Methodology for correcting spectral ratio absorption estimates for source wave travel paths in DST

Downhole Seismic Testing (DST) is utilized for estimating low-strain shear damping ratio (ηs). Estimates of low strain s η values are very important for predicting and assessing ground amplification during earthquakes. The low strain ηs estimates also provide for a reference of laboratory tests such as the resonant column test. The Spectral Ratio Technique (SRT) is one of the most utilized analysis techniques for processing seismic data to obtain ηs. The SRT is applied in the frequency domain where the spectral ratio of two data sets and relative arrival times are calculated to obtain the quality factor. The quality factor is inversely proportional to the damping ratio. One of the limitations of the SRT is that it doesn’t account for the raypaths of the source waves. In DST the raypaths are of particular importance due to the fact the source waves will refract as they travel from the surface down to the seismic receiver. This paper outlines a technique, so-called FMDSM-SRT, which facilitates adjusting estimated SRT absorption DST values so that source wave raypaths are accounted for. It is of paramount importance to first implement newly optimal estimation algorithms on extensive test bed simulations prior to processing real data sets. This paper outlines the results from processing a challenging test bed simulation with the FMDSM-SRT algorithm.