U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2016–3020

Revised August 2016 (ver. 1.1)

Using information from 

recent earthquakes, 

improved mapping of 

active faults, and a new 

model for estimating 

earthquake probabilities, 

the 2014 Working Group 

on California Earthquake 

Probabilities updated 

the 30-year earthquake 

forecast for California. 

They concluded that there 

is a 72 percent probability 

(or likelihood) of at 

least one earthquake of 

magnitude 6.7 or greater 

striking somewhere in the 

San Francisco Bay region 

before 2043. Earthquakes 

this large are capable 

of causing widespread 

damage; therefore, 

communities in the region 

should take simple steps 

to help reduce injuries, 

damage, and disruption, 

as well as accelerate 

recovery from these 

earthquakes.

Map of known active faults in the San Francisco Bay region. The 72 percent probability 

of a magnitude 6.7 or greater earthquake includes the well-known major plate-boundary 

faults, lesser-known faults, and unknown faults. The percentage shown within each 

colored circle is the probability that a magnitude 6.7 or greater earthquake will occur 

somewhere on that fault system by the year 2043. The probability that a magnitude 6.7 or 

greater earthquake will involve one of the lesser-known faults is 13 percent.

1

11

22

2

12

21

3

13

23

4

14

24

5

15

25

6

16

27

7

17

26

8

18

9

19

10

20

28

29

30

31

32

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

Wight Way

Collayami

Mysterious Ridge

Bennett Valley

West Napa

Trout Creek

Point Reyes

Gordon Valley

Midland

Franklin

Southampton

Los Medanos-Roe Island

Pittsburg-Kirby Hills

Clayton

Mt. Diablo North

Mt. Diablo South

Pilarcitos

Las Positas

Orestimba

Monte Vista-Shannon

Silver Creek

Ortigalita North

Ortigalita South

Sargent

Zayante-Vergeles

San Joaquin

Reliz

Quien Sabe

Monterey Bay-Tularcitos 

Mission

Butano

Dunnigan Hills

Faults

Monterey

Bay

PA C I F I C

OCEAN

San Francisco Bay

0 10 20 KILOMETERS

0 10 20 MILES

HAYWARD

FAULT

CONCORD FAULT

RODGERS CREEK FAULT

MAACAMA FAULTMAACAMA FAULT

HUNTING

CREEK

HAYWARD

CONCORD FAULT

GREEN VALLEY

BERRYESSA

 GREENVILLE FAULT GREENVILLE FAULT

SAN ANDREAS FAULT

PAICINES FAULT

SAN ANDREAS FAULT

PAICINES FAULT

CALAVERAS

FAULT

CALAVERAS

FAULT

RODGERS CREEK FAULT

HUNTING

CREEK

SAN GREGORIO FAULT

33%

8%

16%

6%

22%

26%

San Francisco Bay Region

San Jose

Monterey

Salinas

Santa

Cruz

Half Moon

Bay

Point

Reyes

Mill

Valley

Napa

Santa

Rosa

Fremont

Oakland

San

Francisco

122°30’

38°

37°30’

38°30’

