Earthquake Safety Systems, Inc.
The #1 source for earthquake actuated shutoff systems for
industrial and commercial loss mitigation.
If you are near the 'focus' or, 'epicenter' of the earthquake, there will be little or no early warning- independent of whether, or
not, you subscribe to a broadcast warning system or a site specific warning system. However, with increasing distance from the earthquake's
focus, there is a progressively longer opportunity for advance warning ranging from a few seconds to 20 seconds, or more.
warning is currently available by either subscribing to a signal broadcast by a government agency/university (i.e. USGS 'ShakeAlert'
EEW system) or, by in-situ detection of the arrival of the earthquake's 'p-wave'- which travels faster than the typically more damaging
s-waves. There are a number of variables which make it difficult to say which system provides the greatest advance warning. Certainly
an alarm signal broadcast via radio waves will travel fast and far- with the potential to notify a large exposed population. In fact,
current seismic networks can roughly project what the magnitude of the event will be after just the first few seconds of shaking!
However, depending upon the distance of the closest seismic station to the earthquake focus and alarm propagation times to the end-user,
it is conceivable that 5, 10- even 20 seconds might pass between the actual start of the event and the receipt of a broadcast
alarm signal (the blind zone). If you are within 30 km from the focus you might not get very much 'useable' advance warning from a
broadcast based system. Also, the broadcast warning signal must be converted into an alarm signal applicable to your operation- which
adds more propagation delay. Some argue that broadcast signals increase the potential for false positives or other, unnecessary shutdowns.
However, in the 'blind zone', a 'site-specific' seismic switch (i.e. Saturn S-001) would trip on the arrival of the p-wave
and provide critical seconds of warning (initiating an automated response)before the more damaging s-wave arrived- and BEFORE the
government broadcast alarm signal is received.
"We are now taking the person out of the loop; so for an earthquake
right under the BART system, we get an immediate initiation of braking without anybody having to think. It's a faster response
than we would have otherwise".
- Kevin Copley, BART Manager of Computer Systems Engineering, BART TV/ Mobile Site, September 27, 2012.
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