[Shake-dev] intensity bias in ShakeMap v3.5

[Georgia Cua]

Dear Bruce, shake-dev,

I have been working on our ShakeMap v3.5 installation in Switzerland.

I noticed something peculiar with the behaviour of the intensity bias.

I have the observed PGA and PGV from a M3.3 in Switzerland. (To be safe, I used Small as the GMPE and Wald99 as the GMICE. The behaviour is similar when I use our Swiss-specific GMPE and GMICE.)

When I run this event with the observed PGM as input, there are large bias values for PGA and PGV, -1.5 and -0.7. (Those are expected, as PGA and PGV in Switzerland tend to be lower for a given magnitude than predicted by California relationships.) What troubles me is that the intensity magnitude bias turns out positive (1.43). 

If I run a shakemap for this event without the PGM as input (just providing the event.xml file), the maximum intensity is 3.64. When I run it with the PGM as input, the maximum intensity is 5.1, even though the PGA and PGV biases are both negative. 

I've run this same event on our v3.2 installation, and there, it seems to behave as I expect, where if the PGA and PGV biases are negative, the maximum intensity using the PGM observations will be lower than when running it without the observations.

I am attaching the message logs from running shake, grind.conf, the info.xml file, as well as the regression plots.

I am not sure where I am going wrong. Thanks in advance for your help.

Georgia

PS. When there is no native intensity data provided as input, and no IPE is specified, should the intensity bias still calculated? 
















-----------------------------
Dr. Georgia Cua
Swiss Seismological Service
Institute of Geophysics
ETH Zurich, NO H61
Sonneggstr 5
CH-8092 Zurich
Switzerland

Tel:  +41-44-633-7574   
Fax: +41-44-633-1065   

georgia.cua at sed.ethz.ch
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