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INTRODUCTION Based on nearly a century of experience, we know that global networks of seismic stations are essential to studies of such deep earth structures as the core-mantle boundary and mantle inhomogeneities and of many local and regional aspects of earthquakes, such as fault mechanisms. The results of such studies are the scientific under- pinning for an understanding of the causes of earthquakes, the genesis and emplacement of primary mineral deposits, and many other earth phenomena. At present we have, and we have had for some l5 years, an excellent global seismic network, the Worldwide Standardized Seismograph Network (WWSSN), which has done an admirable job of providing needed basic data. But there are many new problems, and the technology to tackle them with is now available. This is the time, therefore, to go ahead with the needed net- work improvements and to get on with the studies needed to attack critical problems. A major aim of this report is to encourage action in this direction. At present, we glean at most about 25 percent of the total information contained in WWSSN seismograms, because of instrumental deficiencies and the current method of data presentation. However, the improvements made in instrumentation in recent years have made possible more complete analysis of the entire signal from an earthquake. The following are but a few of the research areas that could be more effectively attacked if these improvements are made in our network capability: the mechanism of earth rupture (faulting); inhomogeneities of the earth; estimation of ground motion of engineering interest, in- cluding the siting of nuclear power plants; free oscil- lations of the earth; spatial and temporal distribution of release of stress in the earth; estimation of better earth models; better definition of earthquake source
(b) earthquake on August l9, l966. (Photo U.S. Geological Survey, R. E. Wallace.) (b) Sagging roof due to column failure at the Agricultural University from the earth- quake at Lima, Peru, on October 3, l974. (Photo L. A. Wyllie, Jr.)
parameters such as depth and size; and new definition of waveforms. A strenuous and comprehensive research effort in the areas given above is certainly in the national interest, since at least l4 federal agencies depend on seismological information in the discharge of their national responsi- bilities. Moreover, many major industriesâpetroleum, electric power (nuclear in particular), housing (and land use in general), mining, construction, and insurance, for exampleâwould benefit directly from improved funda- mental knowledge of earthquake sources and occurrences and of the general and detailed structure and dynamics of the earth. Seismologists of the United States have long cooperated with those of other countries through exchange of earth- quake data and research results. Such exchanges are necessary, since earthquakes occur in many parts of the earth and in many countries, large earthquakes are in- frequent, data from many observation points are needed to solve most problems, and there is a universal desire to mitigate the devastating effects of earthquakes wherever they strike (see Figure l). It is clear that global co- operation must continue.
