San Andreas Fault Zone - The University of Akron

San Andreas Fault Zone - The University of Akron

Table of Contents
Abstract ........................................................................................................................................... 4
Southern California: Playing with Fire ........................................................................................... 4
Description of the Study Area ..................................................................................................... 5
Purpose of this Report ................................................................................................................. 9
Faults ............................................................................................................................................. 10
San Andreas Fault Zone ............................................................................................................ 11
San Jacinto Fault Zone .............................................................................................................. 17
Elsinore Fault Zone ................................................................................................................... 20
Whittier Fault ......................................................................................................................... 23
Newport-Inglewood-Rose Canyon Fault Zone ......................................................................... 23
Raymond-Hollywood-Santa Monica Fault Zone ...................................................................... 27
Imperial Fault Zone ................................................................................................................... 28
Sierra Madre Fault System ........................................................................................................ 31
Earthquake Laws ........................................................................................................................... 32
Field Act of 1933....................................................................................................................... 33
Alquist-Priolo Earthquake Fault Zoning Act ............................................................................ 35
Seismic Hazards Mapping Act .................................................................................................. 37
Natural Hazards Disclosure Act ................................................................................................ 38
Room for Improvement ............................................................................................................. 40
An Analysis of Southern California Zoning Codes ...................................................................... 42
Methodology ............................................................................................................................. 43
Banning ..................................................................................................................................... 45
Costa Mesa ................................................................................................................................ 49
Desert Hot Springs .................................................................................................................... 53
Fontana ...................................................................................................................................... 57
Hemet ........................................................................................................................................ 61
Seal Beach ................................................................................................................................. 63
Overview ................................................................................................................................... 67
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Conclusion .................................................................................................................................... 68
Works Cited .................................................................................................................................. 70
Table of Figures
Figure 1. Southern California consists of ten counties. (Source: U.S. Census Bureau) ............... 6
Figure 2. Major cities located in Southern California. (Source: U.S. Census Bureau) ............... 7
Figure 3. Earthquakes in Southern California from 1700-2004. (Source: State of California) ..... 8
Figure 4. Faults within Southern California (Sources: United States Geological Survey and U.S.
Census Bureau) ............................................................................................................................... 9
Figure 5. Movements along the San Andreas Fault Zone created Cajon Pass (shown here) and
many other similar passes, forcing all modes of transportation to leave Greater Los Angeles in
narrow bands. (Sources: ESRI and U.S. Geological Survey) ..................................................... 13
Figure 6. The San Andreas Fault Zone is the longest fault zone in Southern California. Shown
in an inset are the branches of the San Andreas Fault Zone around San Gorgonio Pass. (Sources:
U.S. Geological Survey and U.S. Census Bureau) ...................................................................... 16
Figure 7. The San Jacinto Fault Zone starts near San Bernardino, and ends in Imperial County.
(Sources: U.S. Geological Survey and U.S. Census Bureau) ...................................................... 19
Figure 8. The San Jacinto Fault Zone runs through a San Bernardino development along an area
of open space. (Source: Treiman) ................................................................................................ 20
Figure 9. The Elsinore Fault Zone, with the Whittier and Chino (also known as Central Avenue)
Faults and Lake Elsinore, shown in insets. (Sources: U.S. Geological Survey and U.S. Census
Bureau) .......................................................................................................................................... 22
Figure 10. The Newport-Inglewood-Rose Canyon Fault Zone runs parallel to the coast from
Beverly Hills to San Diego. (Source: U.S. Census Bureau and U.S. Geological Survey) ......... 25
Figure 11. Hot spots of population density in Huntington Beach generally follow traces of the
Newport-Inglewood Fault Zone. (Source: U.S. Census Bureau and U.S. Geological Survey) ... 26
Figure 12. The Raymond-Hollywood-Santa Monica Fault Zone runs either offshore or in
heavily-populated areas. (Sources: U.S. Geological Survey and U.S. Census Bureau) ............. 28
Figure 13. The Imperial Fault Zone connects to the San Andreas Fault Zone via the Brawley
Seismic Zone. (Source: U.S. Geological Survey and U.S. Census Bureau) ............................... 30
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Figure 14. The Sierra Madre Fault System runs along the foothills of the Sierra Madre
Mountains. (Sources: U.S. Geological Survey and U.S. Census Bureau) .................................. 32
Figure 15. An example of an official map of a Seismic Hazard Zone. This map is of the
Hayward Fault Zone in Fremont, located near Oakland. (Source: California Department of
Conservation) ................................................................................................................................ 40
Figure 16. Locations of cities whose General Plans were critiqued. (Source: U.S. Census
Bureau) .......................................................................................................................................... 44
Figure 17. The rubric used to critique Banning’s General Plan. ................................................. 46
Figure 18. Faults located in Banning. (Source: City of Banning) .............................................. 47
Figure 19. Banning’s General Plan Land Use Map. (Source: City of Banning) ........................ 48
Figure 20. The rubric used to critique Costa Mesa’s General Plan. ............................................. 50
Figure 21. An estimated fault map of Costa Mesa. (Source: City of Costa Mesa) ..................... 51
Figure 22. Costa Mesa’s General Plan Land Use Map. ................................................................ 52
Figure 23. The rubric used to critique Desert Hot Springs’ General Plan. ................................... 54
Figure 24. Faults near Desert Hot Springs. (Source: City of Desert Hot Springs) ..................... 55
Figure 25. Desert Hot Springs’ General Plan Land Use Map. (Source: City of Desert Hot
Springs) ......................................................................................................................................... 56
Figure 26. The rubric used to critique Fontana’s General Plan. .................................................. 58
Figure 27. Faults within the City of Fontana. (Source: City of Fontana) ................................... 59
Figure 28. Fontana’s General Plan Land Use Plan Map. (Source: City of Fontana) .................. 60
Figure 29. The rubric used to critique Hemet’s General Plan. .................................................... 62
Figure 30. Hemet’s General Plan Land Use Map, overlaid with fault zones in Hemet. (Sources:
City of Hemet and Hemet General Plan) ...................................................................................... 63
Figure 31. The rubric used to critique Seal Beach’s General Plan. ............................................. 65
Figure 32. Fault Zone Map for Seal Beach. (Source: City of Seal Beach) ................................. 66
Figure 33. Land Use Map for the City of Seal Beach. (Source: City of Seal Beach) ................. 67
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Abstract
This report is an analysis of the measures being taken to protect structures in Southern
California from earthquakes. Southern California consists of a ten county area, including
Bakersfield, Santa Barbara, Los Angeles, Riverside-San Bernardino, and San Diego, with an
estimated population of 22,422,614 residents. Laws, practices, and faults outside of this study
area were not considered for this project.
Fault ruptures produce minimal damage during earthquakes compared to liquefaction and
earthquake-induced landslides, both results of ground shaking. For these reasons, damage can
still occur far from epicenters. Proper planning, thorough geologic investigations, and strict
building codes are all needed to mitigate the threat posed by ground shaking from earthquakes.
California earthquake laws and General Plans were researched, and a personal investigation was
conducted to assess if municipalities were prepared for a significant earthquake.
The results of this project concluded that earthquake laws, including the Alquist-Priolo
Earthquake Fault Zoning Act and the Field Act, only apply to construction projects after the laws
were passed. Furthermore, General Plans emphasize growth more than safety. Better planning
and stricter laws are needed to lead Southern California towards being able to withstand a major
earthquake without significant damage.
Southern California: Playing with Fire
Southern California is known, among other things, for its frequent earthquakes.
