This activity is designed to provide a better understanding of
earthquake activity, the locations of faults, and earthquake hazards in the San Francisco bay
area. The activity utilizes a satellite image
of the bay area on which earthquake epicenters from 1970 - 2003 have been
plotted (Sleeter and others, 2004). The map is titled Earthquakes and Faults in the San Francisco Bay
Area (1970 - 2003) and can be found at: http://pubs.usgs.gov/sim/2004/2848/. To order copies of the map (Product Number
116286, Part Number SIM-2848, Scientific Investigations Maps series, $7 each;
$5 shipping and handling for entire order), call 1-888-ASK-USGS or order online
at: http://store.usgs.gov/. A reduced-size version of the map is provided
in Figure 1. We provide a digital image
of the map and an accompanying topographic base map (Figure 2) so that the
activity and associated materials are more readily available. The activity can be performed with the
reduced-size map (Figure 1, printed in color; can be printed or photocopy
enlarged to 11 x 17 inch paper size). However,
the landscape features and the epicentral patterns are more visible on the 84 x
117 cm (33" x 46") published map.
* MS Word and PDF versions of this document are
A previous version of this
activity using a 1990 USGS color poster (false-color satellite image and
is available at: http://web.ics.purdue.edu/~braile/edumod/bayarea/bayarea.htm. A PowerPoint presentation (including images
of the map, photos and images of the San Andreas fault zone, and information on
the 1906 San Francisco and 1989 Loma Prieta earthquakes) related to the new
(2004 map) activity can be found at: http://web.ics.purdue.edu/~braile/edumod/bayarea/BayAreaEQs.ppt.
Several attractive and useful
digital satellite images of the San
area are available at: http://www.sfbayquakes.org/. The images are available for download and
printing and can be displayed with or without faults plotted. An example of one of these images is shown in
Additional information on San Francisco Bay area earthquake activity, hazards
and earthquake forecasts can be obtained from USGS Fact Sheets (listed below in
reference section; also see http://water.usgs.gov/wid/indexlist.html
for an index of available fact sheets). Putting Down Roots in Earthquake Country
(San Francisco Bay
area version, USGS, 2005) has additional information about earthquakes and
earthquake hazards in the San
area. The recent article by Zoback
(2006) is also an excellent summary of earthquake activity in the bay area and
the 1906 event.
Satellite Image and Earthquake Map: The Earthquakes and Faults in the San Francisco Bay Area
(1970 - 2003) map (Sleeter and
others, USGS, 2004) is shown in Figure 1. The base map is a digital satellite image (Landsat
7 Enhanced Thematic Mapper Plus images) covering an area from about 36.2o
to 39 o North and about 120.9o to 123.7o
West. The original, full-size map is
plotted at a scale of 1:300,000.
Epicenters of earthquakes that occurred in the area from 1970 to 2003
are also shown. Faults are shown by bold
lines. Faults that are interpreted to
have been active in the last 700,000 years are indicated by red lines. Information on earthquakes of magnitude 5.0
or greater from 1970 - 2003 is listed a Table.
Epicenters for the 22 earthquakes in the Table are numbered on the
map. A topographic map of a portion of
the area shown in the satellite image is provided in Figure 2 for geographic
reference. An additional simplified map
of the geography and major faults of the area is shown in Figure 4.
Other Maps: A geologic map of the San Francisco Bay
area (Figure 5; Graymer and others, 2006), a map of active faults in the San Francisco Bay area (Figure 6; Graymer and others,
2006), and geophysical maps (http://geophysics.wr.usgs.gov/gump/zulanger/bayarea/bayarea.html)
including a Teacher’s Guide are also available.
The geologic and fault maps of the San Francisco Bay
area, including interactive versions and files for download, can be found at http://geomaps.wr.usgs.gov/sfgeo/index.html. To order copies of the geologic map (Product
Number 206043, Part Number SIM-2918, Scientific Investigations Maps series, $7
each; $5 shipping and handling for entire order), call 1-888-ASK-USGS or order
online at: http://store.usgs.gov/. To order copies of the quaternary-active
faults map (Product Number 206042, Part Number SIM-2919, Scientific
Investigations Maps series, $7 each; $5 shipping and handling for entire
order), call 1-888-ASK-USGS or order online at: http://store.usgs.gov/.
Additional information and
teacher resources on the San Francisco
Bay area, earthquakes, the San Andreas
fault and the 1906 San Francisco
earthquake can be found at: http://1906centennial.org/teachers/resources/. Very effective ground motion animations for San Francisco Bay
area earthquakes (1906 San Francisco
and 1989 Loma Prieta events) area available for viewing and download at: http://earthquake.usgs.gov/regional/nca/1906/simulations/.
Figure 1. Earthquakes
and Faults in the San Francisco
Bay Area (1970 - 2003)
map (USGS, 2004). The map can be viewed
online or downloaded from: http://pubs.usgs.gov/sim/2004/2848/. A full size pdf file an smaller jpg files are
Figure 2. Topographic
map of a portion of the area shown by the earthquake and fault map in Figure 1.
