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5 NATIONAL NETWORKS REVIEW The rationale for and a proper design of a state-of- the-art national digital seismic network were the subject of a comprehensive report prepared by the Panel on National, Regional and Local Seismograph Networks of the Committee on Seismology entitled U.S. Earthquake Observatories: Recommendations for a New National Network (NRC, l980). The major conclusions and overall recommendations from that report are included as Appendix C. Many of the recommendations set out in this report parallel closely those in the l980 report. This chapter considers those l980 recommendations in the context of global and regional networks, and in light of the current funding picture. U.S. seismographic networks were considered on a national basis, and' it was recommended that a concept be adopted of an integrated U.S. Seismograph System (USSS) so that the effect of damaging earthquakes on long-term national economic and security matters could be properly assessed and ameliorated. This application represents only a part of the overall role of the USSS, which would be a basic research tool in a variety of seismological investigations such as the detection and location of seismic events, studies of earth structure and processes, and site evaluations for critical facilities. The USSS is perceived to be a national and integrated system consisting of l. a national digital seismograph network 2. regional networks 3. data archiving and dissemination functions 4. management function including (a) a working group 27

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28 guiding the development of the USSS and (b) a working group on instrumentation and data handling 5. the National Earthquake Information Service (NEIS) A national digital seismograph network would consist of broadband, high-dynamic-range, three-component seis- mographs at a few tens of sites in the United States. It would serve as a stable interface between global seis- mographic networks and regional networks. It would provide a high-quality long-term data resource required for scientific and engineering purposes, giving uniform national coverage for earthquakes of magnitude 3.5 and greater. The availability of high-quality, three-component broadband, high-dynamic- range digital data will allow application of sophisticated, but proven, analytical methods to extract new information on earthquake source parameters, and on path properties and geometries that heretofore were not available in the lower-quality data. At present, elements of a national digital network exist, but they are not integrated. A mix of stations could be specified as selected units from l. national digital WWSSN 2. elements of regional networks 3. RSTN 4. national SRO/ASRO 5. U.S. Telemetered Seismic Network of l980, which serves the NEIS early location responsibilities by drawing on selected short- and long-period data generated by regional networks 6. National Tsunami Warning Network Clearly, coordination and some standardization of selected elements from these networks could constitute a national digital network. ASSESSMENT OF PROBLEMS To date there has been no commitment to or funding for the USSS concept. In the past, the seismological community has been slow to recognize the value of a coordinated and integrated national approach to some scientific as well as practical problems. Operators of the more mature regional networks stress that some of their problems could be alleviated by coordination and integration on a national scale. It is likely that costs

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29 would be significantly cut with an integrated system. Because of the low priority given to USSS by most of the seismological community, and because the funds recommended for this purpose do not seem to be obtainable in the near future, the federal government has not yet seen fit to endorse the total concept in the form of a commitment by any agency. It is important for the community to perceive that major elements of a national digital network exist in fact, and that evolution of USSS can be controlled in a manner designed to satisfy national needs and priorities. Many of the present regional networks, however, are products of parochial applied research objectives. There is currently little coordination at a national scale. Instrumentation, data handling functions, data processing, data exchange, and data archiving are thus not standard- ized. This state of affairs is not conducive to the development of long-term national integration of stations into USSS. RECOMMENDATIONS The committee endorses the adoption of the concept of an integrated U.S. Seismograph System. It is recommended that the Working Group on Seismic Networks to be established by the Committee on Seismology be charged also with guiding the development of the new integrated USSS and a move toward a national digital seismograph network. The nature of the working group is discussed in the introduction to this report. This working group should be the same group that represents the seismological community on the overall problems of seismograph networks, augmented with specialists from time to time as needed for problems specific to a national network. Members and specialists would include network data users, instrument specialists, computer specialists, academic network operators, an operator of an USNRC- funded network, and a USGS network operator. All members should be qualified, experienced seismologists, and, calling upon specialists as needed, they will recommend standards and options in the national network context related to the following topics: • instrumentation • network optimization • data processing and products • data management and archiving • data dissemination and centers for regional data