Can you find the site class from the PGA or the Mapped Acceleration Parameters?

[CDG31]

Hi,

I am wondering if the site class can be identified from the PGA for a specific site or the site Mapped Acceleration Parameters Ss or S1? If so, how?

Thanks,

 

[driftLimiter]

ASCE 7 - 16 has Ss and S1 contours for the US. You can look up the values from multiple locations on the web including: [URL unfurl="true"]https://seismicmaps.org/[/url]

However the Seismic Site class must be determined from the soil parameters or assumed, it cannot be looked up.

 

[CDG31]

I got asked a question recently that just threw me off. The question was three lines long,

PGA = 0.3
S1 = 0.9 (I think S1 was 0.9, but I don't recall exactly what the value was)
Find PGAm?

I know PGAm can be found using section 11.8.3 from ASCE 7-16 but the factor Fpga, is based on the site class not S1. Thus, I got confused on how to find PGAm. I am not sure if you have any comments that could help me solve this question.