General Plan Update - City of Inglewood

6.2 Seismic Hazards
6.2 SEISMIC HAZARDS
The City of Inglewood is in a seismically active region of Southern California. This
section describes regional faulting, historical seismic activity in the surrounding area,
groundshaking, and other seismic and geologic hazards that could affect the City.
Information obtained in this section is based on the General Plan Safety Element, the
Hazard Mitigation Plan, and previous environmental documentation prepared for the
City. Full bibliographic references are provided at the end of this section.
• Existing Conditions
Regional Geology
The City of Inglewood is located within the Los Angeles basin area, at the southern edge
of the Transverse Ranges geomorphic province, and near the northern boundary of the
Peninsular Ranges geomorphic province (Yerkes et al. 1965). Most of the Transverse
Ranges province is mountainous, including the San Gabriel and San Bernardino
mountains to the east, and the Santa Monica Mountains to the north. The Peninsular
Ranges geomorphic province is characterized by a series of northwest/southwesttrending
mountains, including the San Jacinto and Santa Rosa mountains, and faults
including the Newport-Inglewood Fault and the Whittier-Elsinore Fault. The San
Andreas Fault is located approximately 45 miles northeast of Inglewood.
Most of the City is underlain by a thick (10,000 to 12,000 foot) section of Tertiary and
Quaternary marine and continental sedimentary rocks deposited on an igneousmetamorphic
basement complex. The Tertiary rocks, consisting primarily of sandstone,
silt-stone, and shale, are almost entirely of maring origin and range in age from Eocene to
Pliocene. The Quaternary rocks consist of shallow marine sandstone and siltstone as well
as continental siltstone, mudstone, and gravel.
Faulting
Earthquake magnitude is a quantitative measure of the strength of an earthquake or the
strain energy released by it, as determined by the seismographic or geologic observations.
It does not vary with distance or the underlying earth material. This differs from
earthquake intensity, which is a qualitative measure of the effects a given earthquake has
on people, structures, loose objects, and the ground at a specific location. Intensity
generally increases with increasing magnitude and in areas underlain by unconsolidated
materials, and decreases with distance from the epicenter.
Several magnitude scales have been developed with the most commonly used scale called
the moment magnitude (Mw) scale. Moment magnitude is related to the physical size of
fault rupture and the movement or displacement across the fault, and as such is more
uniform measure of the strength of an earthquake. Another measure of earthquake size is
seismic moment. The seismic moment determines the energy that can be radiated by an
City of Inglewood General Plan Update Technical Background Report
6.2-1