Adding M9 Seattle Basin Adjustment + Campbell and Bozorgnia (2014) basin term to ModifiableGMPE capabilities #10118
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micheles
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Nov 5, 2024
micheles
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Nov 5, 2024
CB-quakemodel
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This PR adds the M9 Basin adjustment and the Campbell and Bozorgnia 2014 basin term to ModifiableGMPE.
The M9 basin adjustment is an additive factor to the mean ground-motion for long period spectral accelerations (T > 1.9 s) of + log(2.0) for all sites with z2pt5 greater than or equal to 6 km for interface sources within the Seattle basin applied in the US 2023 conterminous hazard model.
The M9 basin term is applied in the US 2023 interface GMC for sites in the Seattle Basin. The adjustment is made to the ZhaoEtAl2006SInter, AtkinsonMacias2009, ParkerEtAl2020SInterB (basin version) and KuehnEtAl2020SInter GMMs. The M9 basin adjustment is not applied to AbrahamsonGulerce2020SInter (which uses the US adjustment factor).
The US implementation of the M9 basin adjustment is conditional upon the pre-basin amplification mean + the M9 basin adjustment being greater than the pre-basin amplification mean + the M9 adjustment (pp. 1178 of Moschetti et al. 2024). This does not apply for the AtkinsonMacias2009 and ZhaoEtAl2006SInter classes because they do not have their own basin terms (for the non-M9 versions they use the CampbellBozorgnia14 basin term, thus the adding of this basin term to ModifiableGMPE here too).
The PR adds the following:
A separate ModifiableGMPE class (as exists for example for CY14 site term and NRCAN15 site terms) for both M9 basin adjustment and the CB14 basin term. Having a separate ModifiableGMPE class for M9 and CB14 basin terms with importable basin adjustment gives us flexibility depending on how we implement these adjustments within the OQ gsims too.
The ability to specify the M9 basin adjustment or the CB14 basin term as a kwarg when instantiating a ModifiableGMPE from a GSIM LT XML (or programmatically), like any other ModifiableGMPE capability such as the Al Atik 2015 sigma model.
Some simple unit tests. For the M9 basin adjustment, these are checking that the basin adjustment is only applied for long period ground-motions at sites with z2pt5 > 6 km, with an expected different of log(2.0) being obtained at these sites compared to the values obtained at the same sites with the unmodified version of the same GMM. For the CB14 basin term, these are checking that the expected results are obtained for cases in which the adjustment is not applied, and the case that it is applied either through the CB14 basin term ModifiableGMPE class, or as a keyword when instantiating a generic ModifiableGMPE.
Some example plots are provided here showing the M9 adjustment factor for the KuehnEtAl2020SInter and ParkerEtAl2020SInterB GMMs for an interface event with focal depth of 40 km, vs30 = 500 m/s and z2pt5 = 6 km:
Some example plots are also provided showing the impact of the CB14 basin term when applied to the AtkinsonMacias2009 GMM:
T > 1.9 s threshold for M9 term is confirmed by usgs java code (e.g. line 205 of https://code.usgs.gov/ghsc/nshmp/nshmp-lib/-/blob/main/src/main/java/gov/usgs/earthquake/nshmp/gmm/AtkinsonMacias_2009.java?ref_type=heads).
The US 2023 GMM adjustments are preliminarily discussed here too for reference - #9894