However, the rugged mountains created by fault movements also factor into why this region is so
beloved. The greater Los Angeles area has a 67% chance of seeing an earthquake with a
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magnitude equal to or greater than M 6.7 – the magnitude of the 1994 Northridge Earthquake,
Southern California’s last major earthquake – during the next 30 years (United States Geological
Survey, 2008). The fault system which is widely believed to be the most at risk is the San
Andreas Fault, whose two previous ruptures south of San Bernardino were in 1680 and 1450
(City of Desert Hot Springs, 2000). The probability of a major earthquake anywhere along the
San Andreas in Southern California is 59% (United States Geological Survey, 2008). If a M 7-M
8 earthquake were to occur along the San Andreas Fault, at least $45 billion in damages are
likely (L.A.’s Killer Quake, 2007).
Description of the Study Area
Southern California consists of Santa Barbara, San Luis Obispo, Kern, Los Angeles,
Ventura, Orange, Riverside, Imperial, San Bernardino, and San Diego Counties. An estimated
22,422,614 people called this place home in 2008 (Census Bureau, 2010). Some major cities in
the study area include Bakersfield, Santa Barbara, Los Angeles, Long Beach, Anaheim, Santa
Ana, Riverside, San Bernardino, Palm Springs, and San Diego (Figures 1 & 2).
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Figure 1. Southern California consists of ten counties. (Source: U.S. Census Bureau)
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Figure 2. Major cities located in Southern California. (Source: U.S. Census Bureau)
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Figure 3. Earthquakes in Southern California from 1700-2004. (Source: State of
California)
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Figure 4. Faults within Southern California (Sources: United States Geological Survey and
U.S. Census Bureau)
Purpose of this Report
Historically, earthquakes have occurred more frequently in Southern California in the
past. Since 1933, when data was first accurately collected in Southern California, there have
been 60 earthquakes with magnitudes greater than M 5.5 (Figure 3) (Southern California
Earthquake Center, 2010). An examination of the earthquake record prior to 1933 shows how
earthquakes in Southern California may have been more frequent and powerful in the past than
in the present (Lin II and Beccera, 2010). The most recent earthquake to cause significant
damage in Southern California was the 1994 Northridge Earthquake, whose magnitude was M
6.7. While the 1992 Landers Earthquake, the 1999 Hector Mine Earthquake, and the 2010 El
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Mayor – Cucapah Earthquake were all greater than M 7, these three earthquakes occurred in the
sparsely-populated desert regions of Southern California and extreme northern Baja California,
therefore affecting relatively few Southern Californians (United States Geological Survey, 2008).
The long period of time the urbanized areas of Los Angeles and San Diego have seen without a
significant earthquake, as well as the relative quiescence of the San Andreas Fault, or any other
fault within its system, could indicate that they are overdue. Structurally-sound buildings in
close proximity to the faults will be vulnerable in a major earthquake.
The purpose of this report is (1) to describe the spatial relation between fault zones in
Southern California and buildings, and (2) to suggest preventative safety measures to make
Southern California as safe as possible in the event of a major earthquake.
Faults
Southern California is located along the plate boundary between the Pacific and North
American Plates. Due to the plate movements, most faults in Southern California are either
right-lateral (also known as dextral) strike-slip faults or thrust faults (Huang, 1997). While a
majority of faults fit into either of these two categories, there are some notable exceptions, such
as the Garlock Fault, which is a left-lateral (also known as sinistral) strike-slip fault (Figure 4)
(Southern California Earthquake Center, 2010). Approximately 75% of fault movement along
the Pacific-North American plate boundary is accommodated by the San Andreas Fault and its
“sister” faults – the Imperial, San Jacinto, Elsinore, and Newport-Inglewood-Rose Canyon Fault
Zones (Guest, Niemi, and Wernicke, 2007). The other 25% of fault movement along the PacificNorth American plate boundary is accommodated by faults in the Mojave Desert (Guest, Niemi,
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and Wernicke, 2007). In recent years, most of the major earthquakes have happened in the series
of faults in the Mojave Desert, known as Walker Lane (McGill, 2007).
Many of the thrust faults have no surface trace (L.A.’s Killer Quake, 2007). These faults,
known as blind thrust faults, can be particularly damaging. Because these fault planes lie
kilometers underground, their presence is only noticed when recordable seismic events occur
(L.A.’s Killer Quake, 2007). Two blind thrust earthquakes were the 1987 Whittier Narrows
Earthquake and the 1994 Northridge Earthquake, which occurred on what would later be named
the Puente Hills Fault and the Pico Thrust, respectively (L.A.’s Killer Quake, 2007). The Puente
Hills Fault, which is located under Downtown Los Angeles and the USC campus has planners
and emergency workers concerned (L.A.’s Killer Quake, 2007). Some suggest recurrence
intervals – how frequently events occur – for such faults are likely to be very long, thus making
the general population uninformed regarding the threat such faults pose (L.A.’s Killer Quake,
2007).
San Andreas Fault Zone
The San Andreas Fault Zone (Figure 6) is the most heavily-studied fault zone in the
world. Upon leaving Northern California and entering Southern California, the San Andreas,
which acts as the boundary between the North American and Pacific Plates, passes through or
near the communities of Frazier Park, Palmdale, Wrightwood, San Bernardino, Palm Springs,
and Indio, among many others (Southern California Earthquake Center, 2010). In Southern
California, the San Andreas can be divided into four segments, each with different
characteristics: the Carrizo Plain segment, which experiences frequent, moderate earthquakes
along with the occasional large earthquake; the Mojave segment, which tends to have few
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moderate earthquakes but damaging large earthquakes; the San Bernardino Mountains/San
Gorgonio Pass segment, where the main strand of the San Andreas branches off in to numerous
faults; and the Coachella Valley segment, which has not seen a major event since 1690 (Southern
California Earthquake Center, 2010).
The San Andreas has been crucial in the formations of Tejon and Cajon Passes, where
Interstates 5 and 15 cross the faults, respectively (Figure 5) (Treiman, 2007). Tectonic
deformation is also evident in a rock cut on the outskirts of Palmdale, where California State
Route 14 crosses the fault (Treiman, 2007). As the southern boundary of the Mojave Desert, the
northern boundary of the San Gabriel Mountains, and the southern boundary of the San
Bernardino Mountains, it is clearly visible from space. Development is beginning to encroach
upon the fault due to the scenery, especially in the San Bernardino and Highland areas (Treiman,
2007).
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Figure 5. Movements along the San Andreas Fault Zone created Cajon Pass (shown here)
and many other similar passes, forcing all modes of transportation to leave Greater Los
Angeles in narrow bands. (Sources: ESRI and U.S. Geological Survey)
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The San Andreas Fault Zone splits up into multiple strands in San Bernardino. The Mill
Creek Fault leaves the main strand near Arrowhead Springs, while the Mission Creek Fault
leaves near the main fault near Mentone and connects with the Mill Creek Fault before leaving
the San Bernardino Mountains (Southern California Earthquake Center, 2010). The latter fault
connects to the Banning Fault, considered by geologists to be the dominant strand of the San
Andreas, near Indio. Back to the west, the main strand of the San Andreas Fault Zone appears to
be divided from the Banning Fault by the Gandy Ranch Fault, near Cabazon (Southern
California Earthquake Center, 2010). It is important to note that earthquakes have historically
ruptured the Coachella Valley, San Bernardino Mountains/San Gorgonio Pass, and the Mojave
segments simultaneously.
The Banning Fault, which continues to the west past the San Andreas, is considered
inactive west of Banning (Southern California Earthquake Center, 2010). East of Banning, its
trace is often interrupted by the San Gorgonio Thrust, which has displaced the Banning Fault in
numerous locations (Southern California Earthquake Center, 2010). Upon leaving the San
Gorgonio Pass, the Garnet Hill Fault branches off of the Banning Fault and heads towards the
central business districts of Palm Springs and Palm Desert. The Banning Fault and the Mission
Creek Fault merge near Indio to form a single San Andreas Fault, which continues until its end
near Bombay Beach, on the shores of the Salton Sea (Figure 6). The next major earthquake is
expected here. Due to the amount of strain, its recurrence interval, and when it last ruptured
(1680), geologists who have studied the fault believe it could rupture any day in a cataclysmic
event, the likes of which Southern Californians have not experienced since 1857, when the Fort
Tejon Earthquake (M 7.9) ruptured the San Andreas Fault from Parkfield to Cajon Pass
(Southern California Earthquake Center, 2010).
