DEFINITION OF EARTHQUAKE WARNING SYSTEMS

Saving lives during earthquakes is critically dependent on three

major issues: knowing the hazards, planning accordingly, and

receiving adequate warning that an earthquake is occurring. During

earthquakes seismic waves travel outward from the epicenter,

traveling at up to several miles per second. For large earthquakes,

significant damage may be inflicted on structures tens or even hundreds

of miles from the epicenter, several or several tens of seconds

after the earthquake first strikes in the epicentral region.

Typically the most destructive surface waves travel more slowly

than P and S waves, and at distances of more than a few miles, the

time difference can be significant. Earthquake engineers and urban

planners are utilizing these basic physical realities to devise and

implement some extremely sophisticated earthquake warning systems

for places like southern California and Japan. Seismographs

are being linked to sophisticated computer systems that quickly

analyze the magnitude of an earthquake and determine if it is going

to be destructive enough to merit a warning to a large region. If a

warning is issued that a large earthquake is occurring, the systems

use satellite and computer networks to send a warning to the surrounding

areas to immediately take a prescribed set of actions to

reduce the damage, injury, and death from the earthquake. For

instance, trains may be automatically stopped before they derail,

sirens may sound so that people can take shelter, nuclear plants

can be shut down, and gas lines can be blocked. These warning

systems may be able to alert residents or occupants of part of the

region that a severe earthquake has just occurred in another part

of the region, and that they have several or several tens of seconds

to take cover. The thought is that if structures are adequately constructed,

and if people have an earthquake readiness plan already

implemented, they will know how and where to take immediate

cover when the warning whistles are sounded, and that this type of

system may be able to save numerous lives.

The effectiveness of earthquake warning systems depends on

how adequately the plans for such an event were made. Ground

shaking causes much of the damage during earthquakes, and the

amount of shaking is dependent on the type of soil, bedrock, the

geometry or focal mechanism of the earthquake, and how local geologic

factors focus the energy to specific sites. Geologists are able

to map the different soil and shaking hazard potentials and build a

computer-based database that is useful for emergency response.

For instance, a type of map known as a shake map may be rapidly

generated for specific earthquakes, showing how much shaking

might have been experienced in different areas across a region. If

the types of buildings and their susceptibility to shaking are known,

the consequences of earthquakes in specific neighborhoods can be

predicted. Emergency responders can then immediately go to the

areas that likely received the most damage, saving lives and helping

the most injured before responding to less severely hit areas.

Place Year Deaths Estimated Magnitude

Shanxi, China 1556 830,000

Calcutta, India 1737 300,000

T’ang Shan, China 1976 242,000 m. 7.8

Gansu, China 1920 180,000 m. 8.6

Messina, Italy 1908 160,000

Tokyo, Japan 1923 143,000

Beijing, China 1731 100,000

Chihli, China 1290 100,000

Naples, Italy 1693 93,000

Gansu, China 1932 70,000

1556 in China that killed 800,000–900,000 people. One in

Calcutta, India, in 1737 killed about 300,000 people.

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