Analysis of Unusual Fault Structures in Terra

Introduction: Most major geologic structures on Mars are related to a major volcanic province (Tharsis, Elysium) or a large impact basin. It is of interest then to identify and study tectonic features not attributable to known volcanic provinces or impact basins. Located in the central Terra Cimmeria region of the Southern Highlands of Mars is a set of linear scarps not clearly associated with major known tectonic provinces. Several scarps exhibit relief in excess of 500 meters and the set displays a consistent NE-SW trend for over 1500 kilometers. The analysis of these scarps of undefined origin is divided into three parts. The first element is mapping and characterization of the observable scarps. The next is construction of a geologic history aided by the determination of the relative age of the scarp set by use of crater counts and cross cutting relationships. The final point is to incorporate the formation of this scarp set into the account of Mars’ geological evolution. Methodology: Using data from Mars Global Surveyor (MGS) and imagery from the Viking missions, the scarps were mapped and characterized by recording data in tabular form. Attributes measured include relief, azimuth, dip direction, and length. The bounding coordinates of the study area are 35S to 70S and 100E to 170E. Topographic data from the Mars Orbiter Laser Altimeter (MOLA) was used at a resolution of 64 pixels/degree. A mosaic of Viking mission imagery was used at a resolution of 256 pixels/degree. To augment the Viking imagery, Mars Orbiter Camera (MOC) wide-angle images were also imported at a resolution of 256 pixels/degree. We conducted a crater count of the region to date the surface on which the scarps developed. Using Viking imagery spanning an area of 2.2x10 km in central Terra Cimmeria, the diameters (D) of 937 craters were recorded. The diameter values were placed in √2 bins ranging from 4 km to 256 km. An additional count was completed in Sabaea northwest of Hellas Planitia to date the scarp formation relative to the surface created by the ejection of material from the Hellas impact. Here the diameters of 585 craters were measured over an area of 7.8x10 km. Figure 3 shows an incremental size frequency distribution of both counts compared to isochrons from Hartmann[1]. To correlate scarp development with the Terra Cimmeria crater count, we assume that we can estimate the age of scarp formation as a percentage of the age of the cratered surface by discerning the percentage of unfaulted scarp-crossing craters. We first mapped all craters that cross scarps. Using topographic profiles and both MOC and Viking imagery we determined whether or not each crater was faulted. Through this examination we obtained a percentage value that yields the age of scarp development relative to the Terra Cimmeria crater count and thus relative to other features on Mars. Results: The mean strike of 159 measured features is N35E when azimuth values are graphed on a rose plot with 10 bins (Figure 1). The maximum observed