Seismic Ground Motion Parameter Relations

The relationships among spectral velocity for 0.5 hz and 1.0 hz frequencies, peak ground acceleration, and peak ground velocity of earthquake-induced ground motion are investigated using the horizontal components of motion from 70 California strong-motion records and accounting for event size, source-to-site distance, and geologic conditions at the recording site. These strong motion records indicate that the estimation of intermediate-frequency spectral response using ground acceleration and typical design spectra is unconservative for a large, distant event (magnitude-8+, 120-km epicentral distance) by a factor of about 2 to 6, depending on the site geology. Ground velocity can be used to estimate intermediate frequency spectral response; however, expected spectral response will exceed these estimates during the motion from large, distant events by a factor of about 1.4 to 2.5. Because of the large variabilities associated with strong motion data, these results are tentative.