Correlation Study of Shear Wave Velocity in near Surface Geological Formations in Anchorage,Alaska

In the summer of 1995, surface measurements of shear wave velocity (β) was conducted at thirty six sites, approximately, in the 0-50 m depth range. Of these, at seven sites values of β, soil log and blow count (N) from borehole measurement were available from previous investigations by others. Using these seven sites for calibration, we compared the velocity profiles yielded by the surface and borehole measurements for these sites. The results show broad similarities. Using the soil logs and shear wave velocity variations at the seven sites, four site classes (SC-Ic, SC-II, SC-III and SC-IV) could be identified. The surface method corresponding to the mean value of β tends to underestimate β between about 1 and 18 percent for site classes SC-Ic, SC-II and SC-III compared to the downhole method. For SC-IV, β is overestimated by 11 percent using surface method. Moreover, the blow count (N) data for each site class shows a linear relationship with β obtained by the surface measurement.