ruptured
• Loss of electric power

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1906 San Francisco Earthquake

• William Alexander Coulters (1849-1936) panorama
  of the largest maritime rescue in United States
  history. The painting depicts the fleet of
  rescue vessels that ferried more than 30,000
  people to safety from the burning city.

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Earthquake Science Before After 1906

• Earthquake research in the U.S. had advanced
  slowly compared to efforts in Japan and Europe.
• Only a small number of geology professors at U.S.
  universities and USGS geologists studied
  earthquakes.
• Little was known about how and where they
  occurred, and the hazards they presented.
• Theory of plate tectonics was still more than a
  half-century away.
• 1906 Earthquake started the study of earthquakes
  and California geology in earnest.
• State Earthquake Investigation Commission is
  formed Andrew C. Lawson.
• 1908 Lawson report was released.

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San Andreas Fault
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San Andreas Fault

• Amount and Rate of offset variable.
• Consists of a complex system of parallel and
  interconnecting faults.

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April 18, 1906

• 512 AM Initial foreshock
• 20-25 seconds later The great earthquake hits.
• Strong shaking lasted 45-60 seconds.
• Rupture length 290 miles.

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Magnitude Intensity

• 1906 Earthquake magnitude was 7.8. Traditional
  estimates went as high as 8.3, whereas modern
  estimates range from 7.7 to 7.9.
• Shaking intensities of VIII (moderate damage) to
  IX (heavy damage) extended as much as 60 miles
  inland along a broad band paralleling the fault
  trace depending on the softness of the
  subsurface materials.

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Seismograms

• Time advances from left to right. Small wiggles,
  beginning 1/2 inch from left end, signal arrival
  of first compressional (P) waves. Large wiggles
  half way along represent arrival of
  slower-traveling shear (S) waves.

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Predictive Intensity Map
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1906 Earthquake Offset
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1906 Earthquake Offset
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The City of San Francisco

• All of a sudden we had found ourselves
  staggering and reeling. It was as if the earth
  was slipping gently from under our feet. Then
  came the sickening swaying of the earth that
  threw us flat upon our faces. We struggled in the
  street. We could not get on our feet. Then it
  seemed as though my head were split with the roar
  that crashed into my ears. Big buildings were
  crumbling as one might crush a biscuit in one's
  hand. Ahead of me a great cornice crushed a man
  as if he were a maggot - a laborer in overalls on
  his way to the Union Iron Works with a dinner
  pail on his arm. (P. Barrett).

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The City of San Francisco

• The air was filled with falling stones. People
  around me were crushed to death on all sides. All
  around the huge buildings were shaking and waving.

We rushed down Market Street. Men, women and
children were crawling from the debris. Hundreds
were rushing down the street and every minute
people were felled by debris.(G.A. Raymond)
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The City of San Francisco

• When the fire caught the Windsor Hotel at Fifth
  and Market Streets there were three men on the
  roof, and it was impossible to get them down.
  Rather than see the crazed men fall in with the
  roof and be roasted alive the military officer
  directed his men to shoot them, which they did in
  the presence of 5,000 people. (Max Fast).

The most terrible thing I saw was the futile
struggle of a policeman and others to rescue a
man who was pinned down in burning wreckage. The
helpless man watched it in silence till the fire
began burning his feet. Then he screamed and
begged to be killed. The policeman took his name
and address and shot him through the head.
(Adolphus Busch).
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The City of San Francisco

• The street car tracks were bent and twisted out
  of shape. Electric wires lay in every direction.
  Streets on all sides were filled with brick and
  mortar, buildings either completely collapsed or
  brick fronts had just dropped completely off.
  Wagons with horses hitched to them, drivers and
  all, lying on the streets, all dead., struck and
  killed by the falling bricks.