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A major earthquake would have lasting effects on Southern California, although much of
it would be spared from heavy ground shaking. For instance, a major earthquake along the San
Andreas, possibly exceeding M 8, would likely cause long-term closures at the three
aforementioned high-importance transportation corridors, causing nearly 400,000 commuters to
be stranded from their workplaces and/or homes on the other side of the fault (Census Bureau,
2010; Treiman, 2007). Furthermore, potentially disruptive fires could occur from downed
utilities crossing the fault. Southern California’s aqueducts would also be severed, needing
immediate replacement.
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Figure 6. The San Andreas Fault Zone is the longest fault zone in Southern California.
Shown in an inset are the branches of the San Andreas Fault Zone around San Gorgonio
Pass. (Sources: U.S. Geological Survey and U.S. Census Bureau)
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San Jacinto Fault Zone
The San Jacinto Fault Zone (Figure 7) is the most active fault zone in Southern California
(Southern California Earthquake Center, 2010). The fault zone, which is 210 km long if the
Coyote Creek Fault is included with the fault zone, is a right-lateral strike slip fault with a minor
component of right-reverse faulting (Southern California Earthquake Center, 2010). The fault
begins to the north near Lytle Creek as a series of parallel faults less than two miles from the San
Andreas Fault Zone. It then passes the major city of San Bernardino, where it inconspicuously
passes directly under the interchange of I-10 and I-215. From there, the fault zone, which ranges
in width from 500 feet-12 miles, passes through Moreno Valley, San Jacinto, and Hemet, before
ending southwest of the Salton Sea near Imperial (Southern California Earthquake Center, 2010).
Scientists believe that the fault is capable of earthquakes up to M 7.5. Recent studies suggest
that aseismic creep occurring approximately 10 kilometers underground could lead to milder,
more frequent earthquakes (Nature Geoscience, 2009). Verification of this hypothesis comes
from recent earthquakes along this fault occurring in 1890, 1892, 1899, 1918, 1923, 1937, 1942,
1954, 1968, 1987, and 2010 (Southern California Earthquake Center, 2010). Another related
idea suggests the 1857 Fort Tejon Earthquake along the San Andreas Fault Zone increased stress
farther down the San Jacinto Fault Zone, with the first earthquake occurring near San Jacinto in
1899 (Reich, 1993). With the exception of the 1923 earthquake, which occurred near Loma
Linda, each following earthquake progresses farther down the fault (Reich, 1993). The
southernmost earthquake was the 1987 Superstition Hills Earthquake (Reich, 1993). The
hypothesis would then suggest that an earthquake would be expected next near the Mexican
border. Whether the 2010 El Mayor – Cucapah Earthquake, which occurred along multiple
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faults within the Laguna Salada Fault Zone, the logical extension of the parallel Elsinore Fault
Zone, supports this line of reasoning remains to be decided (EERI, 2010).
What makes the San Jacinto Fault Zone different from many other fault zones in
Southern is the effort businesses and municipalities are making to relocate buildings on or along
the fault zone. San Bernardino Valley College in San Bernardino is in the midst of a massive
campaign to relocate 8 of the 15 buildings on campus, including its historic library, to make the
campus safer (San Bernardino Valley College, 2010). Furthermore, suburban developments
along the fault zone are accommodating the location of the fault zone into plans, such as a
private development in extreme southern San Bernardino (Figure 8). However, there is still
significant progress that needs to be made in order for fault rupture to be a less important factor
along this fault zone.
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Figure 7. The San Jacinto Fault Zone starts near San Bernardino, and ends in Imperial
County. (Sources: U.S. Geological Survey and U.S. Census Bureau)
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Figure 8. The San Jacinto Fault Zone runs through a San Bernardino development along
an area of open space. (Source: Treiman)
Elsinore Fault Zone
One of the quietest fault zones in Southern California, the Elsinore Fault Zone (Figure 9)
has only produced one significant earthquake in its history: the 1910 Temescal Valley
Earthquake (M 6.0), which didn’t produce a surface rupture (Southern California Earthquake
Center, 2010). This right-lateral strike-slip fault runs for 180 km, making it one of the longest
fault zones exclusively in Southern California. The Elsinore Fault Zone starts in southwestern
Corona at the junction of the Whittier and Chino Faults, and runs through the cities of Lake
Elsinore, Wildomar, Murrieta, Temecula, and Julian (Figure 9) (Southern California Earthquake
Center, 2010). The fault zone is then cut off by the Yuha Wells Fault in southwestern Imperial
County from the Laguna Salada Fault, one of the faults involved in the 2010 El Mayor –
Cucapah Earthquake (EERI, 2010). Recently, scientists have observed an increase in earthquake
activity along the southern portion of the fault zone, perhaps suggesting that a major earthquake
is imminent (Lin II, 2010). With a recurrence interval of 250 years and the most recent surface
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rupture occurring in the 18th century, an earthquake here is overdue (Southern California
Earthquake Center, 2010). Research has indicated that the most probable magnitude range
would be from M 6.5 – M 7.5 (Southern California Earthquake Center, 2010). The Elsinore
Fault Zone’s multiple fault strands form a rift valley between Corona and Temecula, and Lake
Elsinore was formed from movement between parallel stands creating a depression which
eventually became filled with water (Figure 9) (Southern California Earthquake Center, 2010).
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Figure 9. The Elsinore Fault Zone, with the Whittier and Chino (also known as Central
Avenue) Faults and Lake Elsinore, shown in insets. (Sources: U.S. Geological Survey and
U.S. Census Bureau)
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Whittier Fault
The Whittier Fault (Figure 9), a right-lateral strike-slip fault, starts in southwestern
Corona, at the junction of the Chino and Elsinore Faults (Southern California Earthquake Center,
2010). It acts as the northwestern continuation of the Elsinore Fault Zone, running through
Anaheim, Yorba Linda, Brea, La Habra, and Whittier (Southern California Earthquake Center,
2010). The location of the fault in urbanized eastern Los Angeles, northern Orange, and extreme
western Riverside Counties makes it one of the most threatening faults in Southern California.
The length of the fault is only about 40 km, with likely earthquake magnitude ranges from M
6.0- M 7.2 (Southern California Earthquake Center, 2010). The Whittier Fault has ruptured in
the last 10,000 years, although the most recent rupture was before European settlement (Southern
California Earthquake Center, 2010). A M 4.2 earthquake in 1976 shows that this fault is still
seismically active, and is capable of a major earthquake (Southern California Earthquake Center,
2010). The Whittier Narrows Earthquake Sequence of 1987 and the 2008 Chino Hills
Earthquake both occurred near the fault, but the main shock occurred on separate fault systems
(Southern California Earthquake Center, 2010).
Newport-Inglewood-Rose Canyon Fault Zone
The Newport-Inglewood-Rose Canyon Fault Zone (Figure 10), a right-lateral strike-slip
fault system, is actually two fault zones: the 75 km long Newport-Inglewood Fault Zone in Los
Angeles and Orange Counties and the roughly 30 km long Rose Canyon Fault Zone, located
entirely within the City of San Diego (Southern California Earthquake Center, 2010). The
offshore portion which is believed to connect the two is poorly understood; what research which
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has been conducted, though, reveals that it is not likely to be continuous through this portion.
