earthquake: Earthquake Warning Systems

Modern earthquake warning systems have been developed by several nations, and may be deployed nationwide or regionally. They depend on the detection of P waves by seismometers, and the transmission of that detection to affected populations by various means. Because P waves travel faster and are much less destructive than the later-arriving seismic waves an earthquake also produces, their detection can provide early warning, of a few seconds to several tens of seconds, of the arrival of the destructive shaking associated with an earthquake. If an earthquake's epicenter is close to a given location, however, the several types of waves will arrive closer together and little or no early warning will be possible.

Warning can be provided through several means including sirens and public loudspeakers, radio and television broadcasts, text messaging, and smartphone apps including dedicated earthquake-alert apps. More sophisticated systems can give some indication of the duration and severity of the earthquake. Early warning, even though measured in seconds, may permit people to take protective measures to prevent or limit injury, allow authorities to halt trains and subways and stop traffic from entering bridges and tunnels, and alert emergency responders to take measures to prevent their vehicles from becoming inaccessible or damaged.

Sections in this article:

• Introduction
• Major Earthquakes
• Earthquake Warning Systems
• Damage Caused by Earthquakes
• Seismic Waves
• Causes of Earthquakes
• Bibliography

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