Menu
Contact Us Search
Organization Title

NR 2004-01
January 12, 2004

Contact: Ed Wilson
Mark Oldfield
Don Drysdale
(916) 323-1886

STATE HAS MADE STRIDES IN EARTHQUAKE SAFETY
SINCE DEVASTATING 1994 NORTHRIDGE QUAKE

Click Here for more information related 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.

###