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dear Marc
in the linear FK toolbox in the tab "curve" there is an indication for the maximum wavelenght reach in the interpretation of dispersion curve. we can draw a line for a constant wavelenght.

do you think that the iso-wavelenght line Lambda 40, could be used for the estimation of the VS30 as is proposed by Martin and Diehl here http://www.iitk.ac.in/nicee/wcee/article/13_952.pdf?

Are you sure it's lambda40 that you plotted? Roughly, I can see 265 m/s at 9 Hz, hence about 30 m wavelength, not 40 m.

Well, it works more or less. Statistically, this is something that we observe. For a particular case, it can be completely correct or wrong. It's a bit like Vs30 deduced from the ground slopes. At a certain level of abstraction it works more or less, if you go into the details, then the physical model in this approach is far too simplistic. Without preaching for my own business (not expressed in dollars or euros), I'm convinced that the inversion step is mandatory to correctly understand the behavior of a particular site. DC curves are not always as clear as in the case you posted. A final correct interpretation have to be in agreement with all observables: MASW, H/V, downhole,... How do you check that your H/V curve is agreement with your Vs30 value?

Sorry !!! in the fig. Lambda is 29 m

thank you!!!!