37°

122°

72%

probability of one or more

M ≥ 6.7 earthquakes

from 2014 to 2043 in the 

San Francisco Bay Region

Earthquake Outlook for the San Francisco Bay Region 2014–2043

3

EXPLANATION

Major plate boundary faults

Lesser-known smaller faults

Urban areas

Building damaged in 2014 South 

Napa earthquake. Photograph by 

Erol Kalkan, U.S. Geological Survey.
Earthquake Preparedness Helps

 Early Sunday morning on August 24, 

2014, the residents of Napa, California, 

were jolted awake by a strong, magnitude 

6.0 earthquake. Within 30 minutes, the 

staff of Becoming Independent, a nonprofit organization that helps adults with 

intellectual disabilities lead independent 

lives, called the people they serve in the 

affected area. The staff quickly visited 

all of the clients that needed help with 

cleanup and making their homes safe, 

a task made easier because both groups 

were trained in disaster preparedness 

and the clients had emergency kits with 

needed supplies on hand. The South 

Napa earthquake shifted houses off their 

foundations, damaged chimneys, started 

fires, and broke water mains throughout 

the city, causing hundreds of millions of 

dollars in economic losses. Many historic 

masonry buildings in downtown Napa 

were damaged. The earthquake was the 

largest in the San Francisco Bay region 

since the 1989 magnitude 6.9 Loma Prieta 

earthquake and a clear reminder of the 

seismic vulnerability of the region. The 

staff and clients of Becoming Independent 

showed that understanding and preparing 

for these events can improve how we live 

with future earthquakes.

Why Does the San Francisco Bay 

Region Have Earthquakes?

The same geologic process that is 

responsible for the San Francisco Bay 

region’s beautiful coastlines, bays, hills, 

and valleys is also the primary driving 

force for earthquakes along faults in 

the region. The Bay region is located 

within the active boundary between the 

Pacific and the North American tectonic 

plates, where the Pacific plate slowly 

and continually slides northwest past 

the North American plate. The San 

Andreas Fault, on which two magnitude 

7.8–7.9 earthquakes have occurred in 

historical time, including the 1906 San 

Francisco earthquake, is the fastest 

slipping fault along the plate boundary. 

Other major plate boundary faults in the 

San Francisco Bay region include the 

Hayward, Rodgers Creek, Calaveras, 

Maacama, San Gregorio, Concord,

Green Valley, and Greenville Faults. 

How Do Scientists Calculate 

Earthquake Probability?

Scientists rely upon a variety of 

techniques to help understand the rate and 

magnitude of past earthquakes in order 

to estimate the likelihood of future earthquakes. The Global Positioning System 

(GPS) and other land surveying 

and geologic techniques have allowed 

scientists to make more accurate measurements of how the current plate motions—

totaling 1.6 inches per year across the San 

Francisco Bay region—distribute stress 

onto these individual faults. Balancing 

plate motions with the slip during large 

earthquakes and slow creep on faults allows 

scientists to calculate average rates of earthquake occurrence over periods of hundreds 

to thousands of years. (Continued on page 4)

1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

72%

Probability

of at least one

magnitude 6.7

or greater quake

2014–2043

5.5–5.9 6.0–6.4 6.5–6.9 >7.0

Earthquake

magnitude

Increasing earthquake magnitude

6.5

6.8

6.9

5.5 5.5 5.5 5.5 5.5

5.5

5.5 5.5

5.5

5.6

5.6 5.6

5.6

5.7 5.7

5.6

5.7 5.7

5.8 5.8 5.8 5.8

5.8

5.8 5.8

5.9

5.9

5.9

5.9 5.9

5.9 5.9

7.8

5.9

5.9

5.9 6.0 6.1 6.0

6.1 6.1 6.1

6.2 6.3 6.3 6.3 6.1

6.1 6.2

6.4

6.1

6.4

1850–1966 earthquakes from Bakun, W.H., 1999, Seismic Activity of the San Francisco Bay Region: 

Bulletin Seismological Society of America, v. 89, p. 764–784 and 1967–2014 earthquakes from the Northern California Seismic Network.

Timeline of magnitude 5.5 and greater earthquakes in the 

San Francisco Bay region 1850–2014. In the 50 years prior to 

1906, there were 13 earthquakes with a magnitude between 

6 and 7, but only 6 earthquakes of similar magnitude in 

the 110 years since 1906. The rate of large earthquakes is 

expected to increase from this low level as tectonic plate 

movements continue to increase the stress on the faults in 

the region. 

San Francisco Bay Region Earthquake Timeline

2

Likelihood of at least one earthquake greater than a given 

magnitude in the San Francisco Bay region between 2014 

and 2043.

