| Earthquake Awareness and Preparedness |
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| Figure 1 - California Major Fault Lines USGS/SCEC permission, L.Gordon |
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| Figure 2 - Earthquake Prediction in Southern vs. Northern California USGS permission, Edward Field |
| Figure 3 - Earthquake Prediction of Major Fault Lines in Northern California USGS permission, Michael Diggles |
| Figure 4 - Major Fault Lines in Southern California SCEC permission, Leslie Gordon |
Earthquake Prediction in California
Earthquake prediction in California is an ongoing state-of-the-art research by the Working Group on
California Earthquake Probabilities (WGCEP), which is responsible for developing statewide,
time-dependent earthquake rupture forecasts that are endorsed by the United States Geological Survey
(USGS), the Southern California Earthquake Center (SCEC), and the California Geological Survey (CGS).
WGCEP predicts that California has a 99.7% probability of having an earthquake magnitude of 6.7 or larger
during the next 30 years.
Earthquake prediction in California is an ongoing state-of-the-art research by the Working Group on
California Earthquake Probabilities (WGCEP), which is responsible for developing statewide,
time-dependent earthquake rupture forecasts that are endorsed by the United States Geological Survey
(USGS), the Southern California Earthquake Center (SCEC), and the California Geological Survey (CGS).
WGCEP predicts that California has a 99.7% probability of having an earthquake magnitude of 6.7 or larger
during the next 30 years.
There are several earthquake sources (active faults) that can generate such a seismic event but with
different probabilities as shown in figure 1, which would probably be more powerful than the 1994
Northridge Earthquake. The southern segment of San Andreas Fault has the highest probability of
generating such an earthquake in Southern California with a 67% chance of striking the Greater Los
Angeles Area, while Hayward-Rodgers Creek Fault is the most likely earthquake source in Northern
California with a 63% chance of striking the San Francisco Bay Area. Larger earthquakes are less likely
during the 30 years time frame. The probabilities of earthquake magnitudes 7.0, 7.5, and 8.0 are 94%,
46%, and 4.5%, respectively. WGCEP predicts that an earthquake is more likely to occur in Southern
California than in Northern California for all earthquake magnitudes, as depicted on figure 2. Focusing on
Northern California, there is a 62% probability that at least one earthquake of magnitude 6.7 or greater will
occur in the San Francisco Bay Area before 2032. Hayward Fault has the highest chance of generating
such an earthquake event with a 27% probability. The northern segment of San Andreas Fault has a
probability of 21%, the Calaveras Fault 11%, the San Gregorio Fault 10%, as well as other faults shown in
figure 3.
different probabilities as shown in figure 1, which would probably be more powerful than the 1994
Northridge Earthquake. The southern segment of San Andreas Fault has the highest probability of
generating such an earthquake in Southern California with a 67% chance of striking the Greater Los
Angeles Area, while Hayward-Rodgers Creek Fault is the most likely earthquake source in Northern
California with a 63% chance of striking the San Francisco Bay Area. Larger earthquakes are less likely
during the 30 years time frame. The probabilities of earthquake magnitudes 7.0, 7.5, and 8.0 are 94%,
46%, and 4.5%, respectively. WGCEP predicts that an earthquake is more likely to occur in Southern
California than in Northern California for all earthquake magnitudes, as depicted on figure 2. Focusing on
Northern California, there is a 62% probability that at least one earthquake of magnitude 6.7 or greater will
occur in the San Francisco Bay Area before 2032. Hayward Fault has the highest chance of generating
such an earthquake event with a 27% probability. The northern segment of San Andreas Fault has a
probability of 21%, the Calaveras Fault 11%, the San Gregorio Fault 10%, as well as other faults shown in
figure 3.
California Earthquakes and Major Fault Lines
Earthquakes in California are developed by movement of two huge blocks of the earth’s crust: the Pacific
Plate and the North American Plate. The Pacific Plate is moving northwest, scraping horizontally past the
North American Plate at a rate of about 2 inches per year. Approximately two-thirds of this movement
occurs on the San Andreas Fault and some other parallel faults. Over time, these faults produce about half
of the significant earthquakes of the region, as well as many minor earthquakes. California Earthquakes
are initiated by rupturing of a fault line, propagating of seismic waves within the earth crust that will shake
the ground underneath the concrete foundations of a building. The intensity of the back- and forth- ground
shaking depends on the earthquake magnitude, the closest distance to the ruptured fault, and the type of
soil materials beneath the concrete foundations which may amplify the shaking. Soft soils in San
Francisco Bay Area would amplify and prolong the ground shaking even at great distances from the
ruptured fault, while hard bedrocks do not amplify the shaking. Deep soils in Los Angeles Basin would
shake more than bedrock in the hills as a result of persistent shaking where seismic waves are trapped
and reverberate. Unfortunately most urban development is in sedimentary basins. California hosts several
active fault lines that are identified in the USGS maps including San Andreas Fault, Hayward-Rodgers
Creek Fault, San Jacinto Fault, Elsinore Fault, Calaveras Fault, San Gregorio Fault, Garlock Fault, and
Imperial Fault. Any of these fault lines can generate an earthquake magnitude of at least 6.7 where their
approximate locations are shown on figures 2, 3 and 4.
