TEXAS INSTRUMENTS INC DALLAS
Pagination or Media Count:
Worldwide seismic noise levels and characteristics for 1963 are discussed. Data for evaluation includes absolute power density spectra and contour maps of average worldwide microseismic activity. Relative power density spectra were computed from 1963 from Worldwide Standard Stations. Slopes of the least-mean-square line through the power density points were computed and a pattern of slope changes appeared at a frequency of 1.0 cps. A uniform worldwide pattern of slopes was observed between 1 cps and 2 cps. This suggests two separate sources generating microseisms above and below 1 cps, respectively, and that the spectra above 1 cps are independent of storms, fronts, etc. The spectra for frequencies less than 1.0 cps show greater seasonal variations. These were concluded to be mostly meteorological in origin. Monthly contour maps of average noise show that noise is seasonally variable and that it is attenuated at continental structures.