To address the question posed earlier of whether the combination of various stress regimes is a legitimate logical step, I have prepared the below figure illustrating a confluence of stress directions that intersect in a region. These ideas are in Figure 4. Careful study of caption and cartoon should clarify the concept. By thus considering the Sh azimuth on the normal faulting regime, I believe it is plausible to map using all faulting regime data as input.
As to the meaning of the concentrations of force shown in the maps, there are three interpretations that seem plausible. The first, and least exciting, is that these patterns are merely a function of the uneven distribution of data. This is suggested distinctly by the thrust regime data from the Pacific plate map, and is the reason why all maps are produced with the data points used in their calculation are included on the one of the outputs. I beleive investigation of this interpretation could be made by making smaller area maps utilizing small subsets of the data.
The physical explanations that are left I refer to as the Force or Focus question and are the final two options I have considered. Basal drag on mountain roots in continental crust by mantle convection could be a source of intraplate stress fields. The concentration of stress azimuth intersections shown by the maps could indicate the location of crustal deformation due to such local accelaration. Alternatively, the focus idea would be related to a ridge-push argument for intraplate stress fields. If an arcuate force source applies force evenly along its length, then it is easy to imagine a focusing of force as if a parabolic reflector of EM energy. In this scenario, the locations highlighted by the stress maps could indicate sites of potential secondary geologic phenomena such as volcanism, compression, or even tight interlocked stability.
("Pink" fault planes have turned light gray through the
file conversion process)