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# Seismic Maximum Considered Earthquake Geometric Mean PGA Maps

## Seismic Maximum Considered Earthquake Geometric Mean PGA Maps

(OP)
Referring to ASCE7 seismic maps, specifically ASCE7-10 figure 22-7. Are these maps based on a 1% exceedance in 50years (5,000 yr return)? I'm trying to understand the difference between the variable "PGA" when referenced in ASCE7 vs AASHTO and I beleive the difference is the return period, but the probability is not listed on these figures. I assume they are the same as others, but I might off entirely.

ASCE7 PGA = mapped MCE (Maximum considered earthquake) peak ground acceleration (not sure what the return period is)

AASHTO PGA = Horizontal peak ground acceleration coefficient (with 7% probability of exceedance in 75 yr, 1000year return)

In general the ASCE7 PGA is higher than AASHTO which would make sense if the return period is 5,000 years.

Thanks

### RE: Seismic Maximum Considered Earthquake Geometric Mean PGA Maps

The ASCE 7-10 Commentary says Figure 22-7 uses a 2% in 50 year exceedance.

Go Bucks!

### RE: Seismic Maximum Considered Earthquake Geometric Mean PGA Maps

(which, to save you the math, is described as a 2475yr return)

----
just call me Lo.

### RE: Seismic Maximum Considered Earthquake Geometric Mean PGA Maps

(OP)
Thanks for the info. I also missed it in Ch 21.5. I really air-balled this. Thanks again.

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