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Earthquakes & the Hayward Fault
Pr esen t ed b y t h e UC Ber k el ey Sei sm o l o gi c a l La b o r a t o r y
Flour Mill, 1868 Hayward EQ
Courtesy of NISEE, EERC, UC Berkeley
What is an earthquake?
•An earthquake is what happens
when two blocks of the earth
suddenly slip past one another.
The surface where they slip is
called the fault or fault plane.
•The location below the earth’s
surface where the earthquake
starts is called the hypocenter, and
the location directly above it on the
surface of the earth is called the
epicenter.
What causes earthquakes to happen?
Answer: PL A TE
TE CTON I CS !
Plate Tectonics cause strain to build up  Earthquakes
relieve strain
•The surface of the earth is made up of
many different pieces, like a puzzle, that
keep slowly moving around, sliding past
one another and bumping into each
other. These puzzle pieces are called
tectonic plates.
•Since the edges of the plates are
rough, they get stuck while the rest of
the plate keeps moving. Finally, when a
plate has moved far enough, the edges
unstick on one of the faults and there is
an earthquake!
The Tectonic Plates
Why does the ground shake during an earthquake?
When the force of the moving tectonic plates finally overcomes the friction of the jagged
edges of the fault and it unsticks, all that stored up energy is released. The energy radiates
outward from the fault in all directions in the form of seis mic waves like ripples on a pond.
The seismic waves shake the earth as they move through it, and when the waves reach the
earth’s surface, they shake the ground and anything on it, like our houses and us!
•Two types of seismic
waves that shake the
ground in different ways as
they travel through it: P
waves and S waves . (see
diagram)
Example of a large earthquake:
See the YouTube video on our videos page
•P waves are faster than S
waves and less destructive
during an earthquake
because of their
considerably smaller
amplitudes.
•P waves in the earth’s
crust travel 5.5km/s or
12,375mph and S waves
travel 3.3km/s or
7,425mph. That means
that P waves in the crust
Three Main Types of Faults
A.) Strike-slip Fault:
caused by horizontal
compression, the two
blocks of rock move
laterally past each
other- the San Andreas and Hayward fault are both strike-slip faults
QuickTim e™ and a
TIFF (Uncom pres s ed) decom pres sor
are needed to s ee this picture.
B.) Normal Fault:
caused by extensional forces pulling the two blocks apart, one block drops down
in relation to the other- this type of fault forms mid-oceanic ridges
C.) Thrust (Reverse) Fault:
caused by compressional forces that shorten the two bodies, pushing one block
up relative to the other
How are Earthquakes Measured?
By Intensity
INTENSITY
(measures amount of shaking)
- Based on observations of
shaking/damage
- Location dependent
- Designed to relate earthquake
intensities to what average
person or building experiences.
- A more qualitative scale than
the Richter magnitude scale,
lacking energy levels
associated with various
earthquake intensities.
How are Earthquakes Measured?
Using Seismometers
•Seismologists use instruments called seismometers to measure and record
ground movement during an earthquake as a result of seismic waves. They
measure very tiny vibrations of the earth and tell us how the ground moves in
all directions (up/down, east/west, north/south).
•Seismometers are usually placed in very quiet locations: vaults, underground
in tunnels, boreholes, buildings, and the bottom of the ocean.
Seismometers over time
•The signals from all of these seismometers are recorded by special
computers, and scientists analyze this digital data to determine the size of
an earthquake.
How are Earthquakes Measured?
By Magnitude
MAGNITUDE (size of the E Q at its source)
•Seismometers record magnitude
•One number describes the quake
•Same number regardless of seismometer location
•Bigger magnitude means:
bigger affected area
longer rupture time
bigger offset
seismogram
•A logarithmic scale
amplitude increases by factor of 10 for each
magnitude unit
energy increases by factor of 30 for each magnitude
unit
for example, a magnitude 6 earthquake releases 30
times the energy of a magnitude 5 and has 10 times
greater amplitude
Where do the biggest earthquakes occur?
•About 90% of the world’s earthquakes
and 80% of the largest earthquakes, occur
on the “R ing of Fire,” an area along the plate
boundaries that encircles the basin of the Pacific
Ocean.
•The largest events: 1960 Chile
(M 9.5), 1964 Alaska (M 9.2),
2004 Sumatra (M 9.1)
•China earthquakes (1556
Shensi & 1976 Tangshan) both
had close to one million
fatalities.
Where are we in all this? Earthquakes in California
•California is very seismically active.
•The majority of large earthquakes in
California occur near the coast.
Earthquakes in the San Francisco Bay Area
•The Bay Area is home to many different
faults including: San Andreas Fault,
Calaveras Fault, and the Hayward Fault.
Bay Area EQs in the 75 yrs. before 1906
The impending “Big One”: A Ticking Time Bomb
•The Hayward Fault
is a ticking time
bomb: stress is
continually building
up on the Hayward
Fault.
