Analysis of a new geomorphological inventory of landslides in Valles Marineris, Mars

We completed a systematic mapping of landslides in a 10(5) km(2) area in Tithonium and lus Chasmata, Valles Marineris, Mars, where landslides are abundant. Using visual interpretation of medium to high-resolution optical images, we mapped and classified the geometry of 219 mass wasting features, including rock slides, complex/compound failures, rock avalanches, debris flows, and rock glacier-like features, for a total landslide area of A(LT) = 4.4 x 10(4) km(2), 44% of the study area, a proportion larger than previously recognised. Studying the landslide inventory, we showed that the probability density of landslide area p(A(L)) follows a power law, with a scaling exponent alpha = -1.35 +/- 0.01, significantly different from the exponents found for terrestrial landslides,alpha = -2.2 and alpha = -2.4. This indicates that the proportion of large landslides (A(L) > 10(7) m(2)) is larger on Mars than on Earth. We estimated the volume (V-L) of a subset of 49 deep-seated slides in our study area and found that the probability density of landslide volume p(V-L) obeys a power law trend typical of terrestrial rock falls and rock slides, with a slope beta = -1.03 +/- 0.01. From the combined analysis of landslide area and volume measurements, we obtained a power law dependency comparable to a similar relationship obtained for terrestrial bedrock landslides, V-L = (1.2 +/- 0.8) x A(L)((1.25 +/- 0.03)) . From the fall height H-L and run out length L-L of a subset of 83 slides unaffected by topographic confinement, we obtained the mobility index (Helm's ratio) HULL, a measure of the apparent friction angle of the failed materials, phi = 14.4 degrees +/- 0.4 degrees. Slope stability simulations and back analyses performed adopting a Limit Equilibrium Method, and using Monte Carlo approaches on failed and stable slopes, suggest that the large landslides in Valles Marineris were seismically induced.