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.