Adjust Seattle fault representation and weights

[pmpowers-usgs]

The Seattle fault should be modeled similar to how the Southern Whidbey Island fault is modeled. The geodetic models should only include the 'dominant' strand. For 2014 the, geologic model/rates were simply copied to the geodetic models so any modeled slip rates were not used. Moreover, some very low rate (1e-7) characteristic/unsegmented branches were added for the middle and southern strands, whereas only the northern strand is required for consistency with the 2008 unsegmented model.

[pmpowers-usgs]

The middle and southern strands have been removed from Zeng and Bird and the rates for their northern strand updated based on their computed slip rates and a fixed mag of 7.23 from the geologic model northern strand ( bf13c12 ).

There is still an open issue as to why the characteristic geologic middle and southern strands are assigned very low rates but the rates are the same in the GR model (punting to 2017).