TOPOGRAPHIC EXPRESSIONS OF LUNAR GRABEN

Graben, linear landforms with a down-dropped block of rock bounded by two opposing normal faults, have long been recognized on the Moon. Many of these structures have yet to be studied in depth using high-resolution spacecraft data to better assess their geomorphology. Normal faults were mapped across the lunar surface using the 100 meters-per-pixel Lunar Reconnaissance Orbiter Camera wide-angle camera global image mosaic. A total of 1750 individual fault segments were identified on the scale of the dataset. The majority of them occur at the periphery of the lunar maria with their orientations frequently in close alignment to the mare boundaries. Lunar Orbiter Laser Altimeter digital elevation models with a resolution of 512 ppd were used to assess the topographic expressions of the graben to study fault displacement profiles, displacement/length scaling relationships, and fault interactions. Fault lengths were measured from their map traces and displacements were derived from the structural relief of the graben, as there is no erosion on the Moon. We analyzed in detail 14 segmented graben, with a total of 161 individual faults. Displacement profiles were generated for these graben by measuring and plotting the displacements in ~5-km-intervals aligned with their respective positions along the lengths of the graben-bounding faults. Displacement profiles that incorporate both graben-bounding faults reveal maximum displacements and allow for a comparison of displacements between the two opposing faults. Their overall shapes are useful for understanding subsurface geology or fault interaction. Our findings indicate that faults range in length from 40 to 460 km and show maximum displacements from 133 to 2042 m, showing a large variability in fault geometry. Displacement profile shapes are typically peaked but may become plateaued due to fault linkage or restricted fault growth. Results reveal 15 peaked, 9 plateaued and 4 inconclusive profiles and highlight various interactions between faults. Interestingly, fault surfaces facing toward the mare show greater displacements than those facing away from them. Further fault analysis will help to better understand regional- and global-scale extensional tectonic processes on the Moon.