Bay Area Digital Seismic Network

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ISBN 13 :
Total Pages : 9 pages
Book Rating : 4.:/5 (684 download)

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Download or read book Real-time Earthquake Alert System for the Greater San Francisco Bay Area written by and published by . This book was released on 1996 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of the earthquake alert system (EAS) is to outrun the seismic energy released in a large earthquake using a geographically distributed network of strong motion sensors that telemeter data to a rapid CPU-processing station, which then issues an area-wide warning to a region before strong motion will occur. The warning times involved are short, from 0 to 30 seconds or so; consequently, most responses must be automated. The San Francisco Bay Area is particularly well suited for an EAS because (1) large earthquakes have relatively shallow hypocenters (10- to 20-kilometer depth), giving favorable ray-path geometries for larger warning times than deeper from earthquakes, and (2) the active faults are few in number and well characterized, which means far fewer geographically distributed strong motion sensors are (about 50 in this region). An EAS prototype is being implemented in the San Francisco Bay Area. The system consists of four distinct subsystems: (1) a distributed strong motion seismic network, (2) a central processing station, (3) a warning communications system and (4) user receiver and response systems. We have designed a simple, reliable, and inexpensive strong motion monitoring station that consists of a three-component Analog Devices ADXLO5 accelerometer sensing unit, a vertical component weak motion sensor for system testing, a 16-bit digitizer with multiplexing, and communication output ports for RS232 modem or radio telemetry. The unit is battery-powered and will be sited in fire stations. The prototype central computer analysis system consists of a PC dam-acquisition platform that pipes the incoming strong motion data via Ethernet to Unix-based workstations for dam processing. Simple real-time algorithms, particularly for magnitude estimation, are implemented to give estimates of the time since the earthquake's onset its hypocenter location, its magnitude, and the reliability of the estimate. These parameters are calculated and transmitted with frequent updates as an 80-character digital string sent from the central analysis computer to pagers throughout the Bay Area in less than 2 seconds. We anticipate that the commercial sector will supply numerous and varied warning receiver systems once an EAS is considered operational. We focus on two prototype demonstration systems: (1) a pager-driven closure switch for opening fire station doors and (2) a pager display sign showing an of warning packet information. We will discuss the specific design features alert message and a display of this prototype system.