However, the two fault zones have similar strikes and dips, so some geologists consider those
faults to be part of a continuous fault zone (Southern California Earthquake Center, 2010)
The Newport-Inglewood Fault Zone starts in Bel Air, and then runs through Culver City,
Gardena, Compton, Long Beach, Signal Hill, Seal Beach, Huntington Beach, and Newport
Beach, all before it goes offshore (Figure 10) (Southern California Earthquake Center, 2010).
The most recent earthquake, the 1933 Long Beach Earthquake (M 6.4), was so damaging in
Long Beach that the Field Act, a law written to make schools structurally sound, was passed as a
response to it (Southern California Earthquake Center, 2010). The fault zone runs through dense
development, which often encroaches upon the fault zone, whose expected magnitude ranges
from M 6.0 – M 7.4 (Southern California Earthquake Center, 2010). In Huntington Beach, the
fault zone divides into numerous strands, some of which run through hot spots of population
density within the city (Figure 11). The fault zone goes offshore near Balboa Island in Newport
Beach.
The Rose Canyon Fault Zone reemerges in La Jolla (Southern California Earthquake
Center, 2010). In this affluent community, the fault zone often lies beneath homes and
businesses. To the south, the fault zone then follows Rose Canyon down to San Diego Bay
(Southern California Earthquake Center, 2010). Rose Canyon is a major transportation corridor
in San Diego, and the canyon carries I-5 and railroad tracks until close to Downtown San Diego.
The fault zone has experienced fault rupture in Holocene times, but the fault zone has not
experienced earthquakes since European settlement (Southern California Earthquake Center,
2010).
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Figure 10. The Newport-Inglewood-Rose Canyon Fault Zone runs parallel to the coast
from Beverly Hills to San Diego. (Source: U.S. Census Bureau and U.S. Geological
Survey)
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Figure 11. Hot spots of population density in Huntington Beach generally follow traces of
the Newport-Inglewood Fault Zone. (Source: U.S. Census Bureau and U.S. Geological
Survey)
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Raymond-Hollywood-Santa Monica Fault Zone
The Raymond Fault starts at the Sierra Madre Fault Zone in Duarte, and heads southwest
through Pasadena (Figure 12) (Southern California Earthquake Center, 2010). This left-lateral
strike-slip fault zone, 65 km in length, is actually considered to be three separate fault zones
(Southern California Earthquake Center, 2010). The recurrence interval is noticeably long,
ranging from 1600-4500 years (Southern California Earthquake Center, 2010). The most recent
earthquake along the Raymond Fault, the 1988 Pasadena Earthquake (M 5.0), was not a
destructive event (Southern California Earthquake Center, 2010). The Raymond Fault ends in
the Highland Park neighborhood of Los Angeles. The Hollywood Fault reappears a mile west of
the western terminus of the Raymond Fault in the Los Feliz neighborhood of Los Angeles
(Southern California Earthquake Center, 2010). It then runs through Glendale and Beverly Hills
before being offset by the northern terminus of the Newport-Inglewood Fault Zone (Figure 12).
The Hollywood Fault has not experienced a notable earthquake in recent history, despite being
the most active portion of the fault zone (Southern California Earthquake Center, 2010). West of
the Newport-Inglewood Fault Zone’s offset, the Santa Monica Fault straddles the communities
of Westwood and Santa Monica before terminating at the Malibu Coast Fault (Figure 12)
(Southern California Earthquake Center, 2010). While each section can produce earthquakes
themselves, the most dangerous aspect of this fault zone is that one rupture can produce rupture
along an adjacent fault, much like what happened in the 1992 Landers Earthquake, a M 7.3 event
(Southern California Earthquake Center, 2010).
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Figure 12. The Raymond-Hollywood-Santa Monica Fault Zone runs either offshore or in
heavily-populated areas. (Sources: U.S. Geological Survey and U.S. Census Bureau)
Imperial Fault Zone
The Imperial Fault Zone (Figure 13), which starts south of the Salton Sea near Brawley,
is the principal plate boundary between the North American and Pacific Plates south of the
Salton Sea (Southern California Earthquake Center, 2010). Geologists consider it to be
connected to the southern terminus of the San Andreas Fault Zone via the Brawley Seismic
Zone, an ill-defined zone of seismicity between Bombay Beach and the seismic zone’s
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namesake, Brawley (Figure 13) (Southern California Earthquake Center, 2010). Its total length
is 69 km (Southern California Earthquake Center, 2010).
The towns of Brawley, El Centro, and Calexico are near the Imperial Fault Zone (Figure
13). The 30-40 year recurrence interval along this fault suggests earthquakes will be both
frequent and comparatively mild to the San Andreas (Southern California Earthquake Center,
2010). The fault has ruptured many times in recorded history, with earthquakes between M 6
and M 7 occurring in 1915, 1940, and 1979 (Southern California Earthquake Center, 2010). A
M 3.6 along the Imperial Fault on March 4, 1966 was the smallest tectonic event ever to produce
a surface rupture (Southern California Earthquake Center, 2010).
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Figure 13. The Imperial Fault Zone connects to the San Andreas Fault Zone via the
Brawley Seismic Zone. (Source: U.S. Geological Survey and U.S. Census Bureau)
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Sierra Madre Fault System
The Sierra Madre Fault System (Figure 14) consists of three adjacent fault zones: the
San Fernando Fault Zone; the Sierra Madre Fault Zone; and the Cucamonga Fault Zone
(Southern California Earthquake Center, 2010). It is currently unclear if surface rupture can
propagate from one fault zone to another. Therefore, these three aforementioned reverse fault
zones, located at the southern edge of the San Gabriel Mountains, are considered a fault system
rather than a continuous fault zone (Southern California Earthquake Center, 2010).
The San Fernando Fault Zone, the westernmost of the three fault zones, is also the most
recent of the three fault zones to rupture. The 1971 Sylmar Earthquake (M 6.6) occurred along
what was then an unknown fault in the City of San Fernando and the Los Angeles neighborhood
of Sylmar (Figure 14) (Southern California Earthquake Center, 2010). Numerous buildings built
on top of the surface trace were subsequently demolished due to earthquake damage (Southern
California Earthquake Center, 2010). Trenching revealed recurrence intervals to be between
100-300 years, and expected magnitudes to be between M 6.0 – M 6.8 (Southern California
Earthquake Center, 2010).
The Sierra Madre Fault Zone, which runs through Altadena, Monrovia, and Glendora, is
a 55 km long fault zone often divided into five sections (Figure 14) (Southern California
Earthquake Center, 2010). The Sierra Madre Fault Zone is believed to be capable of generating
M 6.0 – M 7.0 earthquakes every several thousand years, although none have happened in recent
history.
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The easternmost fault zone, the Cucamonga Fault Zone, starts in Claremont, and passes
through Upland, Rancho Cucamonga, and Fontana (Figure 14) (Southern California Earthquake
Center, 2010). The probable magnitude remains the same as the Sierra Madre Fault Zone.
Figure 14. The Sierra Madre Fault System runs along the foothills of the Sierra Madre
Mountains. (Sources: U.S. Geological Survey and U.S. Census Bureau)
Earthquake Laws
As a response to the hundreds – or possibly thousands – of active faults in Southern
California, the state has some of the strictest building codes in the world. Due to property
destruction, losses of life and the subsequent hardships that California residents endure following
earthquakes, earthquake reform laws are often some of the most universally-supported, openlybipartisan laws anywhere. As a result of these laws, California has one of the best chances to
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survive a major earthquake out of any region on the planet. This section will discuss a few of
these laws and some potential issues which need to be addressed.
Field Act of 1933
Prior to March 10, 1933, the popular belief amongst engineers was that earthquakes could
only occur in rural areas (California Department of General Services, 2007). Schools at the time
were designed to withstand only wind loads (California Department of General Services, 2007).
