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2 INTRODUCTION The Workshop on Seismographic Networks was convened to consider the problems confronting network seismology and to provide scientific, technical, and management guidance to federal agencies, primarily regarding the operation of global, national, and regional seismographic networks. It was prompted by a number of related questions brought in recent months to the Committee on Seismology. This report is the result of that workshop. The National Research Council report, U.S. Earthquake Observatories (NRC l980), recommended establishing an integrated U.S. Seismograph System (USSS), the core of which would be a new national network of modern digital seismological observatories. The report called also for a guiding working group on the USSS to be established. Many of the problems discussed and several recommendations in this report are similar to those in the l980 study. Current constraints in federal funding, the potentially disastrous budget cuts nearly imposed in earthquake studies by several agencies in the fall of l98l, and the promise of continued stringencies all impart a sense of urgency to the need for clear position statements by the seismological community on U.S. seismographic networks. The global, national, and regional systems of seismographic stations, spanning the earth much like meteorological observatories, provide the fundamental data base for scientists to investigate the earth at different scales, addressing problems of earthquake hazards and prediction, safer sitings for critical facilities, and the identification of underground nuclear explosions, in addition to fundamental questions on the physical and chemical composition and geological structure and dynamics of the entire earth. Major advances in the earth sciences have come directly from

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these data. Agencies with responsibilities for maintain- ing subsets of this worldwide seismographic system have asked the Committee on Seismology for guidance in allocating their fixed or decreasing financial resources among competing scientific efforts. As the primary source of seismological data, networks have been and continue to be essential to the scientific health of seismology. The committee perceives a range of serious problems threatening this data base. The global network is insufficiently funded. All networks suffer from rising operational costs. Questions must be addressed on appropriate operational lifetimes. Much instrumentation is obsolete. Modernization of data acquisition and archiving methods is needed, and existing new approaches to data base management should be introduced to provide a creative environment for research. It is generally acknowledged that digital systems must ultimately replace analog, but at what cost? All of these efforts call for increased financial support at a time when the funding climate is inhospitable. The seismological data base demands stable continuity of support for operating networks that is independent of variations in research support. An important aspect of this report is the considera- tion, perhaps for the first time in such depth, of the interplay among the network systems of differing scales and purposes—global, national, and regional—and their definition as a major scientific resource for acquisition of important data. In this unification the national network becomes the linkage by which regional networks are integrated with the global seismographic systems. Thus, that portion of the global network located within the United States can be viewed as a subset of the national network, which in turn is a subset of stations from regional networks. The rationale for such a structure is to facilitate exchange of data, methods of analysis, and scientific results, by enlisting the involvement of present network operators in the system. In order to review in depth the present state of difficulties facing the networks, the committee solicited assessments and opinions from a range of network operators, users, and supporting agencies. A compre- hensive questionnaire was formulated and distributed to operators of regional networks. Forty-five completed questionnaires were returned by federal and state agencies and universities, providing an unprecedented and substantial overview of regional seismographic networks

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operated for a variety of purposes by U.S. scientists. Appendix B gives the questionnaire, a list of the respondents, and a summary of the resulting information. Even before the workshop began, the need for a continuing working group that would address practical problems of seismic networks from a perspective different from that of any one agency was recognized. The Committee on Seismology plans to establish a working group on seismic networks within the National Research Council, for if it does not, the committee's agenda for years to come will be dominated by network questions. The working group will be asked for policy recommenda- tions on the interrelationships among global, national, and regional networks. Other, more specific, questions for the working group are given throughout this report. The working group, which will report to the Committee on Seismology, is to consist of at least five individuals with overlapping terms of about five years. Network problems are not quickly solved. It is therefore important for a majority of members of the working group to serve long enough to show some results from changes in network policy. We anticipate that the working group will often need to seek the advice of specialists, particularly in recommending technological improvements. The report considers global networks in Chapter 3 and regional networks in Chapter 4, reviewing the nature and use of each, identifying the problems peculiar to each, and recommending various approaches toward solutions to the problems. Chapter 5 reviews the concept of a new national network and its place in the present network structure. By virtue of the variety of issues, the recommendations range from specific actions to acknowledgments of remaining outstanding difficulties requiring further attention. Background information for the workshop is presented in Appendixes A through C.