Magnitude-weighting

[Jenni Tipler]

Hi,

Will OpenQuake allow me to apply a Magnitude-Weighting relationship? In creating the New Zealand seismic spectra, GNS typically applies magnitude-weighting for periods up to 0.5s by applying a factor equal to (M/7.5)^1.25 to the spectral acceleration values. 

Kind regards,

Jenni 

[Graeme Weatherill]

Dear Jenni,

Unfortunately OpenQuake does not have that sort of functionality built in, though potentially it might be possible to customise it.

I am not sure I have understood the magnitude-weighting correctly, though. Does magnitude-weighting apply to the mean values of the GMPE, or is it some correction factor that is applied in some other context (e.g. scenario spectra)? If it is the former then this can be added quite quickly as an adaptation of an existing GMPE (though we need to know which, e.g. McVerry et al. 2006?), if it is the latter then this is something that should be done as a post-processing step.

Let me know and I will see if it is possible to provide a bit more detail on how to solve the problem.

Regards,

Graeme

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[Jenni Tipler]

Graeme,

Thanks for the reply. Yes, it's applied to the mean SA values for periods between 0 and 0.5 seconds. The GMPE will be the three McVerry ones you have in Openquake but I'd need to see the weighted and the unweighted results because the weighted results seem to apply to design spectra for structures and the unweighted results are needed for the geotech design. I think that the factor is intended to account for the shorter duration of smaller magnitude earthquakes and the longer duration of large magnitude ones. 

Currently Im running open quake on the OATS server. If I wanted to customize the GMPEs I assume id need to use the desktop version, correct?

Jenni