i suggest using the lat/lon feature of that...it makes a fairly significant difference at times. also be on the lookout in the next year or so of the revised maps (preliminary maps can be found on the usgs website at
the values will be adjusted down in a lot of areas and up in a few high seismic areas. it might be very beneficial to your clients if you are aware of what is coming.
i'd also suggest becoming familiar with the ways to evaluate the site class using shear wave velocity. in my area, the spt value method for determining site classificaiton is pretty conservative versus the shear wave method. in other words, the shear wave provides a more refined evaluation of the site classification to determine Fa and Fv. if you have a good geotech, they can provide guidance regarding whether the spt values appear good enough for the shear wave to make a difference.
Please do not use the zip code, you must use the lat and long to get accurate information. I checked some designs where the structural had used a zip code and the values where more than 20 percent to low, not a good thing. The location given by the zip code was more than 14 miles from the actual site.
also be on the lookout for folks using the wrong maps. some states adopted the more recent ibc/usgs maps while the permits were under the '03 code...since the maps changed in between that period, the values were off high by 20%+ (changed the SDC). this is sort of the scenario that will likely happen again based on my first post above since the maps have been updated and will be adopted "very soon" (in next year or so...maybe it will hold off until the IBC'09 comes out in jan '10--i think that's when the next cycle is completed).
