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DC Spectral Ordinates

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Please Help!

I am working on a seismic analysis in Washington DC.  The MCE maps from FEMA-302 give me values of Ss =.14 and S1 = .07 for the site.

What confuses me is that TI-809-04 (which I must use) says that you can convert UBC Zones to S1 and Ss, and doing it the way they describe, I get Ss = .31 and S1= .14 for Zone 1.
These two methods of getting the numbers are so different that I am not sure which to use, it seems to me the maps give the more realistic values, can somebody PLEASE help me?