Correlations Among Seismic Velocity,Depth and Geology in the Los Angeles Area,

摘要

Correlations among seismic velocity,Poisson's ratio,depth,and a geotechnical classification scheme was developed from 63in-situ velocity measurements in the greater Los Angeles area. Average shear-wave velocities at the surface for 11soil and geologic materials were found to vary from about 500ft/sec for unconsolidated soils to about 3900ft/sec for fractured basement complex. A preliminary estimate of Poisson's ratios for the near surface yielded values of approximately 1/4for compacted fill, 1/4for rock, 1/3for soil above the water table,and 1/2for soil below the water table. The functional relationship between shear-wave velocity and depth was found to be adequately given by Vs = Kdn between depths of 10and 100feet,approximately,where the constants K and n are dependent upon the geotechnical classification. The correlations were used to estimate low-strain shear and P-wave velocity profiles at two sites in the Los Angeles area for which velocity data were available but had not been used to establish the correlations. The good agreement between the estimated and measured velocities at the two sites suggests that the correlations may be used in establishing synthetic near-surface velocity profiles from shallow geotechnical data when actual velocity data are unavailable.