The water mains had been broken by the
earthquake, and so there was no supply for the
fire engines and they were helpless. The only way
out was to dynamite, and I saw some of the finest
and most beautiful buildings in the city, new
modern palaces, blown to atoms. (Jerome B. Clark)
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The City of San Francisco

• Fire destroyed 2,831 acres of the city more
  than 490 blocks.
• 30 schools, 80 churches, and 250,000 homes were
  destroyed.
• Modern estimates of at least 3000 people were
  killed.
• Roughly 225,000 people were left homeless from a
  population of about 400,000.
• Estimated property damage of 400,000,000 in 1906
  dollars.

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The City of San Francisco
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Aftermath

• The San Francisco Daily News was the only
  newspaper to publish on April 18.The Daily
  News plant, downtown, lost power and water in
  the earthquake, and moved to J.V. Rooneys small
  printing shop at 1308 Mission Street, where this
  edition was turned out on a hand-cranked press
  capable of printing single sheets. New editions
  were printed until the shop was ordered evacuated
  because it was to be dynamited.

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Aftermath
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Propaganda and Corruption

• Railroads controlled California politics at the
  time.
• Southern Pacific Railroad Co. was aggressive in
  its attempt to rewrite the history of the
  earthquake.
• Sunset magazine was devoted to extolling the
  wonders of California and was a promotion tool
  for the railroad.
• Propoganda articles stressed the rebuilding of
  the city and highlighted the damage from fire and
  minimized the effects of earthquake.
• The reason was to keep from destabilizing Eastern
  money markets and the economic interests of the
  railroad.
• Mayor Schmitz, members of the Board of
  Supervisors, the police chief, and coroporate
  members of the railroads and other utilities were
  indicted for bribe giving and taking both before
  and after the earthquake.

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Scientific Discovery

• The Lawson Report
• The Commission's final report, published in 1908,
  was an exhaustive compilation of detailed reports
  from more than twenty contributing scientists on
  the earthquake's damage, the movement on the San
  Andreas fault, the seismograph records of the
  earthquake from around the world, and the
  underlying geology in northern California.

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Theory of Elastic Rebound

• This theory, which forms the basis for our modern
  understanding of earthquakes, describes how the
  earth's crust gradually and elastically distorts
  with accumulating plate motion until it is
  suddenly returned to its undistorted state by
  rapid slip along a fault, releasing the years of
  accumulated strain and, in the process,
  generating seismic waves that produce shaking.
• 1906 earthquake essentially turned off
  earthquakes of magnitude about 6 and larger for
  the next 73 years.
• Central California has been experiencing a
  seismically quiet period caused by stress
  relaxation after 1906. The region may slowly be
  recovering from this "stress shadow" to a more
  normal state of seismicity as the tectonic plates
  continue to move, and the stresses on the major
  faults recover to the values that they had in
  1905.

Stress changes after 1906 for faults parallel to
the San Andreas. In blue regions, parallel faults
are less stressed in red regions, more stressed.
Nearly all major faults were relaxed after 1906.
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The Next One?

• The rate of large earthquakes in the San
  Francisco Bay region abruptly dropped after the
  Great 1906 Earthquake. The San Andreas Fault
  slipped so much over such a great length in that
  quake that the strain was reduced on most faults
  throughout the region. Strain has been slowly
  building up again. However, the level of seismic
  activity has not yet reached that of the late
  1800's.

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Probabilities

• The threat of earthquakes extends across the
  entire San Francisco Bay region, and a major
  quake is likely before 2030. Knowing this will
  help people make informed decisions as they
  continue to prepare for future quakes.

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Then Now

• If a similar earthquake occurred in Northern
  California today, after many decades of rapid
  urban growth, thousands of people would likely be
  killed, and economic losses might be in the
  hundreds of billions of dollars.
• Studies of earthquake shaking, active faults,
  and the response of structures to shaking have
  already led to improved building codes and a
  better understanding of how to reduce the threat
  posed by earthquakes.
• Damaging earthquakes are inevitable in the Bay
  region, but taking actions based on the odds of
  future quakes will help save lives and protect
  property.

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The 100th Anniversary April 18,
2006