I was doing some looking around and found out that time discrepancies can and do happen in siezmic data.
According to this site the LDEO uses the CNG-5TD strong motion accelerometers.
http://www.ldeo.columbia.edu/LCSN/intro.html
According to thier data sheet:
http://www.ldeo.columbia.edu/LCSN/News/CMG-5TD_rev2.pdf#search="CMG-5TD"
The sensors use GPS time not UTC. (See page 15 in the link to the manual for proof that the sensors are synced to GPS and not directly to UTC)
And there is a 13 second time difference between GPS and UTC.
According to NIST who oversees UTC :
http://tf.nist.gov/service/acts.htm
"GPS time differs from UTC by the integer number of leap seconds that have occurred since the GPS time scale begam on January 6, 1980. This difference equaled 13 seconds at the end of 2004.The integer-second difference is included in the GPS broadcast message, and is
usually applied automatically so that GPS clocks display the same hours, minutes, and seconds as UTC clocks." (that is unless somebody makes an error in setting up the equipment)
Here's the manual for the CNG-5TD:
http://www.ldeo.columbia.edu/LCSN/News/CMG-5TD_Manual_rev_B.pdf#search="CMG-5TD"
on page 21 you see a statement that the synchonizaton to a time standard has to selected.
So there is a possiblity that an installer may have set a wrong option. and the time discrepancy deemed incosequential because the relative difficulty or distance in returning to the sensor site.
As a matter of fact this does occur at times.
This report shows that a systematic timing drift can occur in the CNG-5TD if a power setting in the GPS reciever is incorrectly set.
http://www.ess.washington.edu/SEIS/PNSN/REPTS/Quarterly2003A.pdf#search="CMG-5TD problems"
See page 3 paragraph 3
http://www.ldeo.columbia.edu/LCSN/Eq/20010911_WTC/WTC_LDEO_KIM.pdf
The chart shows UTC, but the sensors use GPS. So there had to be a conversion going on; probably in the software used to analyse the data.
And if is a timing drift going on in the sensor you will get a time discrepancy. I'm not saying that is what happened. But there is a definit possibility for it to happen