Characterization of thrust faults on the moon using fault dynamics and three-dimensional visualizations

Jaclyn D Clark, University of Texas at El Paso


Many small, lobate scarps, interpreted to be the surface traces of thrust faults, have been found all over Earth's moon by previous researchers. Fault dynamical calculations, assuming an initially completely molten Moon, have shown that these scarps can form due to compressional stresses that accumulate over time as the result of large-scale contraction of the Moon as it cooled. With high-resolution images from the Lunar Reconnaissance Orbiter Camera (LROC), previously undetected lobate scarps can be found globally and viewed at high resolution. By investigating these fault scarps, we can determine better constraints on the amount of crustal shortening and improve our understanding of the stress state of the Moon. In addition, the lobate scarps allow us to further test between competing models for the initial thermal state of the Moon, i.e. whether it was initially completely molten or if the molten portion was limited to a global magma ocean. To address these issues, I conducted basic structural analyses of lobate scarps at two locations on the Moon. One location lies in the highly cratered highlands between the craters Apollo and Korolev near the South Pole Aitken Basin. The other location lies between Mare Imbrium and Mare Serentatis near the Apollo 15 landing site. Simple calculations using Mohr-Coulomb failure laws are used to constrain quantities such as fault dip, maximum depth of faulting, and the magnitude of compressive stresses. Input parameters for these calculations - including the radius of curvature of the scarps, fault trace length, and orientation - were directly measured from high-resolution LROC imagery. Using crater counting methods, the ages of the fault scarps at the study sites were also determined. The amount of shortening and the rate of slip on faults were then calculated from the modeled ages and geologic cross-sections. We find 41.2 m to 1.3 km of total horizontal throw across the lobate scarps we studied, and horizontal throw rates that range from 1.1 m/Ma to 93.3 m/Ma. The total vertical throw was found to be 15 m to 115 m, with total vertical throw rates of 0.6 m/Ma to 8.2 m/Ma. Total net slip was also calculated and ranges from 51.5 m to 1.3 km, with net slip rates of 1.3 m/Ma to 93.6 m/Ma. Because the lobate scarps we studied have crisp morphologies, young modeled ages, and high stress values, we favor the ITM thermal model for the Moon.

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Recommended Citation

Clark, Jaclyn D, "Characterization of thrust faults on the moon using fault dynamics and three-dimensional visualizations" (2012). ETD Collection for University of Texas, El Paso. AAI1512559.