Research shows early detection of earthquake magnitude possible

Published 7 December 2006

Italian researchers find string correlation between strength of primary wave and the damage resulting from the secondary wave; basic math now permits 10-15 seconds warning time for those near the epicenter; early warning could trigger emergency response mechanisms

Until recently, seismologists have had to wait until after an earthquake to pronounce its magnitude on the Richter Scale. By that point, however, the question is merely academic. For those interested in creating an early warning system, however, what is needed is a method that identifies an earthquake’s strength before the event is complete. Two teams of Italian scientists believe they have found such a system, one that could provide those living at the epicenter at least ten seconds warning time — enough, perhaps, to activate fire retardant systems. It is still not very much compared with the warning system being developed for tsunamis, but it is a start.

The researchers at the University of Naples the National Institute of Geophysics and Vulcanology in Rome found that earthquake magnitude can be estimated using just two seconds worth of signal from the first recorded P (primary) and S (secondary) waves. Stress release and slip duration on the fault in the very early stage of seismic fracture, the scientists discovered after studying data from 200 local earthquakes, is strongly related to the observed peak amplitude of the early P wave and to the elastic energy available for propagation of the fracture.

The rest is just simple math. Primary waves travel at four miles per second, covering approximately forty miles in ten seconds. Secondary waves, which are usually more destructive at only 2.2 miles per second, covering 11 miles in 10 seconds. Therefore, a city located around 40 miles from an epicenter would have around fifteen seconds of lead time to prepare for an earthquake’s impact, the time difference between the arrival of the first P wave at a recording station near the epicenter and the arrival of the S wave at the city itself.

The study was funded in part by the consortium Analisi e Monitoraggio del Rischi Ambientali (AMRA) through the European Union-Seismic Early Warning for Europe (EU-SAFER) project. The study will be published later this month in Geophysical Research Letters.

-read more in this American Geophysical Union release