INVESTIGATION OF SHORT-PERIOD SEISMIC NOISE IN MAJOR PHYSIOGRAPHIC ENVIRONMENTS OF CONTINENTAL UNITED STATES
Final technical rept. for 1 Sep 1961-31 Dec 1964
MICHIGAN UNIV ANN ARBOR INST OF SCIENCE AND TECHNOLOGY
Pagination or Media Count:
Measurements of spectral density levels of shortperiod seismic noise are obtained for points distributed throughout the continental United States and for a few non-North American locations. Noise amplitudes and gradients in the far field correlate on a regional basis with major physiographic provinces, as revealed by iso-particle-velocity contouring. The ensemble of space and time samples of noise is examined to illustrate the average spectrum and dispersion for three orthogonal components of ground-particle velocity in the range 0.25 to 100 cps. Probability distributions of noise amplitudes based on a collection of space averages and time averages are presented for several frequencies. The ratio of horizontal to vertical noise amplitude HZ exceeds the theoretical value for simple Rayleigh waves and shows a frequency-dependent variation with regional geologic environment.