They've put up more info:
http://www.ldeo.columbia.edu/LCSN/Eq/20010911_wtc.html
"Notice the seismic signals from the first impact at 08:46 EST, second impact at 09:03 (very small), two large signals due to collapse of the World Trade Center buildings at 09:59 and 10:28 (EST). We understand from news reports, that the first impact (0846 EST) resulted in the second collapse (1028 EST), and the second impact (0903 EST) resulted in the first collapse (0959 EST)."