Earthquake early warning systems: Current status and perspectives

William H. K. Lee¹ Juan M. Espinosa-Aranda^2
1U. S. Geological Survey, Menlo Park, CA, 94025, USA.
Tel. : +44--17 05-84 24 23, Fax: +44-17 05-84 25 21,
E-mail: whklee@ix.netcom.com
²Centro de Instrumentacion y Registro Sismico, Anaxagoras #814, CP 03020, Mexico, D.F., Mexico.
Tel. : +52-5-5 23 73 94, Fax: +52-5-6 69 25 12,
E-mail: maranda@servidor.unam.m

Abstract:
We will present a brief introduction of earthquake early warning systems, and discuss their current status and perspectives. As increasing urbanisation is taking place world-wide, earthquake hazards post strong threats to lives and properties for cities near major active faults on land or subduction zones offshore.

The physical basis for earthquake early warning systems is well understood, namely, destructive S-and surface waves travel at about half the speed of the P-waves, and seismic waves travel at much slower speed than signals transmitted by telephones or radios.

At least three earthquake early warning systems are now in operation: (1) Japan, (2) Mexico, and (3) Taiwan. These systems provide a few seconds to several tens of seconds of warning for large earthquakes. With recent emphasis on real-time seismology, operators of many regional and local seismic networks are now working hard to reduce the time of issuing an earthquake notice from several minutes to under a minute, thus gaining earthquake early warning capability.