San Mateo county, 3rd floor of early 1990s office building, built on slab foundation on deep piers driven into former salt evaporater / dried out bay mud. Felt two rollers, enough to rattle windows but not enough to cause building to creak and groan. Was on con call w/ folks in Alameda County who said they did not detect it. Some newbies were freaking out and running into hallway. That's about it.
Preliminary Earthquake Report
California Integrated Seismic Net
USGS/ Caltech/ CGS/ UCB/ UCSD/ UNR
A moderate earthquake occurred at 17:19:07 (UTC) on Tuesday, September 28, 2004. The magnitude 5.0 event has been located in CENTRAL CALIFORNIA. The hypocentral depth was poorly constrained. (This is a computer-generated message -- this event has not yet been reviewed by a seismologist.)
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Keep in mind that those piers are supposed to be driven deep enough to go through the mud and into the solid rock below.