EARTHQUAKE WARNINGS GET A JOLT

Italian researchers have discovered a way to issue imminent warnings close to the impact of powerful earthquakes. Writing in today's issue of Geophysical Research Letters, scientists from the University of Naples and the Italian National Institute for Geophysics and Vulcanology claim to have found that the very early seismic signals from the vicinity of an earthquake can be used to quickly estimate its size. This could one day enable authorities to issue rapid alerts to affected populations to take immediate precautions in the case of large-scale events.

In their article, "Earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records", Aldo Zollo, Maria Lancieri, and Stefan Nielsen state that, after analyzing data from hundreds of earthquakes, telltale seismic waves 'recorded in the vicinity of an occurring earthquake source correlate with the earthquake magnitude and may be used for real-time estimation of the event size in seismic early warning applications.' They continue:

The earthquake size can be therefore estimated using only a couple of seconds of signal from the P- or S-wave onsets, i.e., while the rupture itself is still propagating and rupture dimension is far from complete. We argue that dynamic stress release and/or slip duration on the fault in the very early stage of seismic fracture, scales both with the observed peak amplitude and with the elastic energy available for fracture propagation. The probability that a fracture grows to a larger size should scale with the energy initially available.

P waves and S waves are the descriptors that geologists use for measuring pressure and shear forces from underground events, respectively. P waves typically travel slightly less than twice as fast as S waves, at about 5000 meters per second through rock, propagating much more quickly than the shear force that follows them. The Italian scientists said that they found that it takes only 2 seconds worth of analysis of the wave differentials from the onset of an earthquake to arrive at an estimate of its destructive potential using their new technique.

The Italian team noted that populations within 50 kilometers of the epicenter of a seismic event could potentially be alerted 10 seconds prior to the arrival of the main impact of an earthquake. Locations further away could receive additional warning time. To take advantage of this immediate alarm, the authors noted, new systems would have to be put in place to respond instantly to seismic activity alerts. They said systems could be installed at relatively low cost in developing nations, where moderate earthquakes can cause damage comparable to that wrought by larger ones in developed countries.

Mere seconds of warning may not sound like a lot of time, but it could mean the difference between life and death for many in an emergency. Moreover, as geophysical science advances, early warning systems will undoubtedly improve, particularly in regions known to be prone to seismic activity. In the future, capabilities such as this article reports joined with others currently under investigation may enable us to minimize the chaos of earthquakes.

[Editor's Note: For more on the science behind earthquake prediction, please see our cover story from last December, " Earthquake Alarm". For a free summary of the article by Zollo, Lancieri, and Nielsen, please see this account from the American Geophysical Union.]

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