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APPENDIX C SUMMARY AND MAJOR RECOMMENDATIONS OF U.S. EARTHQUAKE OBSERVATORIES: RECOMMENDATIONS FOR A NEW NATIONAL NETWORK The report on U.S. Earthquake Observatories is the first attempt by the seismological community to rationalize and optimize the distribution of earthquake observatories across the United States. The main aim is to increase significantly our knowledge of earthquakes and the earth's dynamics by providing access to scientifically more valuable data. Other objectives are to provide a more efficient and cost-effective system of recording and distributing earthquake data and to make as uniform as possible the recording of earthquakes in all states. Many problems of major national importance related to earthquakes remain to be solved. Earthquake prediction and the amelioration of earthquake hazards, for example, require uniform, continuous, and standardized earthquake records over the entire country using modern computer- coupled instrumentation. We cannot anticipate all the scientific gains that will accrue from sharply improving the national capability to observe, measure, and study earthquakes, but we can be reasonably sure of many successes. Among the research goals are the quantitative study of sources of earthquakes above magnitude 3.0 up to the greatest earthquakes in the entire United States, a capability never before possible; more reliable under- standing and prediction of strong ground shaking; the precise definition of fine structure in the earth's crust and deep interior using high-resolution techniques; and the close mapping of regional tectonics, related to geological hazards, and location of natural resources. In particular, there is a need to monitor and analyze quickly short-term stress variations in active fault zones for earthquake prediction purposes, a high national priority. 59
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60 EH ID M e a 5 ta z
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6l Two recent developments make the present an appropriate time to move ahead by redesigning and consolidating the uncoordinated mixture of local, regional, and national earthquake observatories, many of which are obsolescent. The first development is the new technology based on digital sampling of signals. The second is the decisive advance in theoretical seismology, including powerful computational ability, that has created a need for high-quality observations of seismic waves, with wide dynamic ranges in both frequency and amplitude. For the attainment of research and applied goals, data analysis, archiving, and retrieval capabilities in the United States need streamlining, partly centralizing, so that digital tapes, seismograms, and the derived seis- micity data from all stations are available in a short time to all users. In order to bring together these components, the central recommendation of the Panel is that the guiding concept be established of a rationalized and integrated seismograph system consisting of regional seismograph networks run for crucial regional research and monitoring purposes in tandem with a carefully designed, but sparser, nationwide network of technologically advanced observatories. Such a national system must be thought of not only in terms of instrumentation but equally in terms of data storage, computer processing, and record availability. Exhibit C-l shows the suggested locations of seismograph stations for the proposed National Digital Seismograph Network (NDSN). In order to take advantage of recent technological and theoretical advances, the concept of an integrated United States Seismograph System (USSS) should be adopted in the United States so that enhanced information on earthquake sources, seismic hazards, ground motions, and earth structure is available.