Natural Disasters Report

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San Francisco

Often referred to as The City by the Bay, San Francisco, California is a city just that, a

city locked on three sides by water, the Pacific Ocean, the Golden Straight and the San Francisco

Bay. It is a city that stretches right to the waters edge and expands into the rolling hills of

Northern California, ultimately sitting 155 feet above sea level1. It has beautiful weather year

round, averaging at 58.6 F2. It sits on the edge of the San Francisco Bay and the Pacific Ocean.

According to the United States Census Bureau in 2009, the population of the city is 815,358.4

This large number of people fit into the city limits spreading 46.96 square miles.4

Most of the

population lives on the coast of the bay and then living quarters expand into the hills. Most of the

business scene is closer to the coast than inland; this can be seen in any general picture of the

city of San Francisco, such as the one below.5

1http://www.city-data.com/us-cities/The-West/San-Francisco-Geography-and-Climate.html

2http://www.city-data.com/us-cities/The-West/San-Francisco-Geography-and-Climate.html

3http://pubs.usgs.gov/gip/2005/15/

4http://quickfacts.census.gov/qdf/states/06/06075.html

5http://eugenecho.files.wordpress.com/2008/12/san_francisco_marin_view.jpg

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Though this may seem like the perfect place to live, San Francisco does have set backs. The city

is primarily, a major earthquake prone area that further results in other major hazards. Also, the

city has seen, in the past, the effects of El Nino and is again experiencing these rains this 2010

season.

Located in between the San Andreas Fault, on the west, and the Hayward Fault, on the

east, as seen in the figure below, San Francisco can experience earthquakes ranging from small

shakes to earthquakes above a magnitude 6.8, resulting in extensive amounts of damage and

casualties.

This image shows the

faults surrounding the San

Francisco area. The only

faults we are concerned

with are the San Andreas

Fault (yellow arrow) and

the Hayward Fault (red

arrow) because their

proximity to the city.7

This is an image

of the San Andreas

Fault; the red

arrows indicate the

movement of the

fault.3

7http://quake.usgs.gov/info/faultm aps/San_Francisco.html

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The San Andreas Fault and the Hayward Fault have both caused major earthquakes in the San

Francisco area. The San Andreas Fault extends from north to south across the state of California.

It is a strike-slip fault that is horizontally moving as fast a fingernail grows, which is

unfortunately always a threat to those living in San Francisco for earthquake occurrences.3

This

horizontal movement is due to the North American Plate moving to the right and the Pacific

Plate moving to the left, causing energy to be released, resulting in the earthquakes felt

throughout California. The Hayward Fault, extending for about 90 km from the Warm Springs

District of Fremont in the southeast to San Pablo Bay in the northwest,12

is a strike-slip fault

that also plays a part in the earthquakes in the San Francisco Area.

When an earthquake has occurred in the past by these faults, ground shaking within the

city caused a range of problems. First of all, the extent of ground shaking can range from small

movements to larger and more damaging movements. This can vary due to the magnitude of the

earthquake, the proximity an area is to the epicenter of an earthquake, and the ground on which

the area is built, either soft soil or hard soil. The problems that result are fires, damages bridges

and roads, broken water and power lines, liquefaction and surface ruptures3, as seen in the

collage of figures below.8,9,10,11

12http://geomaps.wr.usgs.gov/gump/people/ponce/hayward_fault/hf.html

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8,9,10,11

The ground shaking itself does not cause most of the casualties, but instead the resulting issues

of the ground shaking are the death of the population. Fires from broken power and gas lines

burn down the cites and because the water lines are damaged and roadways blocked, they spread

and grow quickly, devastating anything in its path. Liquefaction, the loss of support of in the

ground of the buildings in the city, destroy any structures above the now liquid like Earth,

8http://www.consrv.ca.gov/cgs/geologic_hazards/earthquakes/PublishingImages/SFEq06_03.jpg

9http://earthquake.usgs.gov/regional/nca/3Dgeologic/index.php

10https://reader009.{domain}/reader009/html5/0528/5b0b4ad4e272c/5b0b4ad844e08.jpg

11https://reader009.{domain}/reader009/html5/0528/5b0b4ad4e272c/5b0b4adb3b926.jpg