The 1933 Long Beach Earthquake occurred on the evening of March 10 along the NewportInglewood Fault Zone, and wreaked havoc in Long Beach and Signal Hill (Southern California
Earthquake Center, 2007). This quake finally got the attention of engineers, public officials, and
the general public after 70 schools were destroyed and an additional 120 were damaged
(California Seismic Safety Commission, 1999). Buildings in the Golden State – in particular
schools and other public buildings – needed to be built to higher standards. Despite school not
being in session at the time of the quake, the great number of collapsed buildings led to a public
outcry about the safety of school buildings (California Department of General Services, 2007).
This was the reason the Field Act was passed only a month after the 1933 Long Beach
Earthquake (California Department of General Services, 2007).
The Field Act initially required that all building designs be based on building standards
adopted by the state (California Department of General Services, 2007). Plans and specifications
were also required from designers qualified by state registration (California Department of
General Services, 2007). The quality of any construction occurring within the state was to be
enforced through independent plan review and independent inspection (California Department of
General Services, 2007). Finally, architects, independent inspector, and the contractor had to
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verify under the threat of perjury that the building was constructed according to the approved
plans (California Department of General Services, 2007). However, it is important to note that
this law, as adopted, only applied to new construction. (California Department of General
Services, 2007).
Legislation to cover the criteria for continued use or abandonment of pre-1933 school
buildings was enacted under the Garrison Act of 1939 (California Department of General
Services, 2007). Most pre-Field Act buildings would be retrofitted to conform to then-current
building codes when funding became available in the 1970s. It is not a coincidence that funding
became available at this time; the 1971 Sylmar Earthquake brought the issue of school
construction back into the spotlight (California Department of General Services, 2007). In fact,
the 1971 Sylmar Earthquake caused the closure of Los Angeles’ first high school, which was
built in 1917 (Weinstein, 2010).
In the almost 80 years since the passage of the Field Act, no student or teacher has been
injured or killed due to the failure of a building from earthquakes, snow, wind, and other loads
(California Department of General Services, 2007). The Division of the State Architect (DSA),
the jurisdictional authority granted to oversee the plans and construction of school buildings,
undertook a study to determine cost differences between a school building in compliance with
the Field Act and a private school building constructed to the unamended code and enforced by
local jurisdictions. What they found was that the cost of construction only increased by less than
4% of the project cost. Less than 1.5% of the larger cost was associated with the stricter building
code (California Department of General Services, 2007).
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Alquist-Priolo Earthquake Fault Zoning Act
In 1972, Governor Ronald Reagan signed the Alquist-Priolo Special Studies Zone Act
(Earthquake Fault Zones were known as “Special Studies Zones” prior to January 1, 1994)
(California Geological Survey, 2007). Like the Field Act, this was a direct reaction to a
significant earthquake in Southern California: the 1971 Sylmar Earthquake (M 6.5) (California
Geological Survey, 2007). With this earthquake, extensive surface fault ruptures of a previously
unknown fault, the San Fernando Fault Zone, caused significant damage in the far northern San
Fernando Valley to numerous homes, commercial buildings, and other structures. Of all known
seismic hazards, fault rupture – when movement on a fault breaks to the surface and results in an
elongated, temporary crack on the ground where the surface trace of a fault is located – is the
most easily avoided hazard (California Geological Survey, 2007). The way to avoid it is simple:
do not build there.
The primary purpose of the Alquist-Priolo Earthquake Fault Zoning Act is to prevent the
construction of buildings for human occupancy on the surface traces of faults which are
“sufficiently active” (faults have displayed evidence of Holocene displacement, or within the last
11,000 years) and “well-defined” (trace can be found by a trained geologist) (Treiman, 2007).
Under the act, the State Geologist is required to establish regulatory zones around the surface
traces of active faults, known as Earthquake Fault Zones, and to issue appropriate maps where
the locations of active faults are either known or discovered in the future (California Geological
Survey, 2007). Earthquake Fault Zones are defined by turning points, identified by roads,
drainages, and other features on the ground, and connected by straight lines. The zones vary in
width, but average about ¼ miles (California Geological Survey, 2007).
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These maps are then distributed to all affected cities, counties, and state agencies for their
use in planning and controlling new or renewed construction (Figure 15). Unlike the Field Act,
which only requires the state to regulate school construction, local agencies must regulate most
construction projects within the zones (California Geological Survey, 2007). This allows local
jurisdictions to be more prohibitive than state law mandates. Before a project, such as the
construction of a new housing allotment, cities and counties must require a geologic
investigation to demonstrate that proposed buildings will not be constructed across active faults
(California Geological Survey, 2007). An evaluation and a written report of a proposed
construction site must be prepared by a certified geologist (California Geological Survey, 2007).
If an active fault is found, a structure for human occupancy has to be set back from the fault,
usually by about 50-100 feet (California Geological Survey, 2007). Occasionally, the maps have
to be subsequently revised based on geologic investigations, some coming from responses to
historic and modern earthquakes (Treiman, 2007). Many investigations which lead to
subsequent revisions are conducted as a direct result of an increase in development (Treiman,
2007). Revisions can be crucial, as many maps have been mapped inaccurately, and can depict
any given Earthquake Fault Zone as being in the wrong location (Treiman, 2007).
The Alquist-Priolo Earthquake Fault Zoning Act does not apply to buildings built upon
surface fault traces before 1972 (California Geological Survey, 2007). One weakness of this act
upon its passage was that potential buyers of homes, especially of those in more antiquated areas
on fault zones such as Santa Barbara and Old Town Temecula, were not required by state law to
be notified about the presence of surface fault traces on or near the property (California
Geological Survey, 2007). This was not corrected until 1998, when the Natural Hazards
Disclosure Act was passed (California Geological Survey, 2007). Another weakness is that the
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act only pertains to fault rupture. Other earthquake hazards were not to be addressed until 1990,
when the Seismic Hazards Mapping Act was passed.
Seismic Hazards Mapping Act
While the Alquist-Priolo Earthquake Fault Zoning Act was a significant step in reducing
the threat posed by earthquakes in California, it merely focused on a minor seismic hazard, a
surface rupture. Most of the economic losses in earthquakes are a result of liquefaction,
amplified ground shaking, and earthquake-induced landslides (California Department of
Conservation, 2007). The hazards were not addressed in California law until October 17, 1989,
when the 1989 Loma Prieta Earthquake (M 6.9) struck the San Francisco Bay Area (California
Department of Conservation, 2007). While the focus of the earthquake was deep under the Santa
Cruz Mountains, most of the damage was inflicted upon structures along the waterfronts of San
Francisco and Oakland. Liquefaction caused fires and even collapses in these areas, including
Oakland’s double-decker Cypress Viaduct (California Department of Conservation, 2007). The
aftermath of this quake was the catalyst for the passage of the Seismic Hazards Mapping Act in
1990 (California Department of Conservation, 2007).
The primary function of the Seismic Hazard Mapping Act is to create maps delineating
zones, much like the Alquist-Priolo Earthquake Fault Zoning Act, where data suggest amplified
ground shaking, liquefaction, earthquake-induced landslides, or other seismic hazards caused by
earthquakes may occur (Figure 15) (California Department of Conservation, 2007). These areas
would be known simply as “seismic hazard zones”. It is important to note that not every
earthquake will trigger liquefaction and/or landslides in these locations. In a 2004 update to the
seismic hazard zone mapping guidelines, an advisory board decided that amplified ground
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motion was sufficiently addressed by the 2001 California Building Code. Consequently, the
State Geologist does not map zones for this hazard (California Department of Conservation,
2007).