Figure 3. Perspective view digital satellite image of
the San Francisco area with young faults (active in the past 700, 000 years)
plotted in red. This image and
additional satellite images for the San
area are available at: http://www.sfbayquakes.org/.
Figure 4. Major faults in the San Francisco Bay
area. Map modified from Plafker, George
and Galloway, John P., Editors, 1989, Lessons Learned from the Loma Prieta,
California, Earthquake of October 17, 1989; U.S. Geological Survey Circular
1045, 48 p.
Figure 5. Geologic map of the San Francisco Bay
area (Graymer and others, 2006).
Figure 6. Quaternary-active fault map of the San Francisco Bay area (Graymer and others, 2006).
Hands-On Activity for the Classroom: (An efficient and effective strategy for
using this activity in the classroom is to obtain about 6 copies of the
earthquake map, laminate the maps for durability and marking with water soluble
felt pens, and place on tables in the classroom. Divide the students into groups and have them
examine and answer the questions and perform the tasks listed below. Each group should submit a written copy of
their answers and be asked to respond orally to one or more of the questions
during class discussion following the hands-on activity. A useful follow-up discussion or presentation
can focus on earthquake hazards and damage.
The PowerPoint presentation related to the San Francisco Bay
area earthquakes and fault map, http://web.ics.purdue.edu/~braile/edumod/bayarea/BayAreaEQs.ppt,
contains information, photos and images for this purpose.)
- Examine the Earthquakes
and Faults in the San
Area (1970 - 2003) map and the map legend. Note the map scale and sources of data
that are displayed on the map.
- Using the maps in Figure 2 and 4 or a road map or an
atlas, find the following geographic localities on the earthquake
Francisco, San Jose, Oakland, Santa Rosa, Santa Cruz, Monterey
Bay, Point Reyes, San Francisco Bay,
the Golden Gate Bridge, and the San Francisco Bay
- Find the following faults on the earthquake map: San Andreas Fault, Hayward Fault, Calaveras Fault,
Greenville Fault, Rogers Creek Fault, and San Gregorio Fault. For each fault, using your finger or a
pointer, trace each of the fault lines from northwest to southeast to see
the extent of the faults.
- Examine the
earthquake epicenters (yellow dots, size of the dot is proportional to the
magnitude of the earthquake) and trends or clusters of epicenters visible
on the map. Note that there are
several young (faults <700,000 years are plotted in red) fault segments
with very few earthquakes. What are
the possible explanations for this observation?
- Find the epicenters
for the 22 M5+ earthquakes that are listed in the Table of Earthquakes on
the map. Summarize the general
locations of these larger events (Are they located along a small number of
faults? Are they located in one
particular area of the map?)
- Find the
epicenters for the 22 M5+ earthquakes that are listed in the Table of
Earthquakes on the map. Summarize
the general locations of these larger events (Are they located along a
small number of faults? Are they
located in one particular area of the map?)
topographic or landscape features appear to be correlated with the young
faults on the map? Note that there
are significant young faults on both sides of the San Francisco Bay
and that this area is characterized by low elevations (below sea level of
slightly above sea level). This low
elevation area, generally, extends somewhat both northwest and southeast
of San Francisco
Bay. What are the possible geological
explanations for this low elevation area?
- Note that the
San Andreas Fault north of about Monterey Bay
is seismically relatively quiet.
This is a section of the fault that broke in the 1906 M7.8 San Francisco
earthquake. North of the map area,
the San Andreas extends to near Cape Mendocino making the 1906 fault break
about 450 km long. Is a “repeat” of
the 1906 earthquake along this section of the fault likely? What population centers are likely to be
affected by strong shaking from such an event?
- What other
significant faults (length greater than about 20 km, capable of generating
M6.5+ earthquakes) are close to population centers?
- Scientists know that buildings and other man-made
structures built on fill areas or areas of un-compacted sediments are more
likely to be damaged in an earthquake because these materials can
intensify shaking. Can you identify
areas on the map where relatively thick accumulations of these sediments
- Where is the plate boundary (on this map) between the
Pacific and North American tectonic plates? (Plate tectonic concepts can be
demonstrated using the hands-on activities, plate puzzle, http://web.ics.purdue.edu/~braile/edumod/platepuzz/platepuzz.htm,
and, teaching about plate tectonics and faulting using foam models, http://web.ics.purdue.edu/~braile/edumod/foammod/foammod.htm.)
- If the Pacific plate moves up the peninsula at an
average rate of 4 cm per year toward the northwest, how long will it take
for Santa Cruz (at the northern edge of Monterey Bay) to be due west of
Discussion of Earthquake Hazards and Forecasting in
the San Francisco
Bay Area: (This section is modified from
"San Francisco Bay Area Earthquakes Poster – A Teachers' Guide"
developed by the U.S. Geological Survey, 1990.
A copy of the text of the Teachers’ Guide can be found at: http://www.seismo.unr.edu/ftp/pub/louie/class/100/sf-class.html.)
Many people look at this map and
the trace of the San Andreas Fault just south of San Francisco and feel comforted by the fact
that there are so few earthquakes, when in fact, this area has one of the
higher probabilities for a large earthquake.