•A large earthquake
is inevitable, but the
question is when will
it happen?
Forecast for the “Big One”
• There is a 63% chance that a
large earthquake (magnitude 6.7
or greater) will occur between
now and 2036 in the Bay Area.
• There is a 31% chance that it
will occur on Hayward Fault.
The Hayward Fault
•A major strike-slip fault
that runs through the
East Bay, including the
UC Berkeley campus
and football stadium
•3 - 9 mm/year surface creep
along Hayward fault  Creep at
Memorial Stadium (see picture
of displacement of two sections)
•Most likely Bay Area fault to produce an earthquake in the
future
•Last major earthquake on the Hayward Fault was in 1868 (M
~7.0), and it was called the “Great San Francisco Earthquake”
until 1906, when the real Great SF Earthquake hit on the San
Andreas Fault
Image: Google Earth Hayward Fault Tour
•Since there have not been any earthquakes >M5 on the
Hayward Fault since 1868, that means another “Big One” is
coming soon…
Creep on The Hayward Fault
•On Strike-slip Faults (like the Hayward Fault), there is something else in
addition to earthquakes that relieves strain from plate tectonics: C reep.
•According to the USGS, creep is basically “slow, more or less continuous
movement occurring on faults due to ongoing tectonic deformation.”
Creep on the Hayward
fault during 30 years.
(about 2.5mm/yr.)
Image Courtesy of Doris Sloan
Image Courtesy of Doris Sloan
But…even though creep relieves strain, it does not relieve enough stress to
prevent a large earhquake! So…large earthquakes can still occur on creeping
strike-slip faults.
Paleoseismology: A History of Hayward Fault EQs
Scientists can use paleoseismology to
determine information about past
earthquakes by drilling several meters
into the Earth and observing different
layers.
Photo Courtesy of
Rick McKenzie
Photo
Photo Courtesy
Courtesy of
of Peggy
Peggy Hellweg
Hellweg
Hayward Fault
History:
•1836 (M?)
•1868 (M~7.0)
Earthquakes Relieve Stress
•Earthquake relieve stress on faults, but
small earthquakes cannot relieve enough
stress to prevent a large one (big earthquake
is inevitable)
•For example, you would need about 32,000
magnitude 4.2 earthquakes to equal the
energy released by one magnitude 7.2!
•Over 10 years, that would mean about 9
earthquakes with magnitude 4.2 a day!
•A magnitude 7.0 earthquake slips about
90cm, but a magnitude 4.0 earthquake slips
only a few millimeters.
Graph shows stress levels greatly
decreasing after each major
earthquake
Hayward Fault Earthquake Simulation
Geology + Math + Physics + Supercomputers (which create
3D models of the fault) = Fault Rupture Simulations
Image Courtesy of USGS
See the video on our videos page
Hayward Scenario: Residential Damage
There will be more
damage in the
East Bay than in
San Francisco,
since the East Bay
is closer to the
fault.
Residential damage
occurs over a smaller
area than for
commercial buildings.
Why?
Residential building are
generally wood framed
=less damage
Image
Image Courtesy
Courtesy of
of USGS
USGS
Another Issue: Chaos on the Freeways
6 million vehicles in
the Bay Area =
about 1 million
people on the roads
 pile-ups
everywhere
Photo: USGS
Photo: USGS
Also, many bridges
and overpasses
collapse!
Photo: USGS
Which Bay Area freeways would be affected?
I-80 through
Berkeley
Approach to
Bay Bridge
101 south of San
Fran
Approaches to
San Mateo Bridge
What will happen to Bay Area bridges?
Bay Bridge
The new eastern section of the Bay Bridge,
which is expected to open in 2013, is being built to
withstand a major earthquake. The retrofit of the
western segment has been completed. The Bay
Bridge is considered an emergency "lifeline" route
to be used in disaster response activities. Thus,
when completed, it will be able to reopen quickly
following an earthquake.
Photo: USGS
Bay Bridge in Loma Prieta EQ 1989
For more information, visit:
http://baybridgeinfo.org/faqs
Problems to be ready for when the EQ hits:
•Our homes and buildings are much stronger and better designed than those
in the past; however, as the Kobe video showed, large ground motion can
send furniture and smaller objects flying. So, you should be sure to secure
large furniture to walls and carefully store breakable objects.
•Many injuries from earthquakes during the night come from cut feet. Keep
a pair of old shoes under your bed just in case!
•It is likely that emergency help may not be available for over 72 hours
following a damaging earthquake, so you should have enough water and
food stored in an earthquake kit.
•Basic utilities such as electricity, gas, and water can take weeks to recover,
so be prepared.
How can you prepare yourself for an earthquake?
Image Courtesy of USGS
“The best protection against the danger of earthquakes is not
the knowledge of the particular dates upon which they will
occur, but the realization that they may occur at any time.”
- Andrew Lawson, 1922
ABAG
Red Cross