The Seismic Hazard Mapping Act requires agencies to approve projects only following
an investigation of the site to detect if the hazard is present. Furthermore, if the danger is
detected on the site, appropriate mitigations must also be included (if possible) (California
Department of Conservation, 2007). This act also requires real estate sellers and agents to
disclose at the time of sale if a property is within a seismic hazard zone, making this the first act
in California to require disclosure of proximity to seismic hazards (California Department of
Conservation, 2007). Like the Alquist-Priolo Earthquake Fault Zoning Act, the Seismic Hazards
Mapping Act allows local jurisdiction to make decisions on seismic hazards zones which are
stricter than what state law requires (California Department of Conservation, 2007).
Natural Hazards Disclosure Act
The Natural Hazards Disclosure Act was passed in 1998 to require that sellers of
California properties and their respective agents provide potential buyers with a “Natural Hazard
Disclosure Statement” – a statement disclosing that a property lies within one or more statemapped hazard areas, such as fault zones or earthquake-induced landslide regions (California
Department of Conservation, 2007). The act specifies two ways in which this mandated
disclosure can be made. The first is to use the new Natural Hazards Disclosure Statement. The
second is to utilize the Local Option Real Estate Disclosure Statement, which can only be used if
the Local Option Statement contains the same information and the same warning as does the
Natural Hazards Disclosure Statement (California Department of Conservation, 2007). In
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addition to Seismic Hazard Zones, official maps of Earthquake Fault Zones and other natural
hazard maps, both state and federal, must also be disclosed (California Department of
Conservation, 2007).
As of August 16, 2010, there are official maps of Seismic Hazard Zones affecting parts of
eight counties and over 200 cities (Figure 15) (California Department of Conservation, 2007). In
Southern California, if a property is within Los Angeles, Orange, San Bernardino, or Ventura
Counties, the list of affected cities must be consulted. If one’s city of choice is listed, the
detailed maps, which use California Geological Survey’s 7.5 minute quadrangles, must then be
compared with local street maps or parcel maps. However, if one’s city is outside of these
counties, then maps will be made available as time progresses. Some populous counties in
Southern California without any available official maps of Seismic Hazard Zones include
Riverside, San Diego, and Kern Counties, whose combined population exceeds 5,000,000;
furthermore, only Chino Hills is covered in San Bernardino County, leaving an additional
2,000,000 people in the county without coverage (California Department of Conservation, 2007).
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Figure 15. An example of an official map of a Seismic Hazard Zone. This map is of the
Hayward Fault Zone in Fremont, located near Oakland. (Source: California Department
of Conservation)
Room for Improvement
While the past 80 years have seen much progress in the area of earthquake safety, there is
still much Californians can do to further increase the odds of surviving the next major
earthquake. However, it is important to note that buildings are not always going to be invincible,
even if they are away from mapped fault traces, liquefaction, seismically-induced landslides, etc.
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Buildings today might be able to better withstand earthquakes, but that does not guarantee a
building’s survival. Therefore, it is important to give any given building the best possible chance
for surviving by having inspections performed on buildings annually or semi-annually.
While seismically-induced building collapses might be able to be prevented in the future
via an improvement in technology, changing some clauses in current California earthquake law
could lead to a significant improvement in overall safety during the next major earthquake. For
instance, the Alquist-Priolo Earthquake Fault Zoning Act only applies to buildings constructed
before 1972. There are a couple of unique ways this problem could be remedied.
The first idea would be to discourage home purchases inside of designated fault zones by
artificially inflating the prices of buildings there by adding a significant tax – no more than 25%
of the appraised value of the home –, with the tax revenues being split between municipalities,
counties, and the state. This would encourage the construction of buildings outside of designated
fault zones using the free market and demand for affordable housing, hopefully causing realtors,
buyers, and builders to build away from fault zones yet close to central business districts. If
buildings are unable to be sold to homebuyers after an extended period of time due to the high
asking prices, then they would be demolished. The second idea requires far more capital, but is
more likely to succeed. This idea would mandate government buyouts of buildings located in
mapped fault zones. Owners of these buildings would be given market value for their property,
and would then be able to relocate to another building of equal or lesser value outside of mapped
fault zones. The flaw with this idea is that in order to perform it well, money must be abundant.
It is clearly not the case, with California being on the verge of bankruptcy and Orange County
recently emerging from bankruptcy itself. Once the demolitions (as with Idea 1) or buyouts (as
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with Idea 2) are completed, zoning codes could be amended to include all mapped fault zones as
open space and/or parkland, thus preventing development on these zones of weakness.
An Analysis of Southern California Zoning Codes
Zoning codes are visions of what an area (not necessarily a city) will look like and how it
will function. Planners often ask themselves as well as the general public which qualities they
would like their study areas (often the cities they work for) to possess in the near and/or distant
future, as well as analyzing the negative qualities their respective study areas possess in the
present. While natural hazards might be far more prevalent in Southern California than in most
other places nationwide, that does not prevent developers from intending to construct in ill
advised areas. As a planner, it is their job to regulate which building types will be constructed
where, hopefully preventing hospitals from being built on top of the San Andreas Fault Zone or
apartment complexes from being built next to fire-ravaged mountainsides susceptible to
landslides. This section will not only look at zoning codes for several municipalities of all sizes
in Southern California; it will also judge the planners in charge of these plans to see if their
zoning codes encourage developing in dangerous locations or discourage that. It is important to
note that light residential zoning along a fault trace does not guarantee that a house will be
situated on a mapped fault trace; many of these zoning codes are for rapidly-growing
municipalities whose populations exploded after the passage of the Alquist-Priolo Earthquake
Fault Zoning Act.
Most of the information used in this section is contained in General Plans. A General
Plan is supposed to be amended every ten years, but often isn’t. General Plans consist of seven
“elements”. The two elements of the General Plan this section will use most extensively are the
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one pertaining to environmental hazards (e.g., fault zones and liquefaction zones) and the one
pertaining to community development, where the zoning codes are often discussed extensively.
Methodology
For this analysis, a rubric was created featuring four categories, with each category rating
six municipalities’ General Plans and how well they prepare their respective municipalities for
earthquakes. These four threats – fault rupture, liquefaction, earthquake-induced landslides, and
other earthquake-related threats, such as tsunami or earthquake-induced wildfires – were taken
directly from California earthquake laws, as explained in earlier portions of this report. Next, all
four threats were given scores based off of how well these risks are averted, with 4 being the
highest possible score and 0 being the lowest possible score in each category, meaning that 16
points are possible.
The six municipalities selected were chosen out of a convenience sample (Figure 16).
These municipalities each have different soil compositions, different populations, and each face
different risks, thus making evaluating how well they are prepared a subjective process. While
the scores could vary if different people were evaluating these municipalities using the same
rubric (albeit insignificantly), it is important to note that the rubric is based on information
contained in the General Plans themselves.
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Figure 16. Locations of cities whose General Plans were critiqued. (Source: U.S. Census
Bureau)
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Banning
Banning is a city of 27,851 people in north-central Riverside County, located between the
urbanized area of Los Angeles-Santa Ana-Riverside and the urbanized area of Indio-Palm
Springs (Census Bureau, 2010). Its location in the San Gorgonio Pass and near the junction of
the San Andreas Fault and the Banning Fault/San Gorgonio Thrust puts Banning in a rather
precarious situation: Should they promote growth or promote public safety?
Banning’s zoning code is unique in that open space designations are utilized to cover
Seismic Hazard Zones (City of Banning, 2006). In the extreme eastern portion of the city, an
unnamed fault is covered by the designation Open Space – Resources (Figures 18 & 19). The
rural northern half of the city hosts numerous faults, including the Gandy Ranch Fault, the San
Andreas Fault, the Mission Creek Fault, and the Banning Fault (Figure 18). Open Space –
Resources is a common zoning type up here, as are very low density rural zoning types,
including Ranch/Agriculture and Rural Residential (Figure 19) (City of Banning, 2006). The
southernmost mapped fault zone within city limits, the San Gorgonio Thrust, raises the most
concern. The fault zone passes through Low Density Residential zoning, posing a minor risk
along this City of Banning Hazard Management Zone, the local equivalent of the Alquist-Priolo
Earthquake Fault Zoning Act (Figures 18 & 19) (City of Banning, 2006). This is important, as
the Alquist-Priolo Act has not mapped the Banning area yet (City of Banning, 2006).
