Preliminary Shear-Wave Velocity Profiles of Deep Soils (Depth > 600 M) in the Mississippi Embayment, USA

Session: Near-Surface Effects: Advances in Site Response Estimation and Its Applications [Poster]
Type: Poster
Date: 4/28/2020
Time: 08:00 AM
Room: Ballroom
Description: 

As part of a detailed seismic hazard mapping project in 5 western Tennessee counties sponsored by the U.S. Department of Housing and Urban Development (HUD), we use the spatial autocorrelation (SPAC) method to estimate shear-wave velocity profiles at 5 deep soil sites in or near Lake and Dyer counties, TN. In this area, the Mississippi Embayment is a southwest plunging synclinal trough of unconsolidated and poorly consolidated sediments overlying a hard-rock basement ranging in depth from 600 to 844. From ~15 hours of ambient ground motion recorded at each site on a temporarily deployed linear array of 5 broadband seismometers with interstation distances ranging from 20 to ~400m, we calculate the mean and standard deviation of the SPAC coefficient as a function of frequency and distance for each station pair. From this set of SPAC curves, a shear-wave phase-velocity curve from ~0.3 to 5 HZ is generated (based on Aki’s formulation for Rayleigh waves) for that site. We then invert the phase velocity curve for a smoothly varying 11-layer over hard-rock half-space velocity model where layer thickness and starting velocity are consistent with lithological units identified from analysis of shallow and deep well logs performed in the geological part of the HUD project. The average shear-wave velocity for the sediment package ranges from 650 to 675 m/s for these sites.

Presenting Author: Stephen P. Horton

Authors