Automated Seismic Event Monitoring System (NUREG/CR-6625, Addendum 1)
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Manuscript Completed: August 2001
Date Published: September 2001
I. Henson, R. Wagner, W. Rivers, Jr.
1441 McCormick Drive
Largo, MD 20174
E. Zurflueh, S. Pullani , NRC Project Managers
Division of Engineering Technology
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
NRC Job Code Y6063
The U.S. Nuclear Regulatory Commission (NRC), as part of its actions for insuring public safety, wishes to be able to monitor seismic activity in near-real time. To help achieve this capability, a data recording, processing, and archiving system was constructed to detect seismic signal arrivals, calculate epicenters and seismic magnitudes, and issue alerts whenever a strong earthquake is determined to have occurred near the site of a nuclear power plant. This system takes as its input raw waveforms that have triggered signal detectors at stations of the U.S. National Seismographic Network (SNSN) and that have been re-broadcast via satellite from the U.S. Geological Survey (USGS) to a Very Small Aperture Terminal receiver at NRC, so the system is able to perform its calculations within minutes of the earthquake. The epicenters that are calculated by the system are crude, however, so as soon as improved event locations are calculated by USGS they are downloaded via the Internet and used in place of the epicenters that had been calculated at NRC in near-real time. Seismograms that were not received at NRC via the satellite link are also retrieved via the Internet, sometimes months after the event, and they are then added to the permanent seismogram archive.
In addition to determining earthquake epicenters and magnitudes automatically, the software system permits the seismograms to be studied off-line by means of stand-alone seismic data analysis packages that are operated by a scientist or data analyst using interactive graphics on a UNIX workstation. One of these stand-alone packages permits the seismograms recorded at the USNSN stations to be used to estimate the Cumulative Absolute Velocity (CAV) at nearby nuclear power plant sites. These calculations make use of tables of frequency-dependent site effects that were computed for power plant sites on the basis of local geologic structures. Another part of the off-line software is a Geographic Information System that permits the newly computed epicenters, the locations of the seismic stations, and the power plant sites all to be displayed on the workstation ini interactive maps that show a detailed context of the geologic and geophysical data sets which affect seismic wave propagation and other important physical phenomena.
The software for near-real time seismic analysis has recently been re-written in the Java programming language. As a part of this re-writing of the code, a graphical interface has been developed that permits information about recent and archived events to be displayed via tables and that permits the raw waveforms to be viewed and manipulated graphically in both the time and frequency domains. The seismograms can be displayed as soon as they are received from the satellite or after the events have been detected and located. Because both the analysis and system is platform-independent.
This addendum documents the results of additional work performed on the Automatic Seismic Event Monitoring System following the original publication of NUREG/CR-6625 in May 2000.