According to a seismographical study conducted by Columbia University’s Lamont-Doherty Earth Observatory in Palisades, New York, five distinct shocks occur at the World Trade Center site. They occur at 11:01 a.m., 11:15 a.m., 11:29 a.m., 12:07 p.m., and 12:10 p.m. According to the study, the five resulting seismic signals “may have been generated by additional collapses.” [Earth Institute at Columbia University, 11/16/2001; Kim et al., 11/20/2001
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