General Plan Update - City of Inglewood

Chapter 6 Community Safety and Hazards
earthquake. The moment magnitude of an earthquake is defined relative to the seismic
moment for that event.
Earthquake intensity in a given locality is typically measured using the Modified Mercalli
Intensity Scale with values of this scale ranging from I to XII. The most commonly used
adaptation covers the range of intensities from the conditions of a value of I that is
defined as not felt except by very few, favorably situated, to XII that is defined as damage
total, lines of sight disturbed, and objects thrown into the air. While an earthquake has
only one magnitude, it can have many intensities, which typically decreases with distance
from the epicenter. See Table 6.2-1 for more information on the Modified Mercalli
Intensity Scale.
Faults
The Southern California region is seismically active and commonly experiences strong
groundshaking resulting from earthquakes along both known and previously unknown
active faults. Active faults are defined as faults that have caused soil and strata
displacement within the Holocene period (the last 10,000 years). Potentially active faults
are faults that have experienced movement in the Quaternary period (last two million
years), but not during the Holocene. Faults that have not experienced movement in the
last two million years are generally considered inactive.
The City of Inglewood contains both active and potentially active faults. Figure 6.2-1
illustrates the locations of regional faults and fault zones within the City and surrounding
areas.
The Newport-Inglewood Fault Zone (NIFZ), sometimes referred to as the Newport
Inglewood Zone of Deformation, is a zone of discontinuous folds and faults which
stretch across the Los Angeles basin in a northwest-southeast direction from Beverly
Hills to Newport Beach. The deformation along NIFZ has been caused by displacement
in the basement rocks and the overlying 10,000 to 12,000 feet of softer Tertiary and
Quaternary sediments. The marine and continental sedimentary rocks have been warped
and faulted forming such hills as the Baldwin, Rosecrans, and Dominguez. Thus, the hills
are judged to be very young. This structural zone is exemplified by the young age of
sedimentary rocks involved in the deformation, the observed regional and local changes
in surface elevation along and across the zone, and the abundance of earthquake
epicenters over the last 60 years closely associated with this zone. This deformation is
considered presently and potentially active.
In addition to the NIFZ, several additional active or potentially active faults are located in
or nearby the City. The Newport-Inglewood fault extends through the City and runs
parallel to the San Andreas system and lies partly under the Pacific Ocean. Several
moderate earthquakes and numerous smaller shocks have been recorded in proximity to
the Newport-Inglewood zone and have originated on the deeper faults within the zone.
The Inglewood Fault, one component of the Newport-Inglewood fault, has been mapped
6.2-2
City of Inglewood General Plan Update Technical Background Report