|This ongoing investigation is attempting to greatly expand the worldwide data-set of shear wave velocity characteristics of liquefaction sites, most of which are in Asia. Doing so will allow for a re-evaluation of the liquefaction boundary curves presented in the literature with a new data set rich in high shear wave velocity and high ground motion intensity locations.
The Spectral Analysis of Surface Waves (SASW) method is a relatively new non-invasive approach for evaluating the shear wave velocity characteristics of potentially liquefiable ground. In our test procedure, we array small-lightweight sensors on the surface and collect vibrations produced with a small frequency-controlled electro-mechanical shaker. SASW is particularly useful for lightweight reconnaissance surveys and profiling difficult materials such as gravelly sand where conventional truck-based penetration methods are not practical. The dispersive nature of surface waves serves as the basis of the SASW method. After we have recorded the dispersion characteristics of surface waves at a site, we utilize the Haskell-Thompson inversion technique to estimate the shear wave velocity profile. Then, the velocity of the observed liquefied layer, a 'Resistance' term related the stiffness properties of the ground, is compared with the estimated 'Load' of the earthquake motions at the site. In 'Load-Resistance' space we can identify the zone where liquefaction occurs
In Japan and Taiwan, we profiled 182 liquefaction test sites using this method, producing detailed shear wave velocity profiles in the upper 20-30 meters of the soil column. Testing is planned for Chinese sites in 2003. Nearly all of the documented liquefaction sites in the Japan and Taiwan from 1948 on, that were evaluated with conventional penetration apparatus, were re-tested in our study. These liquefaction events, dating from the most recent large events in Japan and Taiwan (2001 Geiyo and 1999 Chi Chi, respectively), back to the 1948 Fukui City earthquake, represent the majority of the worlds documented sites of liquefaction occurrence. The data from this study allows us to recast the shear wave velocity-liquefaction correlation in light of a global data set.