Magnitude 

(M)

30-year likelihood of at least one earthquake

in the San Francisco Bay region

M ≥ 6.0 98 percent

M ≥ 6.7 72 percent

M ≥ 7.0 51 percent

M ≥ 7.5 20 percent
Map of earthquakes greater than magnitude 2.0 in the San Francisco Bay region from 1985–2014. Small earthquakes occur on both major 

faults (shown by the gray lines) and minor faults (not shown). Because of the variability of fault geometry, earthquakes at depth do not always 

coincide with the mapped faults at the Earth’s surface. There are sections of major faults, particularly the San Andreas Fault, with few or no small 

earthquakes but they will produce large earthquakes in the future. Compiled from the Northern California Seismic Network.

Monterey

Bay

PA C I F I C

OCEAN San Francisco Bay

122°30’

38°

37°30’

38°30’

37°

122°

San

Francisco

Napa

Santa Rosa

Oakland

Hayward

Petaluma

Point

Reyes

Modesto

Healdsburg

Roseville

Watsonville

Concord

Vacaville

Novato

Gilroy

Livermore

Fairfield

Davis SACRAMENTO

San Jose

Vallejo

Santa

Cruz

Half Moon

Bay

Stockton

Salinas

Monterey

Earthquake

magnitude

1985–2014

S A N A N D R E A S

 F A U L T

2–3

3–4

4–5

5–6

6.9 Loma Prieta

Major faults

0 10 20

0 10 20

KILOMETERS

MILES

3
(Continued from page 2). A trench excavated 

across the Hayward Fault in Fremont revealed 

evidence of 12 large earthquakes over the past 

1,900 years. The time interval between these 

earthquakes ranged from about 100 to 210 

years. Historical records indicate that the most 

recent large earthquake on this fault occurred 

in 1868. However, detailed information about 

other past earthquakes in the San Francisco 

Bay region is difficult to obtain because seismograph records only go back to about 1900, 

historical accounts are sparse before 1850, 

and there are limited locations where faults 

can be trenched to identify and date prehistoric earthquakes. 

many of the faults in the region. However, 

the ongoing motion of the tectonic plates 

began rebuilding stresses after the 1906 

event, and earthquakes larger than magnitude 5.5 resumed during the second half of 

the 20th century. Future large, damaging 

earthquakes in the San Francisco Bay region, 

similar in size to the 1989 Loma Prieta and 

1906 San Francisco earthquakes, may or may 

not be accompanied by the level of earthquake activity observed in the late 1800s.

The 2014 Uniform California Earthquake Rupture Forecast version 3 (http://

pubs.usgs.gov/fs/2015/3009/) provides 

an updated estimate of the likelihood of 

large earthquakes in California over a 

30-year time window from 2014 to 2043. 

The forecast accounts for how fast stress 

is accumulating on each fault due to plate 

motions and the time since its most recent 

large earthquake(s). In updating the probability calculations, scientists used a more 

complete set of faults for the San Francisco 

Bay region than those used in the previous 

(2008) calculations, adding 32 smaller faults 

to the 5 major fault systems. The new study 

has also incorporated more options for how 

multiple faults might rupture together in 

large earthquakes.

Probabilities of Earthquakes in the 

San Francisco Bay Region

Smaller earthquakes occur more 

frequently than larger earthquakes. The 

probability that an earthquake of magnitude 6.0 or larger will occur before 2043 

is 98 percent. The probability of at least 

one earthquake of magnitude 6.7 or larger 

in the San Francisco Bay region is 72 

percent, and for at least one earthquake of 

magnitude 7.0 or larger it is 51 percent. 

These probabilities include earthquakes on 

the major faults, lesser-known faults, and 

unknown faults.

The probability of a large earthquake 

occurring on an individual fault in the San 

Francisco region is lower than the probability of an earthquake occurring anywhere in 

the region. The faults in the region with the 

highest estimated probability of generating damaging earthquakes between 2014 

and 2043 are the Hayward, Rodgers Creek, 

Calaveras, and San Andreas Faults. In this 

30-year period, the probability of an earthquake of magnitude 6.7 or larger occurring 

is 22 percent along the San Andreas Fault 

and 33 percent for the Hayward or Rodgers 

Creek Faults. Individual sections of these 

faults have lower probabilities for large 

earthquakes to occur (continued on page 6); 

4

PREPARE

Before the next big earthquake we 

recommend these four steps that will make 

you, your family, or your workplace better 

prepared to survive and recover quickly:

Step 1: Secure your space by identifying hazards 

and securing moveable items. Step 5: Drop, Cover, and Hold On when the earth 

shakes.

