Adding focal plane solid models
The combination of focal mechanism diagrams and depth data is intended to convey a full three-dimensional understanding of earthquake distributions. However, it is difficult for an observer to determine whether a particular nodal plane is shared by neighboring seismic events or whether a plane’s orientation is precisely parallel to an underlying map feature, for example. To aid visualization and analysis, solid models of nodal planes are here added to the beach balls (Figure 9).
Figure 9a. Nodal planes
Figure 9b. Nodal planes - alternate view
Figure 9c. Fault plane versus auxiliary plane
The planes are colored where they bound contractional first motions (T quadrants) and are white where adjacent to dilatational (P) quadrants of the associated beach balls. Default versions of the models are included in the download file with the file names such as NP_Black. dae, NP_Blue.dae, etc. Variants with small arrows marking fault slip directions are labeled NParo_Black.dae, NParo_Blue.dae, etc.
The example illustrated in Figure 9 represents two different focal mechanism solutions for the 2006 Kiholo Bay earthquake. The same approach could be taken to representing aftershocks and neighboring historic events. In Figure 10, multiple nodal planes for historic earthquakes in the Hawaiian eastern rift zone reveal the presence of a low angle décollement surface. Click here for a movie version of this image [Kiholo Bay movie]
Figure 10. Hawaiian historic data