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Abstract

Current seismicity of Mars is poorly known. Geodynamic models and analysis of surface faults indicate that Mars could be seismically active globally, particularly within the Tharsis region. However, published geologic constraints on such activity are sparse. In this study, we use geomorphologic observations and crater size–frequency age determinations gleaned from high-resolution orbiter data to demonstrate that the Valles Marineris region 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 M>sub>W>/sub>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.