Figure 4. Subfigure A shows the right-lateral strike-slip Newport-Inglewood Fault Zone (NIFZ) in metropolitan Los Angeles, California, United States (34oN, 118oW). This is compared to strike-slip faults of Bathys Planum on account of: (1) morphological similarities between transpressional landforms; and (2) the intermittent occurrence of overstepping scarps in a regionally curvilinear trend on a plains-forming fill material. Transpressional features in stepovers and restraining bends along the fault are labeled. Digital elevation model (DEM) modified from publicly available files published by the United States Geological Survey (USGS_1_n34w199), and fault locations are modified from the USGS Q-faults database. Subfigure B shows a left-lateral strike-slip fault in Bathys Planum with similar stepover morphology.
When terrestrial strike-slip faults bend or step against their own sense (e.g., a left-lateral strike-slip fault either bends or steps to the right), a localized compressional stress is imposed within the bend or between the en echelon strands of that fault, creating a pop-up in the affected area. If a fault bends into its own sense (e.g., a left-lateral strike-slip fault either bends or steps to the left), a localized extensional stress is imposed in the fault’s bend or between its strands, creating a pull-apart basin [Aydin and Nur, 1985; Cunningham and Mann, 2007]. A fault may bend or step over in alternating directions, creating a “porpoising” effect where pull-apart basins and pop-ups may repeatedly alternate along the fault zone (Figure 4A; Sylvester, [1988]). Assuming these morphologies observed on Earth apply to faults in Bathys Planum, then the sense of observed faults can be inferred on the basis of the presence and distribution of these landforms. For instance, the faults mapped in Figure 3, show pop-ups at right steps, and small depressions at left steps, suggesting a left-lateral sense of slip along the faults. Note that the mound in the center-right of Figure 3 appears to be offset in a left-lateral sense by more than a kilometer, consistent with the inferred left-lateral slip along the faults from the morphology of steps and bends along the same fault zone. A terrestrial example of these morphologies is comparatively presented in Figure 4.
The “stair-stepping” deflection of the Claritas-radial graben in Figure 3 appears to be right-lateral rather than left-lateral in sense. This is interpreted not to be associated with the offset of later Claritas-radial graben. Rather, a pre-existing east-west fault system is inferred to have influenced the development of the Claritas-radial graben as the latter developed, creating an apparent right-lateral deflection in the graben as they propagated through Bathys Planum. The apparent right-lateral deflection of graben and cracks is also present where they intersect east-west faults that do not display strike-slip surface morphologies. The deflections are, however, generally consistent in strike with nearby east-west faults that do exhibit strike-slip landforms. The apparent deflections of graben in these locations could be the result of other strike-slip faults associated with this ancient east-west fault system, even if those east-west faults cannot be directly confirmed or mapped with available data.