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including buildings and bridges, such as the well know San Francisco-Oakland Bay Bridge. This

results in, not only many causalities, but also great numbers of people left homeless and

desperate for help. This desperation and extent of damage and death was especially prominent in

the Great Earthquake of 1906. It was a magnitude of 7.8, where nearly 300 miles (480 km) of

the San Andreas Fault ruptured and practically the entire city of San Francisco burnt to the

ground. However, because of the great strength of the earthquake, a lot of the Earths stress and

energy was released, resulting in somewhat of a seismic gap in the following years. Due to this

time period of no great earthquakes, the city was able to repair the large losses and damages,

and actually grow exponentially. The city became and booming culture center during this time

known as the golden age.3

Since the great earthquake of 1906, only smaller earthquakes, yet still above a magnitude

5, have now occurred, releasing only 3% of the energy built up from this major earthquake3. One

smaller earthquake worth noting was the 1989 Loma Prieta earthquake, at a magnitude 6.9-7.03,5

.

Though it was over 50 miles south of San Francisco in the Santa Cruz mountains, the ground

shaking from the quake caused not only damage to the buildings, as seen below, from

liquefaction, but also collapsed areas to the San Francisco-Oakland Bay Bridge. Fires also

occurred in the city, but nothing as extensive as that of the 1906 earthquake, seen below as well,

5http://earthquake.usgs.gov/regional/nca/1906/18april/othereqs.php

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with only about 60 causalities in the 1989 earthquake, compared to the prior thousands of deaths

in the year of 1906.

Typical buildings in

San Francisco with a

soft ground level.

These will be highly

effected by a major

earthquake and the

liquefaction that

results, ending in

extensive damage as

seen in this image.3

The devastation from the fires that occurred after the

Great Earthquake of 1906 in San Francisco, CA.3

Though there was an extent of damage, this Loma Prieta earthquake was not the monster of an

earthquake that is said to come in the next twenty years. Since this is the fact of the matter, the

people of San Francisco need to be extremely prepared to be shaken up at any moment now by a

magnitude 6.7 or higher. According to www.wvdhsem.gov, San Francisco has a 70% odds for

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at least one magnitude 6.7 or greater quake [between] 2000 to 2030, as seen in the figure

below.6

Though earthquakes are the main natural disasters of the San Francisco area, there are some

other concerns to keep in mind when thinking of weather changes that could affect the people

living there.

El Nino rains have also been a problem to the people in San Francisco. Most winters in

the past decades have been weak rain seasons, resulting in even what can be considered dry

spells on the area. Due to the lack of rain, the people living in the area are not used to large

6http://www.wvdhsem.gov/WV_Disaster_Library/Library/Earthquake/MajQuake_files/image004

.jpg

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amount of rainfalls that are most likely to occur in the area sooner than later. This then results in

flooding and major water damages. Weather in San Francisco is so unpredictable and in the

winter of 1978-1979, San Francisco did experience an unexpected El Nino rain season. However,

since then, another large El Nino rain season has not occurred again, at least not until this year.

According to SFGate.com, Drought-busting El Nino has come to town, meaning that the rain

is back and flooding will occur.13

Though flooding is a problem here, it is certainly not going to

reach the extent of damaging that the Great Earthquake of 1906, the Loma Prieta Earthquake of

1989, and the monster earthquake to come in the next few years.

Returning back to the two largest earthquakes San Francisco has seen in the twentieth

century, the city has learned much from both occurrences to be prepared for the future larger

earthquake to come. Thought the people of the Bay Area were nowhere near prepared for the

earthquake of 1906, they were much more prepared for the 1989 earthquake. In 1906, many

more people lost their lives and the city receives much more damage to it than any earthquake

since. Buildings were not designed for the shaking and liquefaction that the quake would bring,

water and gas lines were not reinforced well enough to not break, and thus fires were not able to

be controlled, and rapidly spread, burning everything down in its path. However, San Francisco

has not seen this much damage since because of changes in mitigation efforts for future events,

13http://articles.sfgate.com/2010-01-21/news/17834651_1_el-ni-o-el-no-show-bay-area

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such as the 1989 event. After the Great Earthquake, most buildings were rebuilt to withstand

liquefaction and ground shaking. These designs included braced frames, seen below, which

resists lateral loads of shaking by bending beams and columns, and base isolation, which absorbs

seismic energy and allows building to move with ground and stop liquefaction of the buildings to

occur.14

Though there were measures taken to stop damaging from occurring when earthquakes hit the

area, when the Loma Prieta Earthquake hit in 1989, the Bay Bridge and some of the old

buildings, of which were not effected by prior earthquakes or torn down and rebuilt, were the

damaging results and the reason for causalities from these events. The 6.9-7.0 magnitude

