# Magnitude-Scaling relationships

23 views

### ariascr...@gmail.com

Jun 10, 2021, 7:37:39 PMJun 10
to OpenQuake Users

Hello,

I wonder why in a PSHA simulation if I use a discrete incremental magnitude frequency distribution and if I use a double truncated Gutenberg-Richter distribution, assuming both represent the same magnitude frequency distribution, I am obtaining bigger PGA's in the first case than the second one. I think I must to have the same results in both cases.

To give a context I am using the following data.
• <truncGutenbergRichterMFD aValue="2.688350" bValue="0.635628" maxMag="8.7" minMag="6.0"/>

• <incrementalMFD minMag="6" binWidth="0.1">
<occurRates>0.074917279795517
0.064717122631906
0.055905739946577
0.048294046951857
0.041718703181764
0.036038607344361
0.031131869407887
0.026893194944209
0.023231625599843
0.020068587206946
0.017336203648424
0.014975840294109
0.012936845751408
0.011175464929441
0.009653900091958
0.008339499750027
0.007204057988816
0.00622320919262
0.005375905179447
0.004643963524909
0.004011677382841
0.003465478429724
0.002993645699988
0.002586054064048
0.002233956951621
0.00192979865776
0.001667052203845
0.001440079274161
</occurRates>
Thanks regards.

### Marco Pagani

Jun 11, 2021, 1:57:24 AMJun 11
to OpenQuake Users

Because your MFDs are not exactly the same. From OQ manual page 38 “A discrete incremental magnitude-frequency distribution: It is the simplest distribution supported. It is defined by the minimum value of magnitude (representing the mid point of the first bin)”. On the contrary the mmin for a double truncated is the lowest magnitude i.e. when you discretise it the mmin corresponds to the lower limit of the first bin (see also Fig. 2.5 and 2.6)

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### UWIDUHAYE Jean d'Amour

Jun 11, 2021, 12:44:54 PMJun 11
to OpenQuake Users

I have a problem with my plugin when once tried to download or once tried to connect to openquake platform.
I am using Qgis 3.16 long release.

Kind regards,

Jean d'Amour U.