In Situ Shear-Wave Velocity Assessment at the Delaney Park Downhole Array, Anchorage, Alaska

The shear-wave velocity (VS) in soil is an important parameter to characterize dynamic soil properties. The Delaney Park downhole array was deployed in 2003 without measuring the shear- and compression-wave velocity (VS and VP) profiles. Thornley et al. (2019) measured the VS and VP profiles using the downhole method after the sensor was removed from the 61 m borehole with casing in the array. However, the waves propagating along the casing wall may have a great influence on the recognition of the first arrival of waves propagating in the soil. Using horizontal and vertical components of weak-motion data of eight local earthquakes recorded by the array, in situ VS and VP profiles were assessed by the seismic interferometry based on deconvolution, respectively. The results are as follows. The VS and VP profiles computed by this study and measured by Thornley et al. (2019) are in relatively good agreement at a depth of 10–45 m and at a depth of 30–45 m, respectively, and in very poor agreement at other depths. The average VS profiles computed by this study are more consistent with the derived VS from the standard penetration test data at the site with slower near-surface velocities relative to the downhole logging analysis. There are strong anisotropy in the strata below 45 m and weak anisotropy with various degrees at various depths in the strata above 45 m.