PSBAH20 epistemic uncertainty model

Implement Parker et al. 2020 epistemic uncertainty model and output a 3-branch logic tree of GM

See #129 (closed)

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• 369707d9 - update Parker et al results (weighted sum of epistemic branches)

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New test results accepted as is (not re-generated from external code)

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marked this merge request as ready

This MR had conflicts after merging AG20 changes; the changes to the interface results for PSHAB need to first be rebased against changes from !217 (merged). Also, this MR should include updates to the slab test results.

added 23 commits

• 369707d9...47b15135 - 20 commits from branch ghsc/nshmp:main
• cdac926b - clean up
• b0373866 - add PSBAH20 epistemic uncertainty, outputs 3-branch logic tree with NGA-West2 weights
• da2e881b - update Parker et al results (weighted sum of epistemic branches)

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added 1 commit

• bb7e427a - update Parker et al slab results (missed previously)

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mentioned in commit 49268c6f

merged

mentioned in issue #129 (closed)