using a combination of GMPEs

[Hyeuk Ryu]

Hi,

I noticed that the OQ engine does not yield any informative warning message to user when non-compatible GMPES in terms of requirement of site parameters are used together, such as Somerville 2009 and Akkar_Bommer 2010. For the reference, Somerville 2009 is calibrated for vs30 = 865 m/s, and does not require vs30 for site parameter while Akkar Bommer requires vs30. When either reference_vs30_value or site_model_file is defined in the job.ini file, it does not affect Somerville 2009 at all because it does not require vs30. So the simulated ground motions are not the same in terms of the site condition. I would like to see the engine to yield a message informing user of the issue at least.

Also wonder if there is any plan to implement a generic site model such as Seyhan Steward 2014 to be combined with any GMPE with no site model. For instance, I made some changes to Somerville 2009 as attached to include site effect (SomervilleEtAl2009NonCratonicSiteModel), but having an option of combining of a site model with any GMPE seems useful to user.

Thanks.

Regards,

Hyeuk

[Graeme Weatherill]

Dear Hyeuk,

I understand the issues you raise and it could be interesting to hear others' feedback on this first one. I can't speak on behalf of the GEM development team, but personally I have always been cautious about throwing even warnings related to issues with the GMPEs when they are not actually a computational problem in execution but rather a theoretical problem in the selection. One reason is that there are simply so many combinations of GMPEs that should not be used together, as well as various degrees of incompatibility, that implementing the various checks and throwing meaningful warnings can end up becoming a surprisingly large task.

Regarding the site model issue, there is work under way in this direction, albeit in the early stages, to add more capability to OQ to handle different user defined site amplification models and their uncertainties. The one you highlight is noted, as are others. At this point I can't pinpoint a particular date or release for which we plan to have these features, as this will depend a lot on the requirements and the complications/challenges that arise, to say nothing of the time pressures on GEM staff and OQ contributors in 2018, so for now all I can say is that it is now it is on the table and that we're looking into it.

Thanks,

Graeme

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