Morphometric Characterization of Longitudinal Striae on Martian Landslides and Impact Ejecta Blankets and Implications for the Formation Mechanism

摘要

Longitudinal striae are a shared characteristic of long run-out landslides and layered ejecta crater deposits. They appear to be a fundamental feature of disintegrated mass flows, but their formation and the required conditions are poorly understood. We evaluated their similarity using spectral analysis and assessed the possibility of a common formation mechanism. The topography of striae is scale-invariant in the form of a power law relationship of the power spectrum and the derived spectral exponent and amplitude factor, which are a measure for roughness, show similar correlations on both types of deposit. There is no correlation to geologic substrate units, latitude, or age. Parameter values are isotropic in horizontal direction for ejecta deposits and show a weak anisotropy for landslide deposits. Spectral parameter values of substrate topography match well with the values of the superposed deposit, which indicates that roughness is transferred from substrate to deposit surface during emplacement. Testing different geometric models, we find that a simple superposition of topography with a semideterministic, anisotropic pattern does not reproduce the patterns of our data. We find that phase locking of a surface with scale-invariant properties creates striae with fractal properties close to our natural data sets as well as recreating other morphological features that can form alongside striae. Although the transferal of substrate roughness cannot be fully conciliated with conventional flow models, we find that a model that combines advection with lateral diffusion accounts for the unidirectional preservation of phase information and is also consistent with the scale-invariance of striae. Plain Language Summary Longitudinal striae are a prominent surface feature of many types of mass movements, for example, long run-out landslides on Mars and Earth and layered ejecta crater deposits. It is unclear how they form or whether they form by the same process on the different types of deposits. Using high-resolution remote-sensing data of pristine Martian landslides and layered ejecta craters, we find that the similar appearance of striae can be confirmed by shared morphometric properties. Fourier methods reveal a scale-invariant topography where the roughness of longitudinal and perpendicular profiles is surprisingly similar. It is even similar to the roughness of the topography outside the striated regions, so that it may be inherited from the underlying substrate. This weak anisotropy in roughness cannot be responsible for the distinct pattern of striae. The latter is probably related to the phases of the Fourier components rather than to the amplitudes that are responsible for the roughness. These characteristics include scale-invariance, weakly anisotropic fractal properties and a roughness that appears to be transferred from the substrate. Testing of formation models shows that a formation process that conserves phase information of topography is most consistent with our data. We suggest that a flow process that combines advection with lateral diffusion of topography can enable phase locking and is also consistent with the fractal properties of striae.