The event based calculator should generate ses_collections only according to the source_model logictree, not the GMPE logic tree

[Michele Simionato]

At the moment, if there is a single source model and 3 GMPEs in the logic tree file we are generating 3 ses_collection outputs which are identical. That makes no sense. The calculator should not need the GMPE logic tree file at all when generating SES only, the GMPEs are only needed for the GMF calculation.

[Michele Simionato (michele-simionato)]

https://github.com/gem/oq-engine/pull/1336

[Michele Simionato (michele-simionato)]

The PR https://github.com/gem/oq-engine/pull/1336 was closed because of potential issues with the GMF-on-the-fly feature; however now that the feature is going to be removed it has become possible: see https://github.com/gem/oq-engine/pull/1365