Incorrect mapping of Peter Bird zones to a-grid file

[pmpowers-usgs]

Reported by @AHajiSoltani and @JMAltekruse
Also noted by @treyapel and @nileshshome

WUS_zones_PB.in specifies:

0       !use hazgridXnga4. with wtgrid for M>6.5 Nov 14 2007
24.6 50. 0.05     EXTmapC.in for NGA firm rock Agrids new Sept 20 2007
-125. -100. 0.05
760. 2.
2 1. 0.0 1.0 5. 1.0 0.0  !2 depths
0.0 0.0 1.0 !weights to ss rev normal respectively
1. 300.
24.6 50. 0.1     !EXTENDED source grid 
-125. -100. 0.1
0.8 6.5 7.5 .1 3.
1 0 0 0
../conf/WUS/gridded/GR_DOS/agrd_zonesPB.out

agrd_zonesPB.out is a larger file (1MB) indicating it is a 0.05 degree discretized a-grid, but it is parsed as a 0.1 degree discretized grid. This grid source is used to represent diffuse faulting and is combined with other Peter Bird fault sources assuming a 0.05 degree calculation grid. There is a smaller 0.1 degree a-grid file in the GR_DOS directory that was probably being used at one point; when the larger, high-resolution file was adopted instead, this input file was not updated. The net result is these sources are not occurring where they should be. See attached image.

[pmpowers-usgs]

For consistency with fault sources (the hazard for which is computed at 0.05°), we:

• Keep conf/WUS/gridded/GR_DOS/agrd_zonesPB.out (0.1°)
• Delete conf/WUS/gridded/GR_DOS/agrd_bird_zones.out (0.05°)
• Update conf/WUS/gridded/WUS_zones_PB.in source grid spec to 0.05° discretization

[pmpowers-usgs]

It turns out that once both the 0.1° and 0.05° are correctly specified in WUS_zones_PB.in, a third zone, corresponding to the Hite Fault in SW Washington is also included. This is at odds with Figure 53 in the OFR. The Hite Fault is represented in all fault files; need to confirm (@haller-usgs) that the faults are reflecting the full slip rate and then can zero out a-grids.

[pmpowers-usgs]

closed by #24