Step 2: Plan to be safe by creating a disaster plan 

and deciding how you will communicate in an 

emergency. 

Step 6: Improve safety after earthquakes by 

evacuating if necessary, helping the injured, and 

preventing further injuries or damage.

Step 3: Organize disaster supplies in convenient 

locations.

Step 7: Reconnect and Restore. Restore daily life 

by reconnecting with others, repairing damage, 

and rebuilding community.

Step 4: Minimize financial hardship by organizing 

important documents, strengthening your 

property, and considering insurance.

SURVIVE

During the next big earthquake, and 

immediately after, is when your level of 

preparedness will make a difference in how 

you and others survive and can respond to 

emergencies:

RECOVER 

After the immediate threat of the earthquake 

has passed, your level of preparedness will 

determine your quality of life in the weeks and 

months that follow:

Calculating accurate earthquake probabilities for short periods, such as 30 years, is

also challenging. Although the 30-year time 

interval is convenient for humans, it is much 

less than the average time between large 

earthquakes on these faults, which can range 

from hundreds to thousands of years. The 

rate of large earthquakes in the San Francisco Bay region was high in the late 1800s 

but dropped abruptly after the 1906 San 

Francisco earthquake on the San Andreas 

Fault. Scientists believe that the post-1906 

earthquake rate decreased because the large 

amount of slip along the San Andreas Fault 

in 1906 temporarily reduced the stress on 

Seven Steps to Earthquake Safety

Adapted from Seven Steps To Earthquake Safety

http://earthquakecountry.org/sevensteps/
5

San

Francisco

Napa

Santa Rosa

Oakland

Point

Reyes

Healdsburg

Roseville

Vacaville

Novato

Fairfield

SACRAMENTO

Fremont

San Jose

Vallejo

Half Moon

Bay

PA C I F I C

OCEAN

San Francisco Bay

122°30’

38°

37°30’

38°30’

122°

0

0

10

10

20

20

MILES

KILOMETERS

San

Francisco

Napa

Santa Rosa

Oakland

Hayward

Petaluma

Point

Reyes

Modesto

Healdsburg

Saint Helena

Roseville

Watsonville

Vacaville

Gilroy

SACRAMENTO

Concord

San Jose

Vallejo

Santa

Cruz

Half Moon

Bay

Stockton

Salinas

Monterey

Monterey

Bay

PA C I F I C OCEAN San Francisco Bay

Damage to engineered

structures and buildings 

Damage to older houses, 

chimneys, and masonry 

Objects thrown from

shelves, water sloshed

Sleepers wakened, felt 

by almost everybody

Felt by some people

in tall buildings

Fault rupture

Shaking effects

122°30’

38°

38°30’

37°30’

37°

122°

0

0

10 20

10 20

MILES

KILOMETERS

Maps showing intensity of ground 

shaking for the South Napa and 

Loma Prieta earthquakes. The black 

lines show the location of fault 

slip at depth. The maps illustrate 

how the area subjected to strong 

shaking increases with increasing 

earthquake magnitude.

1989 Magnitude 6.9

Loma Prieta Earthquake

2014 Magnitude 6.0

South Napa Earthquake

Road damage from the Loma Prieta 

earthquake. Photograph by H.G. 

Wilshire, U.S. Geological Survey.