14http://nisee.berkeley.edu/thumbnail/6257_3021_2284/IMG0060.jpg

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earthquake shook the city pretty strongly, which is seen in the shake map below, to still cause

some damage.3

Soft ground buildings, such as those with the garages sitting on the ground level of the

building as seen below, and the Bay Bridge fell in certain areas, resulting in disastrous sites that

left some people homeless or unable to travel, and even more awful, dead.15

15https://reader009.{domain}/reader009/html5/0528/5b0b4ad4e272c/5b0b4adf4f1ea.jpg

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Yes, mitigation efforts were better in this situation than in prior earthquakes, but even more is

being done now to make San Francisco even more of a livable and earthquake-proof city. The

areas that specifically needed to be focused on by those completing the mitigation efforts are the

oldest buildings in the city, as well as the bridges. Those living in the typical San Francisco style

buildings with space-conscious mind set, having the garages as their bottom floor, should

definitely think of moving out or petitioning for their building to be torn down and rebuild with

base isolations. Then, when the monster earthquake that is to hit does actually shake the city,

their entire building will not collapse below their feet, as less damage will occur to their homes.

With the bridges, the Golden Gate Bridge is built to withstand an earthquake of 8.0 or greater,

and now the Bay Bridge, which has seen great damage from prior earthquakes, is now being

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rebuilt, segment by segment, as seen below, to withstand the shame shakes the Golden Gate

Bridge is able to handle.16,17

With these new changes, the city of San Francisco is more prepared for future earthquakes, less

costly damages, and even smaller amounts of casualties, even if the ground shaking for a future

16http://www.inberkeley.com/wp-content/uploads/2009/09/Bay-Bridge-2..jpg

17http://www.revelationit.net/img/baybridge_project1_big.jpg

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earthquake is to be far worst than that of the 1989 Loma Prieta Earthquake, as shown in the

shake map below.18

In addition, there are ways that civilians of the city can prepare themselves for the future great

earthquake. When an earthquake does shake San Francisco, emergency services may not be

readily available due to damages in roads or other more important situations needed to be

attended, as well as damages to the facilities and amenities needed to assist civilians, such as

seen in the image below.3

18http://www.consrv.ca.gov/cgs/rghm/psha/index.htm

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Also, stores will most likely be damaged and thus, not open to the public. After earthquakes, the

American Red Cross will quickly tries to provide relief for the San Francisco population but

there are still measures the people of San Francisco should take themselves as well. Ranging

from personal kits, to household emergency kits, from particular setups of the furniture in the

home to what should be fixed to the structure of the building and what should be put away so as

not to fall when the shaking occurs, many different precautionary steps should be followed

before another great earthquake occurs in San Francisco, which could be sooner than one thinks.

All loose furniture and items should be reinforced to the structure of the building. All gas and

water lines should be changed from hard pipes to flexible pipes that can absorb shakes and be

less likely to break. Every family member should practice the drop, cover, and hold on and

find spaces in the house where collapse of ceilings and walls is less likely to happen, or places

that will protect a person from falling objects, as seen in the photo below.3

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Also, food, medication, water, a flash light, a

whistle and a First-Aid kit should all be

purchased and stored in an easily accessible area

so when an earthquake does occur, it can be

quickly accessed and thus bring relief until

emergency services are available and stores are

open.

Ways that civilians can know of an earthquake coming is by the outdoor public warning system,

which is a loud siren that goes off throughout California when any earthquake is going to hit. It

is far more accurate that years prior and will definitely have an impact on the evacuation or

covering of residents and visitors of the city, and greatly decrease the number of casualties.

From these previous natural disasters, the city of San Francisco has greatly improved

their preparedness for a future great earthquake. Though they were not prepared at all for the

earthquake in 1906 and somewhat prepared for the 1989 earthquake, the city has definitely

learned their lesson and has now taken even greater measures to decrease the number of

casualties and damages from future quakes. The city is now, more than ever, more welcoming of

a growth in population because of the livable environment and safeness of the city from future

disastrous situations. In short, San Francisco is, every day, becoming more and more able to

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handle a monster earthquake, what was once considered the greatest threat to those living

there.

* All References are footnoted and all citations for figures are at the end of the sentences that

refer the figure