OFR14-01, Evaluation of the horizontal-to-vertical spectral ratio (HVSR) passive seismic method for estimating the thickness of Quaternary deposits in Minnesota and adjacent parts of Wisconsin

Chandler and Lively of the Minnesota Geological survey have published an excellent paper on Tromino Passive Seismic surveying for characterizing quaternary cover thickness. Worth a read if you're interested in the topic! Available from UMN website by clicking the below link.
http://conservancy.umn.edu/handle/11299/162792