Segregate sources and supply inline comments for exceptions

[pmpowers-usgs]

Migrated from usgs/nshm-cous-2014#16

The 2014 update saw the unification of WUS sources in input files based on their being geologic or geodetic. This created much confusion with respect to GR/CH weight ratios, which vary by region (50/50 or 33/67). It also didn't solve the problem of having the same fault defined in multiple files (GR vs CH).

The preferred approach would be to have single files per (and named by) region or state (reverting to 2008 practice) wherein a fault source is defined once and all associated MFD's are listed together. This would provide a complete picture of any particular fault in a single place. Additional MFD attributes would be used to identify the source of the slip rate used to derive rupture rates.

Any exceptional faults would also be carved out into their own file with inline explanations of how their numbers were derived. For example, there might be independent files for all fixed magnitude faults (e.g. Seattle, Dixie Valley), faults designated as having a probability of occurrence <1.0 (PNW offshore faults), and faults with alternate slip rate branches (e.g. Saddle Mtn.; for 2014 this would have 8 MFDs: 2 Bird, 2 Zeng, and 4 geologic).