Earthquakes in California are developed by movement of two huge blocks of the earth’s crust: the Pacific
Plate and the North American Plate. The Pacific Plate is moving northwest, scraping horizontally past the
North American Plate at a rate of about 2 inches per year. Approximately two-thirds of this movement
occurs on the San Andreas Fault and some other parallel faults. Over time, these faults produce about half
of the significant earthquakes of the region, as well as many minor earthquakes. California Earthquakes
are initiated by rupturing of a fault line, propagating of seismic waves within the earth crust that will shake
the ground underneath the concrete foundations of a building. The intensity of the back- and forth- ground
shaking depends on the earthquake magnitude, the closest distance to the ruptured fault, and the type of
soil materials beneath the concrete foundations which may amplify the shaking. Soft soils in San
Francisco Bay Area would amplify and prolong the ground shaking even at great distances from the
ruptured fault, while hard bedrocks do not amplify the shaking. Deep soils in Los Angeles Basin would
shake more than bedrock in the hills as a result of persistent shaking where seismic waves are trapped
and reverberate. Unfortunately most urban development is in sedimentary basins. California hosts several
active fault lines that are identified in the USGS maps including San Andreas Fault, Hayward-Rodgers
Creek Fault, San Jacinto Fault, Elsinore Fault, Calaveras Fault, San Gregorio Fault, Garlock Fault, and
Imperial Fault. Any of these fault lines can generate an earthquake magnitude of at least 6.7 where their
approximate locations are shown on figures 2, 3 and 4.
Earthquake Information on Soil Liquefaction
Liquefaction occurs during strong ground shaking for poorly-compacted artificial fill or sandy
soils with high ground water table. Partially saturated soil deposits may completely lose
cohesion during ground shaking, behaves like a liquid, and loses their ability to support the
concrete foundations of the building. Areas of liquefaction susceptibility are well-documented in
the USGS maps at http://earthquake.usgs.gov/regional/nca/qmap/. These areas include -but
not limited to- San Francisco Bay Area, Northwestern Alameda County, Northern Santa Clara
Valley, Southern Coachella Valley, and Upper Santa Ana River Basin.
Liquefaction occurs during strong ground shaking for poorly-compacted artificial fill or sandy
soils with high ground water table. Partially saturated soil deposits may completely lose
cohesion during ground shaking, behaves like a liquid, and loses their ability to support the
concrete foundations of the building. Areas of liquefaction susceptibility are well-documented in
the USGS maps at http://earthquake.usgs.gov/regional/nca/qmap/. These areas include -but
not limited to- San Francisco Bay Area, Northwestern Alameda County, Northern Santa Clara
Valley, Southern Coachella Valley, and Upper Santa Ana River Basin.
Northern California
Hayward fault generated an earthquake magnitude of 6.8 in 1868, which is considered as one
of the most destructive California Earthquakes in its history, although the region was sparsely
populated at that time. Currently, there are more than 2.4 million Californians in Alameda
County with hundreds of homes and other structures built directly on Hayward fault line trace. A
repeat of the 1868 Hayward Earthquake is expected to cause significant loss of life and
extensive damage to homes, businesses, transportation systems and utilities. Several hundred
thousand people are likely to be homeless after such an earthquake. Economic loss that
exceeds $120 billion is expected, which includes earthquake damage to buildings and their
contents, business interruption, and living expenses, with more than 90% of both residential
and commercial losses being uninsured.
Hayward fault generated an earthquake magnitude of 6.8 in 1868, which is considered as one
of the most destructive California Earthquakes in its history, although the region was sparsely
populated at that time. Currently, there are more than 2.4 million Californians in Alameda
County with hundreds of homes and other structures built directly on Hayward fault line trace. A
repeat of the 1868 Hayward Earthquake is expected to cause significant loss of life and
extensive damage to homes, businesses, transportation systems and utilities. Several hundred
thousand people are likely to be homeless after such an earthquake. Economic loss that
exceeds $120 billion is expected, which includes earthquake damage to buildings and their
contents, business interruption, and living expenses, with more than 90% of both residential
and commercial losses being uninsured.
