Site Effects on Power Spectral Densities and Scaling Factors.
Abstract
This study presents the results of a statistical analysis of the spectral shapes of power spectral density (PSD) functions, G(omega), in the 0.006- to 10-Hz range for 421 horizontal ground accelerograms (all records processed to the same duration of 163.83 sec, i.e., 1/163.82 = 0.006 Hz) from 89 earthquakes, mostly in the western United States and Japan. The analysis shows clear differences in spectral shapes for different soil and geological conditions. Within the high-frequency range of 2.5 to 10 Hz, the spectrum for the rock sites contains the highest energy or intensity; the spectrum of the stiff soil sites is slightly less than for the rock sites; and the spectra of the soft clay and sand sites and the deep cohesionless soil sites are almost the same and are lower than those for stiff soils. However, in the low-frequency range of 0.006 to 2.5 Hz, the reverse exists: the soft sites indicate the highest energy, the deep cohesionless soil sites are next, the stiff soil sites are third, and finally, the rock sites. A qualitative comparison was made on the spectral shapes of the PSD calculated in this study with the acceleration response spectra (ARS) of Kiremidjian and Shah (1978), Seed and Idriss (1971), and Seed, Ugas, and Lysmer (1976). There is general agreement in the shapes of both types of spectra, except the relative amplitudes for the rock sites for the ARS were less than those of the PSD in the high-frequency range. The average and average plus one standard deviation power density spectra functions for different site conditions have been normalized to a unit area.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 1981
- Accession Number
- ADA102899
Entities
People
- Frank K. Chang