Unlike Earth and the Moon, seismo-tectonic activity of Mars is poorly understood. While the origin of earthquakes in Earth is dominantly related to plate-tectonics, the seismicity of Mars is generally assumed to be related to global contraction due to planetary cooling as well as to local to regional lithospheric displacements related to magmatic activity, lithospheric loads, tides and impacts. An outstanding scientific question regarding Mars is whether it remains seismically active or not. If active, what parts of Mars are seismically active, and what are the geological structures involved in the seismic processes? Instrumental records of marsquakes do not exist. Therefore, NASA’s InSight mission will land on Elysium Planitia, install a seismometer package, and record Martian seismic activities (both marsquakes and meteoroid impacts) for the first time beginning December 2018. Knowledge of the spatial and temporal distribution of marsquakes provides important insights into geodynamic processes on Mars. Marsquakes can also be used to map Mars’ core, mantle and crust, as envisaged by the InSight mission. Since Mars lacks instrumental seismic records currently, present day seismicity of Mars has been estimated from geodynamic models and analysis of surface faults. These models suggest that Mars could be seismically active today. Among the many seismo-tectonically active sites considered, the Tharsis region is suggested to be a major centre of seismicity on Mars. However, published geologic constraints on such activity are sparse.
In this paper (Kumar et al., 2019), we used geomorphologic observations and crater size-frequency age determinations gleaned from high-resolution orbiter data to demonstrate that the Valles Marineris region (Figures 1 and 2) is recently seismo-tectonically active. The chasmata shows evidence of reactivated dip-slip faults that cross-cut the chasmata walls and floors and indicates up to 1-2 km total vertical displacement along the trough bounding faults. More than 16000 boulder fall occurrences with pristine trails are observed throughout the chasmata wall with an average slope of 25 degrees. The boulder falls are interpreted to have been triggered by recent seismic shaking from the shallow marsquakes occurring along the chasmata faults, possibly in the last thousands of years. Synthetic ground motion models indicate several MW 4-6 marsquakes at shallow depths (~1-6 km) are required to produce these canyon-wide boulder falls. In addition, the presence of many young landslides (22-790 Ma) proximal to the reactivated trough bounding faults and formation of thousands of possible mud volcanic cones throughout the chasmata floor all suggest marsquake-triggered shaking in the past tens to hundreds of million years, corresponding to Late to Middle Amazonian Epochs. We estimate formation of 20 m to 1.3 km diameter fresh impact craters around the chasmata had negligible contribution to the recent seismicity. Therefore, Valles Marineris tectonism is an important source of marsquakes that may be readily detectable by the upcoming InSight seismometers.
P. Senthil Kumar, N. Krishna, K.J.P. Lakshmi, S.T.G. Raghukanth, A. Dhabu and T. Platz (2019), Recent seismicity in Valles Marineris, Mars: Insights from young faults, landslides, boulder falls and possible mud volcanoes, Earth and Planetary Science Letters, 505, 1 January 2019, 51-64. https://doi.org/10.1016/j.epsl.2018.10.008
Figure :Surface features of CopratesChasma: (a) The interior of CopratesChasma exhibiting the landslides with IDs (OL = Ophir Labes and CL = Coprates Labes) and model formation ages labelled; different types of faults (see labels for symbology of fault types; continuous lines are certain, while dashed lines are approximate), the boulder falls exhibiting the trails (red clusters) and possible mud volcanoes (blue open circles) are also shown. The boxes are locations of Figures b and c; the background is MOLA topography superimposed on CTX imagery. (b) A portion of HiRISE image showing a pitted cone complex interpreted to be possible mud volcanoes. (c) The HiRISE image showing the boulder trails (red polylines); the dark patches are sand dunes; the inset Figure (d) illustrates a few boulder falls exhibiting trails with some containing boulders at their terminal ends.