Gradients in extension and strain at Valles Marineris, Mars

Extension and strain are calculated for six profiles across the Valles Marineris troughs. Extension accommodated by the large trough normal faults varies systematically along the length of the trough system, increasing from 5 to 10 km near the eastern and western termini to a maximum value of 20–30 km near the center, assuming 60° fault dip angles and ±1 km in trough relief. The spatial gradient in extension exceeds reasonable uncertainties in both topography and fault dip, demonstrating an inhomogeneous deformation field along strike, similar to other well documented examples of normal faults and grabens on Earth. Strain also varies with position, typically between 5 and 20%. Smaller values of strain reported for the Valles Marineris region, <2%, that include large expanses of unextended terrain represent spatial averages that may underestimate the magnitude of strain at the troughs.