- Earthquake Early Warning redirects here. For the earthquake warning system in Japan, see Earthquake Early Warning (Japan).
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 decisive event warnings.
Time lag and wave projection
An earthquake is caused by the release of stored elastic strain energy during rapid sliding along a fault. The sliding will start at some location and progress away from this hypocenter in each direction along the fault surface. 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 destructive 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 acomputer 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 signaled 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 people 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, Mexico and limited regions of Romania (the Basarab bridge in Bucharest) and the United States[1] are protected by earthquake early-warning systems.[2] The earliest automated earthquake pre-detection systems, named QuakeGuard, were installed in the 1990's by the company now known as Seismic Warning Systems of Scotts Valley, California. QuakeGuard technologycurrently protects over 40 locations, mostly across California, and has successfully detected multiple earthquakes with no false positive triggers, which is crucial to the effectiveness of such early warning devices. California's Calistoga fire station QuakeGuard installation automatically triggers a city-wide siren to alert the entire area's residents the moment any forewarning p-wave signature of a potentially dangerous quake is detected. Japan's Earthquake Early Warning system was put to practical use in 2006. Its scheme to warn the general public was installed on October 1, 2007.[3][4] It was modeled partly on the Urgent Earthquake Detection and Alarm System (UrEDAS) of Japan Railways, which was designed to enable automatic braking of bullet trains.[5]
See also
- Earthquake engineering
- P-wave
- Hayward fault - a typical slip-strike fault within a highly urbanized region
- Earthquake preparedness
- Seismic retrofit
References
- ^ Seismic Warning Systems. QuakeGuard technology
- ^ David Talbot. A technology review published by Massachusetts Institute of Technology on 2008-05-14. Retrieved on 2008-06-29.
- ^ "What is an Earthquake Early Warning?". Japan Meteorological Agency. Retrieved on 2008-06-29.
- ^ "Overview of the Earthquake Early Warning System" (in Japanese). Japan Meteorological Agency. Retrieved 2008-06-29.
- ^ Kumagai, Jean (June 2007). "A Brief History of Earthquake Warnings". IEEE Spectrum. Retrieved 2009-05-09.
External links
- Seismic Warning Systems
- CREWS: Coachella Valley Regional Earthquake Warning System
- European-Mediterranean Sismological Center, real-time earthquake information website.
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