Economic Loss and Earthquake Damage
Economic impact and structural damage from future California Earthquakes has been recently
studied separately for Northern California and Southern California. Generally speaking,
earthquake-related hazards including back- and forth- ground shaking, soil amplification,
liquefaction, landslides, and fires are the main reasons for earthquake damage to buildings. In
addition, building-related factors influencing the severity of structural damage includes building
materials, year built, number of stories, the size and spacing of anchor bolts that also may not
be adequately connected to the concrete foundations, the cripple walls in the crawl space being
unbraced nor strengthened, or the existence of a soft story where the first floor has large
openings (e.g. garage doors or windows) without being effectively braced. All these factors have
been demonstrated and well-documented after Northridge Earthquake and Kobe Earthquake
(1995) in Japan. Two building materials are not allowed anymore to be built in California:
unreinforced masonry construction and non-ductile reinforced concrete construction, because
they have poor performance during medium-to-large earthquakes and would be heavily
damaged, if not retrofitted. Wood construction, ductile reinforced concrete construction, and
steel frame construction generally perform better and are less likely to be damaged, especially
if located more than 20 miles from active fault lines.
Economic impact and structural damage from future California Earthquakes has been recently
studied separately for Northern California and Southern California. Generally speaking,
earthquake-related hazards including back- and forth- ground shaking, soil amplification,
liquefaction, landslides, and fires are the main reasons for earthquake damage to buildings. In
addition, building-related factors influencing the severity of structural damage includes building
materials, year built, number of stories, the size and spacing of anchor bolts that also may not
be adequately connected to the concrete foundations, the cripple walls in the crawl space being
unbraced nor strengthened, or the existence of a soft story where the first floor has large
openings (e.g. garage doors or windows) without being effectively braced. All these factors have
been demonstrated and well-documented after Northridge Earthquake and Kobe Earthquake
(1995) in Japan. Two building materials are not allowed anymore to be built in California:
unreinforced masonry construction and non-ductile reinforced concrete construction, because
they have poor performance during medium-to-large earthquakes and would be heavily
damaged, if not retrofitted. Wood construction, ductile reinforced concrete construction, and
steel frame construction generally perform better and are less likely to be damaged, especially
if located more than 20 miles from active fault lines.
California Earthquake Preparedness
Recent earthquakes such as the 2010 Haiti Earthquake and the 2011 Tohoku
Earthquake in Japan that generated a mega tsunami are reminders for
Californians to develop an earthquake preparedness and disaster
management plan to ensure home safety through seismic retrofit of home
structure and risk mitigation of home contents while reconsidering California
earthquake insurance, which is another effective way to protect the biggest
financial asset (home or business) and investments made in personal
possessions from the potential costs of destructive California Earthquakes,
especially if seismic retrofitting has not been done. Earthquake preparedness
also requires Californians to be aware of the location of their home/business
with respect to active major fault lines and liquefaction susceptibility areas
shown on the USGS maps, and basic knowledge on factors influencing
earthquake damage to their building. Emergency preparedness requires
purchasing an earthquake survival kit for the household, emergency kits for
household members, and maintaining emergency food and drinking water for
at least 2 weeks all-year round, as well as emergency training including
participation in earthquake drills. A tsunami warning device is also essential for
Californians living near the West Coast.
Recent earthquakes such as the 2010 Haiti Earthquake and the 2011 Tohoku
Earthquake in Japan that generated a mega tsunami are reminders for
Californians to develop an earthquake preparedness and disaster
management plan to ensure home safety through seismic retrofit of home
structure and risk mitigation of home contents while reconsidering California
earthquake insurance, which is another effective way to protect the biggest
financial asset (home or business) and investments made in personal
possessions from the potential costs of destructive California Earthquakes,
especially if seismic retrofitting has not been done. Earthquake preparedness
also requires Californians to be aware of the location of their home/business
with respect to active major fault lines and liquefaction susceptibility areas
shown on the USGS maps, and basic knowledge on factors influencing
earthquake damage to their building. Emergency preparedness requires
purchasing an earthquake survival kit for the household, emergency kits for
household members, and maintaining emergency food and drinking water for
at least 2 weeks all-year round, as well as emergency training including
participation in earthquake drills. A tsunami warning device is also essential for
Californians living near the West Coast.
