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l EXECUTIVE SUMMARY An earthquake produces seismic waves, which radiate from its focus, traveling around and through the earth, with size and persistence proportional to the dimensions of the source. Only a very few of the thousands of earth- quakes cataloged annually affect mankind directly. Most are perceptible only to seismographs—the scientific eyes and ears of the seismologist. From the seismograms, which display ground motion associated with the passing waves, comes our knowledge of the global distribution of earthquakes, of the internal structure of the earth, and of the earthquake source process. Interpreting the recorded seismogram requires sophisticated analysis procedures. Recent advances in analytical methods and instrumentation have increased dramatically the information to be gained from seismograms, but acquisition of adequate seismological data requires wide coverage by seismographs, globally, nationally, and regionally. Instruments must be maintained and upgraded regularly with the latest technology. Effective management is crucial for operations and data handling. All of these needs require adequate financial support over long periods of time. Seismographic networks provide data essential to programs such as the mitigation of earthquake hazards, the definition of geological structure on the margins and within tectonic plates, the safe siting of dams, power plants, and other critical facilities, and the investigation of dynamic processes of the earth. Operating a typical seismographic network is not overly expensive, but it does require dedication of time and talent by seismologists who run the stations. In many cases the major rewards are in providing data to help solve problems of national and global significance.

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The large number of questions on seismographic networks brought in recent months to the Committee on Seismology is strong evidence that there are critical problems with network operations. At the Workshop on Seismographic Networks, prompted by these questions, participants considered global, regional, and national networks collectively as an integrated system and also as entities with specific problems. This report discusses each component of the system in terms of rationale and problems, giving recommendations for solutions. A brief statement follows of major problems and major recommenda- tions for the global, regional, and national networks. Global Networks. Global networks are expected to provide for the scientific community a data base that continues indefinitely. Unfortunately, managing agencies find it difficult to recognize this long-term scientific importance. The service function of the networks, i.e., providing data for other users, must be considered in funding decisions by the managing agency. Global networks require continuing financial support at an adequate level. It is recommended (l) that consideration be given to transferring management responsibility for the global network from its present organizational base to another location within the U.S. Geological Survey or even to another agency, if such a change seems clearly advantageous; (2) that stable funding for global networks be sought from normal budgetary requests from within the U.S. Geological Survey, from the Defense Advanced Research Projects Agency, and from other agencies that use data from the networks; (3) that access to digital data and use of those data be improved while networks continue to meet fully the demand for and the global coverage provided by analog (i.e., visible) data at the present time; and (4) that procedures be established and funding be provided for the orderly and continuing interagency transfer of the most recent instrumentation and technology. Regional Networks. Regional network operations are beset with problems falling into three categories: functional definition, funding difficulties, and operational problems. Functional definition is the planned lifetime of a network, and a realistic estimate of it needs to be provided. Funding difficulties are of two types: a lack of stability on a year-to-year basis, and the vulner- ability of research funding being decreased to maintain

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network operations in times of fiscal stress when research funding is mixed with basic operational costs of the network. Operational problems are seen in a lack of coordination among networks, the need for a more standardized data base management system, and a growing obsolescence of network equipment. These problems are interrelated and difficult to order in importance. Recommendations are (l) that networks of planned, limited lifetime be reviewed every three to five years with respect to objectives and performance; (2) that the provision of data fundamental to research on seismotec- tonic processes and earthquake occurrence in the region be acknowledged by funding agencies as the main purpose of regional networks; (3) that an adequate data set from all regional networks be archived; (4) that data formats be standardized; and (5) that operations of networks be coordinated. National Network. The concept of a national network lacks general acceptance and widespread support by the U.S. seismological community, within which there is at present little coordination of network operations. The concept is sound, and support will grow with formulation of a suitable plan for implementation. Working Group on Seismic Networks. It is recommended that a Working Group on Seismic Networks be set up under the Committee on Seismology to provide continuity and uniformity in consideration of the various policy matters arising in network seismology. This group will provide the review functions recommended throughout this report for global, regional, and national networks. It should evaluate continually the health and status of regional networks, and advise on the development of a national network. The contributions to the earth sciences from seismic networks of all types have been substantial in the past two decades. We have entered the l980s with major advances in data acquisition, management, and processing techniques now available to seismology. The challenge is to build effectively on the present structure of networks, creating a new capability for addressing the next level of difficulty in the exciting problems of geoscience.