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to the Northridge earthquake.
LOS ANGELES – The
Northridge earthquake of January 17,
1994 killed 61 people and was one of the
worst natural disasters in U.S. history,
on a par with Hurricane Andrew in terms
of financial loss. The magnitude 6.7
temblor caused some of the strongest
ground motion ever recorded and left
thousands temporarily homeless.
Scientists try to
learn from every earthquake. Northridge
– caused by a previously unknown fault
nine miles underground -- demonstrated
that blind-thrust faults might be more
common and destructive than previously
believed. It produced surprisingly
strong near-source ground motion,
resulting in upgrades to the Uniform
Building Code. It showed that modern
steel-frame buildings were not as
earthquake-resistant as engineers
expected, prompting engineers to develop
new types of beam-column connections. It
also taught a lesson about how complex
geology can be; communities such as
Santa Monica were more heavily damaged
than others closer to the epicenter.
“Perhaps most
important, the Northridge earthquake
drove home the point that there’s no
such thing as too much preparation,”
California Department of Conservation
Director Darryl Young said. “While the
Los Angeles area was and is perhaps the
best-prepared locale in the world for a
large earthquake thanks to retrofitting
and well-enforced building codes, the
Northridge quake caused more than $40
billion in damage.”
The California
Geological Survey – part of the
Department of Conservation -- is one of
the many government entities that have
worked to improve public safety through
seismic instrumentation, seismic hazard
mapping and zoning, and other projects
in the last decade.
“The Northridge
earthquake was not an unusual event,”
said Mike Reichle, acting State
Geologist and head of the California
Geological Survey. “There have been
several earthquakes similar in size to
or larger than Northridge in California
since 1971. Earthquakes large enough to
cause damage and fatalities are
inevitable, the most recent example
being the magnitude 6.5 event near Paso
Robles that killed two people. It’s
critical that we continue to improve our
understanding of earthquakes and to
increase our readiness.”
The California
Geological Survey’s Strong Motion
Instrumentation Program (SMIP) installs
monitoring devices called accelerographs
throughout California to measure the
vertical and horizontal response of
structures and soils to strong
earthquake shaking. The analysis of this
data is used to recommend changes to
seismic designs and practices for
buildings, bridges and other structures
and to aid emergency response personnel
in the event of a disaster. SMIP
maintains more than 1,000 accelerographs
statewide.
As a result of the
Northridge earthquake, SMIP partnered
with the California Institute of
Technology, and the U.S. Geological
Survey’s Pasadena office in TriNet, a
seismic network that conducts earthquake
research, monitoring and early warning.
Completed in 2001, the Southern
California portion of the network
includes nearly 600 monitoring stations.
An important new
product was also an outgrowth of
Northridge. Accurate information is an
important commodity in the wake of an
earthquake because it saves lives, time,
effort and money. TriNet produces a
ShakeMap of ground shaking, based on
motion recorded by stations in the
network, within minutes following an
earthquake. The ShakeMap identifies
areas of the greatest potential damage
for use by the Office of Emergency
Services and other emergency response
personnel. These maps will help
authorities concentrate their recovery
efforts more effectively in a damaging
earthquake.
TriNet recently has
evolved into a statewide system, which
also includes UC Berkeley and USGS at
Menlo Park. In July 2001, the California
Office of Emergency Services obtained
funding for the California Integrated
Seismic Network (CISN), a statewide
system that includes the TriNet
stations. The CISN will improve seismic
instrumentation and provide statewide
ground shaking intensity maps. It will
also distribute and archive
strong-motion records of engineering
interest and seismological data for all
recorded earthquakes, and provide
training for users.
Since the Northridge
earthquake, the California Geological
Survey has installed or upgraded more
than 500 seismic monitoring stations.
Some of the significant structures
involved including two that collapsed
during the Northridge earthquake: The
Interstate 5/Highway 14 interchange
north of San Fernando and the Interstate
10 bridge at La Cienega Boulevard in Los
Angeles.
"The scientific
resources of our partners work
hand-in-hand with our engineering
expertise to ensure that the
transportation system is ready for any
emergency," said Doug Failing, Caltrans
District Director for Los Angeles and
Ventura counties.
While the 1989 Loma
Prieta earthquake prompted the creation
of the state’s Seismic Hazard Mapping
Program, the Northridge earthquake
“really jump-started the program,”
according to the program’s Supervising
Geologist, Chuck Real.
Following Northridge,
the Federal Emergency Management Agency
offered the California Geological Survey
funding to map Ventura, Los Angeles and
Orange counties for the secondary
earthquake hazards of landslides and
liquefaction. Thus far, 106 maps have
been released for northern and southern
parts of the state. They cover 6,000
square miles of land that has a
population of 13 million and an average
annual construction volume of $11
billion.
Ventura and Orange
counties are completely mapped; the
final seven maps for Los Angeles County
are in the preliminary stage. Mapping of
San Francisco Bay Area counties only
began in the last couple of years.
The Seismic Hazards
Mapping Program has identified about 345
communities as high-risk areas for
earthquakes. Fewer than half have been
zoned. Riverside and San Bernardino
counties are among those on the
program’s priority list.
“We still have a lot
of work to do,” Real said. “Several
local governments – especially San Diego
and some areas of Northern California –
have asked to be zoned.”
While violent shaking
causes most of the damage in large
earthquakes, liquefaction and landslides
can take their toll, too. During the
Northridge earthquake, liquefaction was
a major cause of damage in the Kings
Harbor area of Redondo Beach. The quake
also caused more than 11,000 landslides,
some of which damaged structures or
blocked roads.
Cities and counties
use the maps to regulate development. If
property is located in a Zone of
Required Investigation, where
liquefaction or earthquake-induced
landslides could occur during a large
earthquake, local government must
withhold development permits until the
level of hazard has been determined by a
detailed geotechnical investigation at
the construction site. If hazards are
present, mitigation measures are
incorporated into development plans.
Property sellers and
real estate agents must inform buyers if
property they're selling is in a Seismic
Hazard Zone, as is the case when
property is in a designated flood zone.
“There has been
aggressive support of the act in most
places,” Real said. “We’re not just
identifying hazards; we’re having a real
impact on the procedures that local
governments and businesses use to make
structures safer.”
In addition to
studying and mapping earthquakes and
other geologic phenomena, the Department
of Conservation maps and classifies
areas containing mineral deposits;
ensures reclamation of land used for
mining; regulates oil, gas and
geothermal wells; administers
agricultural and open-space land
conservation programs; and promotes
beverage container recycling.
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