The presence of so many smaller earthquakes south of this section of the
fault attests to the fact that the stress is high along the San Andreas.
Scientists know that the Pacific
Plate is sliding to the northwest relative to the North American Plate at an
average rate of about 4 centimeters per year.
The faults in this area are the surface expression of the edges of these
two tectonic plates grinding past each other.
In fact, the movement along these faults is neither smooth nor
constant. The motion of the plates
builds up strain (stored elastic energy caused by deformation of the
lithosphere due to plate motions) along these faults until the stress becomes
too much and the built up pressure is released through an earthquake.
By studying these, and other
faults scientists recognize the patterns of earthquakes that relieve the stress
in this constantly moving system. The
history of earthquakes in the San
Francisco area suggests that this area is rocked
fairly regularly, on a geologic time scale, with large earthquakes. The seismicity gap, or lack of seismic
activity as evidenced along specific segments of the faults on this map, is
part of the temporal pattern of strain release for this part of the fault.
Scientists continue to study
earthquake patterns. As our
understanding of earthquake systems increases, so does our ability to predict
the impact on the human environment.
In the early to mid 1980s,
scientists began forecasting the Loma Prieta earthquake. Scientists had judged the Santa Cruz Mountain
section of the fault as having the highest probability of an earthquake of any
segment of the San Andreas Fault that had
ruptured in 1906.
In July of 1990, after the Loma
Prieta Earthquake, the National Earthquake Prediction Evaluation Council convened
a panel of experts to re-evaluate predictions for the San Francisco Bay
area. As reported in "The Next Big
Earthquake", a publication distributed through regional newspapers in the
San Francisco Bay area after the quake (copies of "The Next Big Earthquake"
are available from the U.S. Geological Survey's Earth Science Information
Center, ESIC, by calling (650) 329-4085), four fault segments in the Bay Area
have been identified as having large earthquake potential: "the peninsula segment of the San
Andreas fault between Los Gatos and Hillsborough; the Hayward fault between
Fremont and San Leandro; the Hayward Fault between San Leandro and San Pablo
Bay; and the Rodgers Creek fault between San Pablo Bay and Santa Rosa. The council estimated that the probability is
about 25 percent for a large earthquake on each one of these fault segments
within 30 years."
The article goes on to say,
"More importantly, when the probabilities of earthquakes on all of these
segments are combined mathematically, there is a 67 percent chance for at least
one earthquake of magnitude 7 or larger in the San Francisco Bay Area between
1990 and 2020. Such an earthquake could
strike at any time."
While we cannot predict the exact
date and time of an earthquake, nor can we control them, we know enough to
mitigate much of the damage that can be caused by an earthquake. Our schools play a critical role in educating
people about the potential hazards to human life and property and about appropriate
safety precautions in earthquake territory.
With this information, our students begin to learn about designing and
developing buildings and communities in balance with their natural environment.
Graymer, R.W, B.C. Moring, G.J. Saucedo, C.M. Wentworth, E.E. Brabb, and
K.L. Knudsen, Geologic Map of the San
Francisco Bay Region, U.S. Geological Survey, Scientific Investigations Map
2918, 2006 (also available online and for download at: http://geomaps.wr.usgs.gov/sfgeo/index.html).
Graymer, R.W, William Bryant, C.A. McCabe, Suzanne Hecker, and C.S.
Prentice, Map of Quaternary-active Faults
in the San Francisco Bay Region, U.S. Geological Survey, Scientific
Investigations Map 2919, 2006 (also available online and for download at: http://geomaps.wr.usgs.gov/sfgeo/index.html).
Major Quake Likely to Strike Between 2000 and 2030, U.S. Geological Survey
Fact Sheet 152-99, http://pubs.usgs.gov/fs/1999/fs152-99/
Progress Toward a Safer Future Since the 1989 Loma Prieta Earthquake, U.S.
Geological Survey Fact Sheet 151-99, http://pubs.usgs.gov/fs/1999/fs151-99/.
Putting Down Roots in Earthquake Country (San Francisco Bay
area version), U. S. Geological Survey, 2005, http://pubs.usgs.gov/gip/2005/15/.
Sleeter, B.M., J.P. Calzia, S.R. Walter, F.L. Wong, and G.J. Saucedo, Earthquakes and Faults in the San Francisco Bay Area (1970 - 2003), U. S.
Geological Survey Scientific Investigations Map 2848, 1:300,000 scale, 2004, http://pubs.usgs.gov/sim/2004/2848/.
Zoback, M.L., The 1906 earthquake and a century of progress in
understanding earthquakes and their hazards, GSA Today, volume 16, April/May, p. 4-11, 2006. (Also available online at: ftp://rock.geosociety.org/pub/GSAToday/gt0604-05.pdf.)
Earthquake file for the San
area for use with the Seismic Eruption software is located at: http://web.ics.purdue.edu/~braile/edumod/bayarea/bayarea.hy4.
The file contains earthquake data for
events of M1+ from 1973 - 2006.
modified November 19, 2006
The web page for
this document is:
Partial funding for this development
provided by the National Science Foundation.
Copyright 2000-06. L. Braile. Permission granted for reproduction for