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 Reducing Earthquake Losses Throughout the United States

In coping with recent multibillion-dollar earthquake disasters, scientists and emergency managers have found new ways

to speed and improve relief efforts. This progress is founded on the rapid availability of earthquake information from

seismograph networks.

For many years now, seismograph networks in earthquake-prone areas of the country have been providing scientists with valuable

information for earthquake research. Actions taken following two recent large earthquakes show how the same information from

seismograph networks can be used in very practical and immediate ways during disaster-relief efforts.

Ten seconds of strong ground shaking on the northern edge of the Los Angeles metropolitan area left more than 40,000 people

homeless and as many as 16,000 residences unsafe for occupancy after the 1994 Northridge earthquake in southern California.

While police and fire departments, medical emergency teams, and citizens rescued people and fought fires, emergency managers

were faced with deciding what resources would be needed to shelter people and to help people recover from the disaster. These

decisions would affect thousands of people whose lives were shattered or disrupted by the violent earthquake.

In responding to the disaster, emergency managers were aided by scientists and engineers from the U.S. Geological Survey

(USGS) and other institutions and agencies. Scientists and engineers quickly prepared a shaking-intensity map for all parts of the

greater Los Angeles area; this map showed estimated severity of shaking and the level of damage likely associated with such

shaking. This map was available long before a complete picture of the damage could be assembled. It enabled emergency

managers to promptly locate the hardest hit areas and to send appropriate help. Victims whose homes were destroyed or severely

damaged were directed to shelter before a predicted storm added to their misery. Teams of relief workers were sent where they

were most needed in the days following the quake. The map also helped emergency managers reduce the time for delivery of

relief money to individuals from weeks to hours.

The shaking-intensity map prepared after the Northridge earthquake was the first use of such a map to help focus relief efforts

during a disaster. Seismologists have known for many years that damage from an earthquake is not evenly distributed about its

epicenter. Although damage typically does decrease with distance from the earthquake source, local geologic conditions can

greatly alter this pattern by amplifying shaking in specific areas; this fact is what makes shaking-intensity maps prepared after an

earthquake such a valuable tool for emergency managers.

(Click on image for a full size version - 198K)

A rapidly prepared map of probable shaking intensity throughout the greater Los Angeles Area that was

used to bring timely emergency services to tens of thousands of victims after the devastating Northridge

earthquake on January 17, 1994. Six levels of shaking intensity are shown by different colors. Red near

fault (bold white line) shows area that shook most violently.

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Cypress

(Click on images for full size versions - 139K, 131K, 125K)

Photographs show typical damage associated with different levels of shaking: light damage

(top-left), moderate damage (top-right), and heavy damage (bottom-left).

To prepare accurate shaking-intensity maps quickly after an earthquake, essential information about the location, size, and nature

of the earthquake must be brought together. A comprehensive broadcast system for reporting this essential information was

established in 1991 in southern California. The broadcast system, called CUBE (Caltech-USGS Broadcast of Earthquakes,

automatically reports earthquakes recorded by the 350-station southern California seismograph network operated by the USGS

and the California Institute of Technology (Caltech). A companion seismograph network and broadcast system reports

earthquakes in northern California; similar networks are located in other earthquake-prone areas of the nation.

Whenever a sizable earthquake strikes, designated scientists are notified via pager. Subscribers to this systemÑsuch as railroad

companies, utility companies, and television stationsÑare also simultaneously notified. Instead of a telephone number, the

location, size, depth, and other information about the earthquake scroll across the pager display. This information can be fed into a

computer modeling system, which incorporates geologic conditions of an area. When a sizable earthquake occurs, scientists can

use the modeling system to calculate the shaking intensity for different locales within a large area surrounding the earthquake's

epicenter. They are then able to combine this information to produce a shaking-intensity map that can be used by emergency

managers.

The shaking-intensity map prepared after the Northridge earthquake provided an easy-to-understand picture of how shaking

varied throughout the greater Los Angeles area and thus how different areas were affected. During future earthquakes expected in

both southern and northern California, shaking-intensity maps can be used to focus relief resources in the hardest hit areas. When

such maps are prepared within hours of a large earthquake, they have enormous potential to help disaster-relief workers quickly

deliver medical help, food, and water to survivors. These maps can also be useful in directing the newly homeless to shelter.

While shaking-intensity maps are one valuable benefit of the rapid availability of information from seismograph networks, there

are other practical ways this information can be used. For example, information from the northern California seismograph

network was used to warn workers of numerous aftershocks as they razed the collapsed Cypress freeway viaduct in Oakland,

California, following the Loma Prieta earthquake in 1989. USGS scientists set up a system that warned workers via radio about

25 seconds before the precarious structure would begin to shake from an aftershock. These warnings, made possible because radio

waves travel much faster than seismic waves, were sent from detecting instruments in the aftershock area--some 50 miles

away--to a receiver at the Oakland worksite. Each time the instruments detected an aftershock, the receiver sounded an alarm that

enabled workers to move to safety during the danger period.

(Click on images for full

size versions - 84K, 145K,

29K)

Basic elements of the

broadcast system that transmits information about earthquakes in

southern and northern California. Energy from earthquakes is recorded at numerous field

stations on instruments called seismographs. These seismic signals are relayed nearly

instantaneously from this seismograph network to analysis centers at the California Institute of

Technology (Caltech) in Pasadena and at the U.S. Geological Survey in Menlo Park. From these centers, earthquake information

including time, location, and magnitude is relayed to designated scientists and to system subscribers via pager (top right) within

1 or 2 minutes of an earthquake. The information can also be displayed as a map on a personal computer (top left).

(Click on image for a full size version - 221K)

Twisted remnant of the Cypress freeway viaduct in Oakland, California, following its partial collapse during the Loma Prieta

earthquake in 1989. Because aftershocks of a large earthquake can cause additional shaking and damage, information from a

seismograph network near the earthquake's epicenter was used to warn workers dismantling this structure about 25 seconds

before the structure would begin shaking again. (Click on image for full-size version, 224 Kbytes.)

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Both these examples show how rapid, reliable information from seismograph networks, until recently used primarily for research,

is now proving its value during earthquake disaster-relief operations. This information provides emergency managers with a

means for coping more effectively with the earthquake disasters that are expected in the future.

Carl Mortensen, Carolyn Donlin, Robert A. Page, and Peter Ward

COOPERATING AGENCIES, COMPANIES, AND INSTITUTIONS

California Governor's Office of Emergency Services

California Institute of Technology

EQE International

Federal Emergency Management Agency

University of California, Berkeley

For more information contact:

Earthquake Information Hotline (415) 329-4085

U.S. Geological Survey, MS 977

345 Middlefield Road, Menlo Park, CA 94025

U.S. Geological Survey Fact Sheet-097-95, March 1995

USGS Menlo Park Earthquakes Home Page

Return to Factsheet index

Web page by Will Prescott - 1996 April 9

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