Can the DSHA spectrum be less than the PSHAs spectra?
I came across a report with the attached graph showing DSHA curves from each source considered in the PSHA calculations are less than the spectral values for the PSHA curves with 1000 and 2500 return year periods.
My understanding was that since DSHA is deterministic, it represents the worst-case scenario, and the spectral acceleration using this method will be greater than that of PSHA.
It is certainly possible. Prof Jack Baker has this discussed in his book. He also has one of the example showing DSHA represent a "non-worst" case.
You can access his simplified notes here:
https://www.jackwbaker.com/Publications/Baker_(2008)_Intro_to_PSHA_v1_3.pdf
I believe this is discussed in chapter 1.2.
Hopefully this helps,
Regards,
Steve
Hi Arman
I confirm the previous answer by Zhongze Xu / Steve. It also depends on the way the DSHA spectrum is computed, i.e., how the aleatory variability σ of the GMPE is taken into account ( 0 σ, 1 σ, ...)
Best regards
py
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