Earthquake Early Warning System is a system of accelerometers, seismometers, communication, computers, and Alerts that is devised for rapidly notifying adjoining regions of a substantial earthquake once one begins.
Earthquake Early Warning System is not the same as earthquake prediction, which is currently not capable of producing decisive event warnings.
An earthquake is caused by the release of stored elastic strain energy during rapid sliding along a fault. The sliding starts at some location and progresses away from the hypocentre 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 travelling faster than the shear wave. The pressure waves are always smaller in amplitude than the damaging shear waves that are the most destructive to structures, particularly buildings that have a resonant period similar to those of the radiated waves. Typically, these buildings are 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 a model of the region that determines appropriate responses to specific events.