Global Earthquake Monitoring, Its Uses, Potentials, and Support Requirements (1977) / Chapter Skim
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The Worldwide Standardized Seismograph Network
The Worldwide Standardized Seismograph Network
Pages 11-22
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From page 11... ...
Responsibility for the installation and management of the network, supported by Department of Defense funds, was assigned to the Coast and Geodetic Survey of the Department of Commerce, a federal agency with years of experience in the operation of conventional seismic observatories. In l972, responsibility for operation and maintenance of the WWSSN was transferred to the U.S.
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From page 12... ...
A simple switching mechanism can vary the FIGURE 3 Components of the WWSSN station. Encased longperiod seismometers are shown in the upper left and longperiod photographic recording equipment in the lower left; encased short-period seismometers are shown in the upper right and short-period photographic recording equipment in the lower right.
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From page 13... ...
Within the seismological community there is general agreement that the WWSSN has been an outstanding success as a research tool (see Appendix B) as well as an effective stimulant to seismic studies at a number of institutions previously without modern equipment.
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From page 15... ...
These data have shown, for example, that the transformfault hypothesis, which predicts a direction of relative motion along ocean fracture zones exactly opposite to that of the conventional interpretation, is indeed correct. A key finding in the problem of the driving mechanism of the plate motions came from a comprehensive study of the focal mechanism of the intermediate and deep earthquakes in island arcs throughout the world.
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From page 16... ...
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From page 17... ...
Free oscillations of the earth have been detected and their characteristic frequencies measured from the spectra of WWSSN recordings even at periods as long as l500 sec. These oscillations are largely unaffected by local structure, so that observations of their spectral energy distribution gives information about the radial distribution of elastic parameters and density with depth, averaged over the whole earth.
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From page 18... ...
The WWSSN has continued to provide data for numerous studies of geologic phenomena within the earth, particularly for those studies that bear on the seismicity of the earth and on its temporal variations. These studies are vital, moreover, to our understanding of the serious earthquake hazard confronting a large portion of our nation, and the need for this understanding grows as the nation's population density and the complexity of society grow (see Figure 7)
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From page 20... ...
granted partial, but crucial, support to the foreign segment of the network. Through l972, NSF continued its partial support of the network at an annual level of $283,500, and ESSA supported 3l stations operated by domestic agencies at a comparable level.
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From page 21... ...
In spite of the fact that 75 percent of the WWSSN stations have not been visited in the last five years for calibration and maintenance, the network has, surprisingly, managed to survive and to continue to serve as a primary data source for seismological research. But the inevitable progressive deterioration of record quality to be expected under such conditions is now becoming apparent.
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From page 22... ...
to provide suitable data organization, storage, retrieval, and distribution facilities. We estimate that funding in the amount of not less than $860,000 per year will be needed.
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