F.G. Fischer
E.G. Jensen
J. VanSchaack
W. H. Bakun
1994
<p><span>A prototype early warning system to provide San Francisco and Oakland, California a few tens-of-seconds warning of incoming strong ground shaking from already-occurred </span><i>M</i><span> ≧ 3.7 aftershocks of the magnitude 7.1 17 October 1989 Loma Prieta earthquake was operational on 28 October 1989. The prototype system consisted of four components: ground motion sensors in the epicentral area, a central receiver, a radio repeater, and radio receivers. One of the radio receivers was deployed at the California Department of Transportation (</span><span class="sc">CALTRANS</span><span>) headquarters at the damaged Cypress Street section of the I-880 freeway in Oakland, California on 28 October 1989 and provided about 20 sec of warning before shaking from the </span><i>M</i><span> 4.5 Loma Prieta aftershock that occurred on 2 November 1989 at 0550 UTC. In its first 6 months of operation, the system generated triggers for all 12 </span><i>M</i><span> > 3.7 aftershocks for which trigger documentation is preserved, did not trigger on any </span><i>M</i><span> ≦ 3.6 aftershocks, and produced one false trigger as a result of a now-corrected single point of failure design flaw. Because the prototype system demonstrated that potentially useful warnings of strong shaking from aftershocks are feasible, the </span><span class="sc">USGS</span><span> has completed a portable early warning system for aftershocks that can be deployed anywhere.</span></p>
application/pdf
10.1785/BSSA0840020359
en
Seismological Society of America
Early warning system for aftershocks
article