Fig. 1

Moment tensor eigenvalue space and basal projections. Graphical representation of the moment tensor eigenvalue space \(\left( {\lambda_{1} , \lambda_{2} , \lambda_{3} } \right)\). The blue line corresponds to the condition \(\lambda_{1} = \lambda_{2}\), and the red line corresponds to the condition \(\lambda_{2} = \lambda_{3}\). The green region represents the condition \(\lambda_{1} \ge \lambda_{2} \ge \lambda_{3}\). Locations of DC, ±CLVD, and ±ISO source types on the surface are shown by their corresponding beach-ball symbols. a In the basal cubic projection, all mechanisms are projected onto two triangles on the cube defined by \(\hbox{max} \left( {\left| {\lambda_{1} } \right|, \left| {\lambda_{2} } \right|, \left| {\lambda_{3} } \right|} \right) = 1\). The subgrid interval is 0.5. b In the basal hexagonal bi-pyramid projection, all mechanisms are projected onto four triangles on the hexagonal bi-pyramid that fits the cube of a, which is shown in gray. c In the basal conjugate hexagonal bi-pyramid projection, all mechanisms are projected onto the two triangles on the hexagonal bi-pyramid. The hexagonal bi-pyramid of b is shown in gray. d In the basal spherical projection, all mechanisms are projected onto a lune on the sphere