Graben, defined as landforms produced by normal faulting, have long been recognized on the Moon, but their map patterns, as well as topographic expressions, have not been studied systematically. The topography across graben and its along-strike variations reveal details about the growth of the normal faults forming the graben. Individual normal faults grow in length by the propagation of fault tips during slip events, which can also enlarge the displacement along the fault plane. Displacement and length accumulate and grow larger over time with more slip events, fault interaction, and linkage. We measured fault lengths and vertical offsets and then calculated the displacement for lunar graben using data from the camera and laser altimeter onboard the Lunar Reconnaissance Orbiter. Our study systematically investigated 14 graben systems across the lunar surface. Graben lengths were found to range from ∼43 to 453 km, and displacements ranged from ∼127 to 1115 m. These displacements were plotted against graben fault length to produce slip distributions, which revealed growth patterns involving mechanical interaction and fault linkage. Displacement-to-length scaling was used to further study the evolution of graben-bounding normal faults. We observed a sublinear growth pattern for lunar graben-bounding normal faults, consistent with growth of faults via segment linkage, where different stages of linkage are present on the lunar surface. Lunar graben-bounding faults show higher scaling ratios than previously estimated, likely due to variations in host-rock properties and mechanical stratigraphy.
Research Article|January 31, 2019
Topographic expressions of lunar graben
Melanie B. Callihan