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4.6 GEOLOGIC AND SEISMIC HAZARDS

Cypress General Plan EIR




FINAL
4.6-1
Geologic and Seismic Hazards
4.6
GEOLOGIC AND SEISMIC HAZARDS

This Section describes the current conditions relating to the geologic and seismic characteristics of the
City of Cypress. This Section concludes with an analysis of geologic and seismic impacts associated
with implementation of the proposed General Plan Update.

4.6.1 ENVIRONMENTAL
SETTING

GEOLOGY

Cypress is composed of quaternary deposits of alluvium and colluvium. Alluvium results from
sediments deposited from running water and colluvium forms as rock fragments and soil material
accumulate at the base of steep slopes.

Cypress geologic structure does not include any active or potentially active faults. The City is,
however, located in a seismically active region. The following five faults lie within close proximity to
Cypress: Norwalk, El Modena, Whittier-Elsinore, Elysian, and Newport-Inglewood. In addition to these
faults, the San Andreas Fault is situated approximately 45 miles north of Cypress. The San Andreas
Fault is anticipated to deliver up to an 8.3 earthquake within the next thirty years.

SOILS

The following discussion is based on information contained in the Soil Survey of Orange County and
Western Part of Riverside County conducted by the U.S. Soil Conservation Service. The U.S. Soil
Conservation Service identifies a number of soils in Cypress. These soils include the San Emigdio
Series, Metz Series, Hueneme Series and Bolsa Series, all of which are suitable for urban development
(see Exhibit 4.6-1, Soils Map).

San Emigdio Series. These soils are found throughout the northern and central portions of Cypress.
They are nearly level and consist of well-drained soils on floodplains and alluvial fans.

Metz Series. These soils are also nearly level. They include somewhat excessively drained sands on
alluvial fans and flood plains. They are predominantly located in northeastern Cypress.

Hueneme Series. This series consists of poorly drained soils on alluvial fans and floodplains, which are
located in northern Cypress.

Bolsa Series. The Bolsa Series consists of somewhat poorly drained soils on alluvial fans. These soils
are situated in southern Cypress near the Los Alamitos Race Track and Cypress Golf Course.


AGRICULTURE PRODUCTION RESOURCES

Cypress was originally an agriculture and dairy community, featuring row crops and citrus trees.
However, like much of Orange County, Cypress developed rapidly during the 1960s and 1970s, and
agricultural acreages were converted to urban uses. A few row crops (predominantly strawberries)
remain in southern Cypress. This land is, however, planned and zoned for business park development.

MINERAL RESOURCES

The State Division of Mines and Geology identifies mineral resource areas throughout the State.
According to the Geologic Map of Orange County showing Mines and Mineral Deposits, Cypress does
not contain any mineral resources. Cypress General Plan EIR




Geologic and Seismic Hazards

4.6-2
FINAL

Insert Exhibit 4.6-1, Soils Map


Cypress General Plan EIR




FINAL
4.6-3
Geologic and Seismic Hazards
SEISMIC HAZARDS

The following section describes the presence and characteristics of seismic hazards in Cypress,
including earthquake faults, surface rupture, ground shaking, liquefaction, hazardous buildings, and
seismic response.

EARTHQUAKE FAULTS

While no active or potentially active faults are located within the City of Cypress, the entire Southern
California region is considered to be seismically active. Five faults are situated within close proximity to
Cypress: Newport-Inglewood, Norwalk, El Modena, Whittier-Elsinore, and Elysian Park. The San
Andreas and San Jacinto faults are located further from Cypress than these five faults, but have the
potential to deliver larger magnitude earthquakes. Exhibit 4.6-2, Regional Fault Map, depicts these
faults.

Newport-Inglewood Fault. The Newport-Inglewood fault zone is a series of echelon
northwest-trending and vertically-dipping faults extending from the southern edge of the Santa Monica
Mountains southeastward to the offshore area near Newport Beach. From north to south, the fault
segments are:

Charnock
Fault;
Overland Avenue Fault;
Inglewood
Fault;
Potrero
Fault;
Avalon-Compton
Fault;
Cherry Hill Fault; and
Seal Beach Fault.

