Download 1906 San Francisco Earthquake

1906 SAN FRANCISCO
EARTHQUAKE
5:12 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
1906 San Francisco Earthquake
William Alexander Coulter’s (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.
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.
San Andreas Fault
San Andreas Fault
• Amount and
Rate of offset
variable.
• Consists of a
complex
system of
parallel and
interconnecting
faults.
April 18, 1906
• 5:12 AM – Initial foreshock
• 20-25 seconds later – The great
earthquake hits.
• Strong shaking lasted 45-60
seconds.
• Rupture length ~290 miles.
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.
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.
Predictive Intensity Map
1906 Earthquake Offset
1906 Earthquake Offset
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).
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)
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).
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)
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.
The City of San Francisco
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. Rooney’s 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.
Aftermath
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.
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.
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.
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.
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.
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.
The 100th Anniversary:
April 18, 2006