While I do not claim to be a seasoned EQ engineer, I looked at this, and while it is hard to follow since ASCE 7-05 is in a new format, I believe that Eq.15.4-4 is intended to replace the Cs min equations 12.8-5 and 12.8-6, which also use S1. I believe that the R values from Table 15.4-2 are to...