Numerous shocks of 4.0 magnitude or greater, as well as the historic 6.3 magnitude Long Beach
Earthquake in March 1933, have been generated within this fault zone and suggest an active seismic
history. Although there has been no observed ground displacement associated with the
Newport-Inglewood Fault Zone, there may have been subsurface fault displacement of approximately
seven inches associated with the October 21, 1941, and June 18, 1944, earthquakes. This fault zone
could generate a 7.6-plus magnitude maximum credible earthquake.

Norwalk Fault. The Norwalk Fault is approximately 16 miles long and lies approximately five miles
north of Cypress. Seismic activity has occurred along this fault.

El Modena Fault. The El Modena Fault is a north trending fault located approximately 10 miles north
of Cypress. Evidence suggests that the fault was active at one time; however, the fault is now thought
to be inactive.

Whittier-Elsinore Fault. The Whittier-Elsinore Fault is situated approximately 10 to 12 miles north of
the City. There have been several minor earthquakes along this fault. Seismic history reveals that the
fault is able to produce a seismic event of magnitude 6.0 or greater.

Elysian Park Fault. The Elysian Park Fault is located approximately 15 to 20 miles north of the City in
the Montebello and Monterey Park areas. The Elysian Park Fault produced the 1987 Whittier Narrows
5.9 magnitude earthquake. Cypress General Plan EIR




Geologic and Seismic Hazards

4.6-4
FINAL

Insert Exhibit 4.6-2, Regional Fault Map



Cypress General Plan EIR




FINAL
4.6-5
Geologic and Seismic Hazards
San Andreas Fault. The San Andreas Fault extends over 600 miles, encompassing virtually the entire
length of California. The fault is divided into segments that have somewhat distinctive behavior
patterns. The southern segment is over 300 miles long and occasionally delivers large earthquakes.
The San Andreas is located approximately 60 miles north of the City of Cypress.

The last great earthquake on this segment was the 1857 Fort Tejon earthquake that is believed to have
caused a rupture extending 200 miles. Several other earthquakes have been attributed to the San
Andreas Fault; the last one to affect Southern California was a 6.7 magnitude quake in 1899. It is
estimated by geologists that this fault may have the potential to generate an earthquake of magnitude
8.5 on the Richter scale, which is designated as the maximum credible earthquake.

San Jacinto Fault. The San Jacinto Fault branches from the San Andreas Fault on the north side of
the San Gabriel Mountains and parallels the San Andreas to the Mexico-California border. This fault is
located approximately 40 miles north of Cypress. The San Jacinto fault has been very active, and
damaging earthquakes have occurred along its entire length. The last earthquake on this fault
exceeding 6.0 occurred in 1968. Ten damaging earthquakes have been attributed to this fault since the
1800s, ranging from 5.4 to 6.8 on the Richter scale.

SURFACE RUPTURE AND GROUND SHAKING

Surface rupture resulting from earthquakes is unlikely to occur in Cypress as no faults have been
identified within the City boundaries. The nearest active faults, the El Modena and Norwalk Faults, lie
approximately five to ten miles north of Cypress. Other faults located outside the Cypress area include
the Newport Inglewood, Whittier-Elsinore, Elysian Park, San Jacinto, and San Andreas.

The future impact of earthquakes on Cypress depends on several factors. The particular fault, fault
location, distance from the City, and magnitude of the earthquake all determine the degree of shaking
that will occur in the City. In addition, the soil and geologic structure underlying Cypress influences the
amount of damage that the City may experience. The soils underlying Cypress include alluvium
deposits that may become unstable during intense groundshaking.

The Newport-Inglewood Fault is anticipated to generate the most destructive ground shaking in
Cypress. The El Modena and Norwalk Faults, though closer to the City, are predicted to generate
smaller magnitude earthquakes. The San Jacinto Fault is very active and has historically produced 6.0
to 7.0 earthquakes. However, as Cypress lies approximately 40 miles to the south, the distance
b