Banning is prone to wildfires, with a few over the past century coming less than ½ mile
from the urban core of Banning (City of Banning, 2006). This fact lowers Banning’s rating for
other hazards. Liquefaction in the General Plan is addressed, despite a low-to-medium
probability for it occurring here. However, geologic investigations are only suggested here.
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Investigations are mandatory for construction on steep slopes, many of which align fault traces.
Due to the rapid growth of Banning and its unstable geologic location, geologic investigations
need to be mandated at all times.
Score: 75%
Figure 17. The rubric used to critique Banning’s General Plan.
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Figure 18. Faults located in Banning. (Source: City of Banning)
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Figure 19. Banning’s General Plan Land Use Map. (Source: City of Banning)
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Costa Mesa
Costa Mesa is a city in south central Orange County, and occupies a significant portion of
one of the largest edge cities in the county, South Coast Metro (part of South Coast Metro also
lies within Santa Ana city limits). With a population of 105,928, it would qualify as a boomburb
– a suburb with a population over 100,000 with few urban characteristics 30-50 years ago
(Census Bureau, 2010). While the dominant strand of the Newport-Inglewood Fault Zone is
outside of city limits, multiple minor strands terminate within the city near Upper Newport Bay.
Developments away from South Coast Metro often obscure the surface traces of faults in
Costa Mesa, which generally have a west-northwest to east-southeast orientation and are all
greater than a mile away from Interstate 405 and California Route 73, making them closer to the
cultural core of the city (City of Costa Mesa, 2002). However, some of the city’s largest least
intensive properties are also along the fault traces. For instance, Orange County Fairgrounds,
Fairview Park, and Orange Coast College are all on top of minor strands of the NewportInglewood Fault Zone. These same faults also skim the edges of Costa Mesa City Hall,
Vanguard University and other schools, as well as Fairview State Hospital (Figure 21) (City of
Costa Mesa, 2002). Moderate densities are also found on top of these faults, which are not
Alquist-Priolo Earthquake Fault Zones. Light Industrial, Light Residential, Medium Residential,
and Commercial Residential are all penetrated by these fault strands (Figures 21 & 22) (City of
Costa Mesa, 2002). The one thing perhaps increasing their rating is the uncertainty with which
the faults are mapped in. The faults are all in straight lines, and seem to be inferred (Figure 21)
(City of Costa Mesa, 2002). However, it is unknown if faults within city limits can produce
surface ruptures; the nearest fault that can do that is the Newport-Inglewood Fault Zone, located
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¾ mile outside city limits (City of Costa Mesa, 2002). Finally, liquefaction also plays a role in
locations of buildings, but few buildings appear to be impacted in Costa Mesa.
Score: 81% if faults within city limits can produce surface ruptures; 100% if faults within city
limits are unable to produce surface ruptures
Figure 20. The rubric used to critique Costa Mesa’s General Plan.
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Figure 21. An estimated fault map of Costa Mesa. (Source: City of Costa Mesa)
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Figure 22. Costa Mesa’s General Plan Land Use Map.
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Desert Hot Springs
Ironically, Desert Hot Springs owes its very existence to the Mission Creek Fault, part of
the San Andreas Fault Zone. The Mission Creek Fault, like other faults throughout the arid
Coachella Valley with a surface trace, forces groundwater to rise to the surface, forming linear
oases in an otherwise barren desert. As a result of this phenomenon, spas developed along the
fault trace, leading to urbanization in the area (City of Desert Hot Springs, 2000). 22,537
residents call Desert Hot Springs home, making it one of the fastest-growing suburbs in the
Coachella Valley (Census Bureau, 2010). Desert Hot Springs is located north-northwest of Palm
Springs in Riverside County, making it the northernmost city in the Coachella Valley.
The Mission Creek Fault runs through the southwestern part of Downtown Desert Hot
Springs, which right there is already making the planning here rather ill advised (Figure 24) (City
of Desert Hot Springs, 2000). Downtown has buildings which predate the Alquist-Priolo
Earthquake Fault Zoning Act. As a result, the General Plan seems to indicate that Desert Hot
Springs is more interested in preserving historic structures in downtown, as indicated by their
zoning code lacking Open Space designations along the fault trace (City of Desert Hot Springs,
2000). In fact, Medium Residential, Light Residential, and General Commercial are the
predominant zoning types along the fault trace (Figures 24 & 25) (City of Desert Hot Springs,
2000). In newer developments, though, the street layout would indicate that the developers are
respecting the potential for disaster the Mission Creek Fault, which is overdue for a major
earthquake, presents to residents. While it is not specifically zoned as Open Space, it is apparent
that it is being treated as such due to the street grid (Figures 24 & 25) (City of Desert Hot
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Springs, 2000). On the outskirts of town, landslides are a threat, although the probability of
landslides affecting the urban core is non-existent due to the flat slope. Downtown Desert Hot
Springs’ emphasis on preserving historic downtown buildings within the fault zone places many
lives in danger.
Score: 75%
Figure 23. The rubric used to critique Desert Hot Springs’ General Plan.
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Figure 24. Faults near Desert Hot Springs. (Source: City of Desert Hot Springs)
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Figure 25. Desert Hot Springs’ General Plan Land Use Map. (Source: City of Desert Hot
Springs)
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Fontana
Fontana, most famously home to the Pepsi MAX 400 at Auto Club Speedway, is already
a fairly large city in its own right. With a population of 186,642, Fontana is poised to become
the most populous city in San Bernardino County (Census Bureau, 2010). Its location in the
west-central San Bernardino Valley of southwestern San Bernardino County would give a city
which would otherwise be a central city in many metropolitan areas the status of a boomburb.
Fontana’s northern boundary roughly follows the Cucamonga Fault Zone, while the RialtoColton Fault and the San Jacinto Fault Zone also run through the city (Figure 27) (City of
Fontana, 2003).
The Cucamonga Fault Zone is entirely overlaid by Open Space zoning types, so no
problems are found there (Figures 27 & 28) (City of Fontana, 2003). However, the first gas
stations on Interstate 15 after descending Cajon Pass are very near the San Jacinto Fault Zone.
These gas stations probably do not lie within the fault zone, though; they appear recently
constructed, thus eliminating the possibility that they predate 1972 (City of Fontana, 2003).
While the Rialto-Colton Fault is the least active of those listed within Fontana city limits,
the Rialto-Colton Fault skims the outer edge of development surrounding Downtown Fontana,
primarily being located under Light Residential/Ranch zoning types (Figures 27 & 28) (City of
Fontana, 2003). It is here where the population is expected to grow exponentially. However, the
Rialto-Colton Fault is not an Alquist-Priolo fault, and is primarily a groundwater barrier within
city limits (City of Fontana, 2003). It is currently unclear whether this fault, as well as other
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inferred faults within city limits, are capable of producing damaging earthquakes (City of
Fontana, 2003).
Fontana’s status as a growing town gives it the distinction of being able to fully comply
with earthquake laws as they are expanding. Thus, the only concern about Fontana’s General
Plan is what actions will be done to mitigate the dangers presented by the Rialto-Colton Fault
and other inferred faults if further research indicates that large earthquake have occurred here in
the past.
Score: 100%
Figure 26. The rubric used to critique Fontana’s General Plan.
