Earthquake warning system

An earthquake warning system is a system of accelerometers, communication, computers, and alarms that is devised for regional notification of a substantial earthquake while it is in progress. This is not the same as earthquake prediction, which is currently incapable of producing actionable event warnings.

Time lag and wave projection

An earthquake is caused by the disruptive sliding of tectonic plates across a geologic fault. The sliding will start at some location and progress away from this epicenter in each direction along the fault. The speed of the progression of this fault tear is slower than and distinct from the speed of the resultant "pressure" and "shear" waves, with the pressure wave traveling faster than the shear wave. The pressure wave will generate an abrubt shock while the shear waves can generate a periodic motion (at about one cycle per second) that is the most destructive in its effect upon structures, particularly buildings that have a similar resonant period, typically buildings around eight floors in height. These waves will be strongest at the ends of the slippage, and may project distruptive waves well beyond the fault failure. The intensity of such remote effects are highly dependent upon local soils conditions within the region and these effects are considered in constructing a computer model of the region that determines appropriate responses to specific events.

Configuration

Earthquake warning systems consist of arrays of seismic motion sensors arranged throughout a region. High speed communications systems and computers collect the sensor readings and the computers are programmed to detect the likely strength and progression of the seismic event. If a dangerous event is detected then alarms can be signalled through the region likely to be affected, allowing warnings before local ground motion of up to and beyond twenty seconds. While short, such warnings would be sufficient to allow many persons to move to safer areas or to take shelter under substantial furnishings.

Transit safety

Such systems are currently implemented to determine appropriate real-time response to an event in determining train operator response for urban rail systems such as BART (Bay Area Rapid Transit). The appropriate response will be highly dependent upon the warning time, the local right–of–way conditions, and the current speed of the train.

Deployment

Japan, Taiwan and Mexico have earthquake early-warning systems. [David Talbot. A [http://www.technologyreview.com/Infotech/20772/?a=f technology review] published by [http://web.mit.edu/ Massachusetts Institute of Technology] on 2008-05-14. Retrieved on 2008-06-29.] Japan has the most advanced systems in the world. One of them was put to practical use in 2006, and its scheme to warn the general public was installed on October 1, 2007.cite news
url=http://www.jma.go.jp/jma/en/Activities/eew1.html
title=What is the Earthquake Early Warning?|publisher= [http://www.jma.go.jp/jma/indexe.html Japan Meteorological Agency] Retrieved on 2008-06-29.] [cite news|url=http://www.seisvol.kishou.go.jp/eq/EEW/kaisetsu/eew_naiyou.html|title=気象庁｜緊急地震速報について｜緊急地震速報の内容|date=|accessdate=2008-06-29|publisher= [http://www.jma.go.jp/jma/indexe.html Japan Meteorological Agency] |language=Japanese] Since before that another system for slowing down superexpress trains has been active in Japan.

ee also

*Earthquake early warning
*Earthquake Early Warning (Japan) - Japanise warning systems
*Earthquake prediction
*Hayward fault - a typical slip-strike fault within a highly urbanized region
*Household seismic safety
*Seismic retrofit

References