This storm dumped a pile of boats off their cradles at the marina next door
to Crosswinds in Whitehall, MI:

http://www.msu.edu/~fujita/tornado/l...rr-report.html

An explanation fro U of M:
http://www.seismosoc.org/publication...l_69-5_eq.html

Make sure you read all of it:
http://www.crh.noaa.gov/dtx/wxnow/pr...FNT.0312022331