The goal of this project is to evaluate shear wave velocity (Vs) profiles at approximately 15 sites in the Los Angeles, CA area using noninvasive, surface-wave seismic technology. The results of the Vs profiles will fulfill three purposes. First, at many sites, new information will be generated for PEER Lifelines Task 2G01 where profiles to depths in excess of 30 m would be beneficial. Second, some sites will be drilled and logged in the future under PEER Lifelines Task 2A01. The Vs profiles will be used in “blind” comparisons with subsequent profiles measured with the suspension logger. Third, some sites have “old” Vs profiles; that is, Vs measurements performed by other seismic test methods. The new Vs profiles will permit evaluation of the validity of the older data.

One of the key parameters involved in evaluating the performance of soil and rock sites during earthquake shaking is the in-situ shear wave velocity (Vs) profile of the site. This profile is used to calculate the initial small-strain stiffness of the geotechnical materials before shaking commences. Analytical modeling is then used to estimate the nonlinear response of the site during each earthquake. The results from this project (shear wave velocity profiles at SMA sites) assist in understanding and quantifying the impact of ground motions that have been measured at strong-motion recording sites. Further, the results are needed in the refinement of ground-motion attenuation relationships which are essential in predicting damage from future earthquakes.

The seismic-testing methodology used in this field study involves noninvasive testing with Rayleigh-type surface waves. The testing technique is called spectral-analysis-of-surface-waves (SASW) testing. This technique is noninvasive, with all equipment placed on the ground surface. In this project, a large, one-of-a-kind drop weight was used as the primary seismic source. This drop weight was specially selected for use in the Los Angeles urban environment so as to cause little to no impact (disturbance) yet profile to significant depths. With this equipment, robust Vs profiles to depths of 30 to 45 m were evaluated at stiff soil and rock sites (but not soft soil sites). The main constraints on the number of sites that could be tested were:

1. the site preparation time
2. the travel time between sites, and
3. the depth of penetration.

Completed measurements of in-situ Vs profiles at 16 selected strong-motion recording sites to depths on the order of 30 to 45 m. The work was coordinated with the ROSRINE 5b Project and Prof. Robert Nigbor (PEER Lifelines Task 2A01). The work was also coordinated with Professor Stewart of UCLA because of his efforts on developing calibration sites for the validation of nonlinear sites-response codes, PEER Lifelines Task 2G01, Phase A.

No other similar work is being conducted within or outside PEER at this time.

Project will be completed by 31 July 2003.

Dr. Cliff Roblee and Dr. Walt Silva are presently using the preliminary results (as well as the results from 30 sites in Imperial Valley, CA) in site response studies.

Completion of data analysis on 31 May 2003.

Digital and hard copies of report on 31 July 2003.