Tsunami Warning
Tsunamis may hit the West Coast if a major earthquake displaces the floor of the Pacific Ocean. A tsunami
warning device such as an emergency radio or NOAA weather radio is essential for those living few miles
from the coast in tsunami-risk areas that are less than 25 feet above the ocean level. Another option is
“Disaster Alert” which is a free application available to Android-based and Apple-based mobile device
users. It is developed by the Pacific Disaster Center providing real-time data events on worldwide natural
disasters including a tsunami alert.
Tsunamis may hit the West Coast if a major earthquake displaces the floor of the Pacific Ocean. A tsunami
warning device such as an emergency radio or NOAA weather radio is essential for those living few miles
from the coast in tsunami-risk areas that are less than 25 feet above the ocean level. Another option is
“Disaster Alert” which is a free application available to Android-based and Apple-based mobile device
users. It is developed by the Pacific Disaster Center providing real-time data events on worldwide natural
disasters including a tsunami alert.
Emergency Training
Californians should register at http://www.shakeout.org/ to participate in the annual Great California
ShakeOut Earthquake Drill on October 20, 2011 at 10:20 a.m., which is a great opportunity to learn how to
protect yourself and your family during earthquakes. More than 7.9 million Californians participated in the
second annual earthquake drill in 2010.
Californians should register at http://www.shakeout.org/ to participate in the annual Great California
ShakeOut Earthquake Drill on October 20, 2011 at 10:20 a.m., which is a great opportunity to learn how to
protect yourself and your family during earthquakes. More than 7.9 million Californians participated in the
second annual earthquake drill in 2010.
Southern California
The southern segment of San Andreas Fault is the most likely earthquake source in Southern
California. Moreover, it is the only fault that can generate an earthquake magnitude of 7.8
because it has a very large fault area. According to this fact, a 2008 comprehensive research
study by the USGS and CGS on the structural damage and economic impact of a hypothetical
earthquake of magnitude 7.8 rupturing the southernmost 200 miles of the San Andreas Fault,
best known as: The Great California ShakeOut. The fault rupture will produce more than 100
seconds of ground shaking throughout Southern California. The event initiates from the
epicenter at the Salton Sea producing very strong ground shaking along the fault as it ruptures
until it ends near Lake Hughes, as shown in figure 5. Soil conditions at sites along the fault will
generally tend to amplify the earthquake shaking. The intensity of shaking will also be strong in
Los Angeles Basin and San Bernardino Valley. Landslides will mainly occur in the eastern San
Gabriel Mountains, while soil liquefaction will mainly occur in the southern Coachella Valley.
Localized liquefaction is likely to occur in the upper Santa Ana and Santa Clara River Basins. In
these areas of strong ground shaking and soil liquefaction, the ground will shift violently back
and forth collapsing thousands of older buildings, shoving houses off foundations, and sending
unsecured furniture and objects flying. Such an earthquake event will cause some 1,800 deaths
and 53,000 injuries. Fires are very likely to occur. Without fires, the casualty and loss numbers
would be halved. The estimated economic loss total $213 billion due to earthquake shaking
and its consequences specifically fires.
The southern segment of San Andreas Fault is the most likely earthquake source in Southern
California. Moreover, it is the only fault that can generate an earthquake magnitude of 7.8
because it has a very large fault area. According to this fact, a 2008 comprehensive research
study by the USGS and CGS on the structural damage and economic impact of a hypothetical
earthquake of magnitude 7.8 rupturing the southernmost 200 miles of the San Andreas Fault,
best known as: The Great California ShakeOut. The fault rupture will produce more than 100
seconds of ground shaking throughout Southern California. The event initiates from the
epicenter at the Salton Sea producing very strong ground shaking along the fault as it ruptures
until it ends near Lake Hughes, as shown in figure 5. Soil conditions at sites along the fault will
generally tend to amplify the earthquake shaking. The intensity of shaking will also be strong in
Los Angeles Basin and San Bernardino Valley. Landslides will mainly occur in the eastern San
Gabriel Mountains, while soil liquefaction will mainly occur in the southern Coachella Valley.
Localized liquefaction is likely to occur in the upper Santa Ana and Santa Clara River Basins. In
these areas of strong ground shaking and soil liquefaction, the ground will shift violently back
and forth collapsing thousands of older buildings, shoving houses off foundations, and sending
unsecured furniture and objects flying. Such an earthquake event will cause some 1,800 deaths
and 53,000 injuries. Fires are very likely to occur. Without fires, the casualty and loss numbers
would be halved. The estimated economic loss total $213 billion due to earthquake shaking
and its consequences specifically fires.
| Figure 5 - Ground Shaking Intensity in Southern California from M7.8 Quake source: California Institute of Technology Web Site |
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