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Figure 27. Faults within the City of Fontana. (Source: City of Fontana)
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Figure 28. Fontana’s General Plan Land Use Plan Map. (Source: City of Fontana)
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Hemet
Hemet is a medium-sized suburb with a rural character, making it the perfect filming
location for such movies as Seabiscuit and The Fast and the Furious. The widening of
California Route 74 west of town as spurred growth in the San Jacinto Valley – actually a
misnomer, as the valley is actually a graben formed by the Casa Loma Fault and the Claremont
Fault, both strands within the San Jacinto Fault Zone (City of Hemet, 1992). Its population of
75,163 would place it amongst the larger cities of Riverside County (Census Bureau, 2010).
With hills and mountains surrounding the city on three sides, such scenery could only be caused
by cataclysmic events; in fact, earthquakes on Christmas Day, 1899 and Easter Sunday, 1918
both destroyed Hemet and neighboring San Jacinto (Southern California Earthquake Center,
2010). This makes Hemet a risky location to rebuild a city, let alone expand.
Unlike most cities, which were founded where their downtowns are and build out in all
directions, Hemet started out in their downtown and grew rapidly to its west, as well as the
southwest . The reason Hemet only grew rapidly to the north along State Street and grew only
marginally to the east was the presence of the Casa Loma and Park Hill Faults (Figure 30) (City
of Hemet, 1992). The two strands are below primarily R-5 and R-8 zoning – both Low and
Medium Density Residential (Figure 30) (Hemet General Plan, 2007). However, underneath the
two largest commercial districts on the north and east sides of Hemet, State Street and Florida
Avenue, Community Commercial and Mixed Use can be found (Figure 30) (Hemet General
Plan, 2007). The zoning code appears not to zone fault zones as Open Space; however, buildings
within the fault zone have been torn down in some locations, especially along Florida Avenue
(Figure 30) (Hemet General Plan, 2007). Liquefaction is a moderate threat for a majority of the
city (City of Hemet, 1992). However, the biggest threat to Hemet is earthquake-induced
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landslides. Hemet city limits include Tres Cerritos, the Lakeview Mountains, and Park Hill, all
of which are capable of massive landslides which could destroy properties in the area (City of
Hemet, 1992). Tahquitz High School even decided to build their campus and football stadium
into Tres Cerritos, a series of steep hills west of the Casa Loma Fault. Hemet has progress to
make with its zoning code.
Score: 63%
Figure 29. The rubric used to critique Hemet’s General Plan.
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Claremont
Fault
Casa Loma
Fault
Park Hill
Fault
Clark Fault
Figure 30. Hemet’s General Plan Land Use Map, overlaid with fault zones in Hemet.
(Sources: City of Hemet and Hemet General Plan)
Seal Beach
Seal Beach is Long Beach’s southeastern neighbor on the other side of the San Gabriel
River. Located in Orange County, Seal Beach is a modestly-sized city, with a population of
24,485 (Census Bureau, 2010). Within city limits are the Naval Station at Seal Beach and the
Anaheim Bay National Wildlife Refuge, which occupy over half of the city’s land (City of Seal
Beach, 2003). The wildlife refuge is marshy the same reason Desert Hot Springs is an oasis; the
Newport-Inglewood Fault Zone rushes water up to the surface, creating a large saltwater marsh
between Long Beach and Huntington Beach (City of Seal Beach, 2003).
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The Newport-Inglewood Fault Zone has one mapped strand throughout city limits
(Figure 32). While most of it meanders through marshes and the Naval Station, it runs
dangerously close to Low Density Residential (Figures 32 & 33) (City of Seal Beach, 2003).
The fault zone itself is zoned as Open Space throughout this stretch, making it only a danger to
the Naval Base (Figures 32 & 33). Liquefaction would be the biggest concern in Seal Beach,
with ground shaking not being far behind. The map depicted in the General Plan shows the
entire city is at risk for significant liquefaction (City of Seal Beach, 2003). The Plan also
indicates that the city would receive induced shaking as a result of the city’s location in an
alluvial fan, although buildings complying with the 2001 California Building Code should
withstand a major quake along the Newport-Inglewood Fault Zone or elsewhere (City of Seal
Beach, 2003). However, both these problems are addressed with mandating mitigation where
possible, as well as requiring thorough geologic investigations for new construction. Tsunami
remain a threat here, primarily from subduction zones in Chile and Japan. While some attention
is given to saving lives during a tsunami, most of the attention was redirected towards earthquake
safety. A more comprehensive plan to evacuate in the event of a tsunami would give Seal Beach
a perfect score in its rubric.
Score: 88%
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Figure 31. The rubric used to critique Seal Beach’s General Plan.
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Figure 32. Fault Zone Map for Seal Beach. (Source: City of Seal Beach)
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Figure 33. Land Use Map for the City of Seal Beach. (Source: City of Seal Beach)
Overview
While some areas are beginning to zone with respect to fault zones (e.g., including
surface traces of faults and steep slopes as Open Space, building with caution in liquefaction
zones, etc.), most appear to be using the state requirements for building construction in fault
zones. Some municipalities seemed to benefit from having excellent locations, such as Fontana,
while others appear to be in questionable locations but are limiting intensive development to
fault-free areas, such as Banning. While the sample shown here is only a very small portion of
all General Plans available in Southern California, these each have similarities which can be used
to draw conclusions about most municipalities. First, liquefaction appears to be a very serious
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threat. As most buildings have been constructed so as not to mitigate the threat posed by
liquefaction, municipalities with higher water tables need to consider geologic investigations in
high-threat liquefaction zones prior to new construction. Second, if the Alquist-Priolo
Earthquake Fault Zoning Act and other similar municipal and county hazard zones did not
prevent new construction in fault zones, fault rupture would be a major issue. It is unclear
whether all six cities used municipal and county hazard zones in their General Plans, so cities
with uncertain locations of faults, such as Costa Mesa, should be vigilant in investigating faults
within city limits.
Conclusion
This study demonstrates that many communities in Southern California are at great risk.
With many of these faults lying under urbanized areas, it is crucial that communities take further
actions to prevent extensive property damage and loss of life. Perhaps advancements in the field
of earthquake engineering will reduce the danger that liquefaction and ground shaking pose to
structures. However, earthquakes do not strike when it is most convenient for society; they
occur randomly along preexisting zones of weakness that may or may not be mapped. As such,
existing buildings should be retrofitted as soon as possible.
If a catastrophic earthquake were to happen today, it is very likely that the number of
casualties would surpass any other disaster in American history. This is the result of poor
planning, although more municipalities are correcting the mistakes of the past. Better planning
would not make the next major earthquake casualty-free. It would significantly reduce how
many casualties occur and how many structures are significantly damaged and destroyed. The
1989 Loma Prieta Earthquake demonstrated that buildings on loose, unconsolidated sediment
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have a much lesser chance of surviving an earthquake than buildings anchored into bedrock.
Finding ways to either lower groundwater levels or finding ways to mitigate this danger could
lessen the risk faced by entire cities, in some cases.
In other cases, structures and their inhabitants are threatened by surface traces of faults.
Due to loopholes in crucial earthquake laws, it is legal in some cases for residents to maintain
homes on top of faults. Closing this loophole will be a financial burden on the state, as well as
municipalities and their respective counties. Creative solutions are needed to solve this
complicated issue before additional development occurs or a significant earthquake causes large
loss of life and property.
A secondary issue compared to the strict enforcement of earthquake laws, zoning codes
with Open Space or Agricultural zoning types would effectively discourage businesses and
residents from living in fault zones. While the increase in parkland and/or trails would satisfy
residents, such a zoning change would also serve as a mechanism to protect inhabitants along
fault zones.
The final message this report will give is not one of gloom and doom, but one of hope
and promise. The pieces are falling together rapidly for Southern California. By the end of the
21st century, there is a good probability Southern California will be close to earthquake-resistant
due to the speed of progress in the field of earthquake engineering, as well as improvements in
earthquake planning. Every resident must do his or her part to make this dream become a reality,
even if it is expensive.
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