Damaged building in downtown 

Napa. Photograph by Erol Kalkan, 

U.S. Geological Survey.
Additional Earthquake Resources

American Red Cross – Bay Area (http://www.redcross.org/local/northern-california-coastal) 

Association of Bay Area Governments (http://resilience.abag.ca.gov/earthquakes/)

Bay Area Earthquake Alliance (http://bayquakealliance.org/)

California Earthquake Authority (http://www.californiarocks.com/)

California Geological Survey 

(http://www.consrv.ca.gov/cgs/geologic_hazards/earthquakes)

Did You Feel It? (http://earthquake.usgs.gov/earthquakes/dyfi/)

Earthquake Country Alliance (http://earthquakecountry.org/)

Putting Down Roots in Earthquake Country (http://pubs.usgs.gov/gip/2005/15/)

ShakeAlert – An Earthquake Early Warning System for the United States West Coast 

(http://pubs.usgs.gov/fs/2014/3083/)

ShakeMap (http://www.cisn.org/shakemap/nc/shake/index.html)

ShakeOut.org (http://www.shakeout.org/california/bayarea/)

Uniform California Earthquake Rupture Fault version 3 Fact Sheet 

(http://pubs.usgs.gov/fs/2015/3009/)

United Policyholders (http://www.uphelp.org/)

USGS Real-Time Earthquakes (http://earthquake.usgs.gov/earthquakes/map/)

ISSN 2327-6916 (print) ISSN 2327-6932 (online)

http://dx.doi.org/10.3133/fs20163020

(continued from page 5) however, an 

earthquake of magnitude 6.7 or larger will 

cause strong shaking over a broad area. 

Therefore, it is important to estimate the 

probability of a large earthquake occurring 

anywhere in the San Francisco Bay region.

What is the Likelihood That an 

Earthquake Will Affect You?

Earthquake probabilities are only one 

component in the evaluation of earthquake 

hazards. Higher magnitude earthquakes 

have broader areas of intense shaking 

and cause more damage than lower 

magnitude earthquakes. In a magnitude 6.0 

earthquake, strong shaking and damage are 

confined to a localized area, as illustrated 

by the 2014 South Napa earthquake. In 

comparison, the 1989 magnitude 6.9 Loma 

Prieta earthquake caused damage over a 

region nearly 100 miles long. Local soil 

and geologic conditions, bedrock type, 

quality of building construction, and 

susceptibility to flooding (caused by dam 

or levee failure) can also affect the amount 

of damage at a particular site. This was 

dramatically demonstrated by the 1989 

Loma Prieta earthquake, which devastated 

vulnerable parts of Oakland and San 

Francisco, more than 50 miles from the 

fault rupture. 

How Can You Protect Yourself and 

Your Family?

Taking simple steps before and during 

earthquakes can help protect you and your 

family, as well as speed your recovery 

from an earthquake.

Damaged building in downtown Napa. Photograph 

by Erol Kalkan, U.S. Geological Survey.

Before the next earthquake:

• Assess your home and work space, 

identify hazards, and secure moveable 

items.

• Create an emergency plan and organize 

disaster supplies to sustain you and your 

family for 72 hours or longer.

• Practice “Drop, Cover, and Hold On” to 

protect yourself when the ground begins 

to shake. Learn and practice what to do 

at home, work, or in school. 

• Stay prepared by repeating these steps 

on a regular basis. For example, reassess 

your preparedness every year and 

participate in the annual Great California 

ShakeOut drill on the third Thursday in 

October. 

Brad T. Aagaard, James Luke Blair,

John Boatwright, Susan H. Garcia

Ruth A. Harris, Andrew J. Michael,

David P. Schwartz, and Jeanne S. DiLeo

Edited by Kate Jacques 

and Carolyn Donlin

For more information contact:

1-888-ASK-USGS

(1-888-275-8747)

http://earthquake.usgs.gov/

http://ask.usgs.gov

https://www.facebook.com/

USGeologicalSurvey

https://twitter.com/USGS

6

Lack of adequate shear 

walls on the garage 

level exacerbated 

damage to this building 

at the corner of Beach 

and Divisadero in the 

Marina District, San 

Francisco, during the 

October 1989 Loma 

Prieta earthquake.