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Note: The map
can be viewed
here.
SACRAMENTO – The
Department of Conservation’s California
Geological Survey today released a new
regulatory Seismic Hazard Zone map that
shows the risk of liquefaction and
landslides in portions of Los Angeles
and Orange counties, as well as a county
not previously zoned, San Bernardino.
“Seismic Hazard Zone
maps are good examples of the state’s
commitment to earthquake preparedness,”
said Mike Chrisman, Secretary for
Resources. “They are important tools in
the effort to protect public safety.”
Liquefaction and
landslides are potential side effects of
earthquakes in the magnitude 5.5 or
greater range that can cause destruction
over and above the damage done by
shaking.
“This map identifies
the areas where liquefaction and
landslides are more likely to occur,”
said State Geologist John Parrish, head
of the California Geological Survey.
“With that knowledge, local planners and
the building community can take steps to
minimize the danger by ensuring that new
construction takes into account not only
that we’re in earthquake country, but
also that there are concerns other than
shaking.”
The Yorba Linda
Quadrangle map covers approximately 60
square miles in eastern Los Angeles,
northern Orange and western San
Bernardino counties. The Orange County
portion includes parts of the cities of
Anaheim, Brea, Fullerton, Placentia and
Yorba Linda. The community of Chino
Hills in San Bernardino County is
covered. Within Los Angeles County, most
of Diamond Bar and a small part of the
City of Industry are covered in the
northern part of the map.
Earthquake-induced
landslide zones encompass more than a
third of the map due to a combination of
hilly terrain and relatively low rock
strength. Liquefaction zones are
restricted to stream channels and their
adjacent floodplains, some canyon
bottoms, and a small area in the map’s
northwest corner.
Liquefaction – which
occurs when water-saturated, sandy soil
is shaken violently and temporarily
loses its ability to support structures
– was a major cause of damage in the
Kings Harbor area of Redondo Beach
during the Northridge earthquake of
1994. The Northridge earthquake also
caused more than 11,000 landslides, some
of which damaged structures or blocked
roads.
If the site-specific
geotechnical studies conducted prior to
development reveal that liquefaction or
landslide hazards are present,
mitigation measures are incorporated
into development plans.
The program has
identified about 345 California
communities as high-risk areas for
liquefaction and/or landslides; 160 have
been zoned. There are now 109 Seismic
Hazard Zone maps covering all or
portions of eight counties.
To establish its
priority list, the program looks at the
level of seismic hazard in each locale
as well as the amount of new development
going on. Work is ongoing in Riverside
County.
In addition to
studying and mapping earthquakes and
other geologic phenomena, the Department
of Conservation regulates oil, gas and
geothermal wells; ensures reclamation of
land used for mining; administers
agricultural and open-space land
conservation programs; and promotes
beverage container recycling.
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