Seismic Monitors and Alarm Systems for Two Railways and A Water Utility
by Carl L. Strand
Presented at Pan Pacific Conference on Earthquakes, Volcanoes, and Tsunamis, Vancouver, British Columbia, Canada, July 29 - August 2, 1996

Seismic monitoring and alarm systems are being installed by two railway companies and a water utility to document vibrations or relay multiple levels of warning to operations centers. Eleven Los Angeles subway locations will be instrumented with digital accelerographs with dual seismic alarms. Following a low-level alarm, dispatchers will direct subway operators to slow down and stop at the next station; following a high-level alarm, they will direct subway operators to slow to a crawl and stop at the next station, and will also activate large tunnel exhaust fans. A commuter railway being built in Puerto Rico will install six dual seismic alarms; 5 at ground level and 1 in a subway. The low-level alarm will alert the operations center that an earthquake has occurred; the high-level alarm will automatically stop the trains. A water utility in the San Francisco Bay area is installing an error-tolerant system consisting of an accelerograph, 3 triaxial sensors, dual seismic alarms, and a 2-of-3 logic switch at each of 2 valves on distribution lines near fault crossings. The utility is also monitoring the roof, a freefield site, and a valve pit at 2 above-ground concrete water reservoirs with an accelerograph, 3 triaxial sensors, and dual seismic alarms at each site. For each of these 4 sites, the utility's SCADA alarm system will relay the seismic alarm(s) to the operations center, whose manager will consider them along with pressure and flow data, plus news from TV or radio, before directing any site's motorized valve to close.

Civic Center: An accelerograph/single-alarm seismic switch & a single-alarm seismic switch
Union Sta. : Two single-alarm seismic switches
Westlake Sta. : each
11 locations: 2 accelerograph/dual-alarm seismic switches (inst. bet. 1995 & 2000)
Setpoints: 0.10g (warning) & 0.20g (alarm)
Human intervention is required to direct trains to slow or stop
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6 stations: An adjustable dual-level seismic switch
Setpoints: 0.06g (Warning; human intervention)
0.12g (Stop-the-train; automatic)
Completion: 2001 AD
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2 valves at reservoirs: An accelerograph/dual-alarm seismic switch with one internal and two external triaxial accelerometers
2 valves at Hayward: An accelerograph/dual-alarm, 2-of-3- accelerometers
Fault: Triaxial
Setpoints: High-level alarm to be preset at 0.15g
Use of Data: Seismic alarms, plus pressure & flow data, plus info. from TV/radio, will all be considered prior to closing valves.

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