Truncated GR mfd

[disotiri1]

Dear all,

I tried to compare some PSHA results by using the truncated GR MFD and the incremental MFD.  

To calculate the incremental MFD rates I used the so called "bounded Gutenberg-Richter recurrence law", that is equation (4.10) from the book of Kramer (1996) "Geotechnical Earthquake Engineering". 

I believed that the same law was used for the truncated GR MFD in Openquake, however, within the truncated_gr.py script, I noticed that the rate, at a specific magnitude bin, is calculated as:

rate=10 ** (a_val - b_val * mag_lo) - 10 ** (a_val - b_val * mag_hi),

where mag_lo is the minimum magnitude of the bin and mag_hi is the maximum magnitude of the bin. 

The rates calculated by the above equation and equation (4.10) in the book of Kramer, when using the same a- and b-values, are completely different, hence, the results between the two PSHAs differ substantially. 

So, my question is if I have misundersatnd somethng regarding the implementation of the trucnated GR MFD in openquake and also if the aValue and bvalue in the truncated GR MFD are somehow related to the ones of equation (4.10) in the book of Kramer. 

Best regards,

Dimitris

[Marco Pagani]

Eq. 4.10 in Kramer gives you the rate of exceedance of m. I don’t understand how you can compare its results with the ones of the equation in your email (which gives you the rate of occurrence within a magnitude bin)

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MARCO PAGANI | Seismic Hazard Team Lead | Skype mm.pagani | +39-0382-5169863

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