RADAR AND PHOTOCLINOMETRIC STUDIES OF WRINKLE RIDGES ON MARS

Earth-based radar altimetry and image derived photoclinometric profile s were analyzed to examine both the long- and short-wavelength topogra phy associated with wrinkle ridges on Mars. Photoclinometrically deriv ed elevation data across wrinkle ridges were evaluated to determine th e sensitivity of profiles to two empirical photoclinometric parameters , the horizontal digital number (HDN) and the scattered light value (S LV). The photoclinometric profiles are extremely sensitive to small va riations in HDN. The sense of slope of a profile can be completely rev ersed over a range in HDN of as little as +/-1. Comparably small varia tions in the SLV have relatively minor effects on the photoclinometric ally derived elevations. The existence of elevation offsets from one s ide of the ridge to the other, reported in previous photoclinometric s tudies of martian wrinkles, were not confirmed through photoclinometry . In addition, no evidence of elevation offsets were found in Earth-ba sed radar altimetry profiles across wrinkle ridges. In order to more a ccurately model wrinkle ridge topography, we controlled photoclinometr ically derived elevations with long-wavelength topography obtained fro m the radar altimetry. The results of this study do not support kinema tic models for the origin of planetary wrinkle ridges that involve dee ply rooted thrust faults which separate crustal blocks at different el evations. A kinematic model involving buckling of shallow crustal laye rs into concentric folds that close, leading to the development of thr ust faults, is consistent with wrinkle ridge morphology and terrestria l analogs. Recent geophysical studies of terrestrial analogs and the i nfluence of shallow subsurface structures, particularly buried craters , on the localization of many wrinkle ridges on Mars suggest that thru st faults associated with the ridges are confined to the ridged plains material and do not extend into the lithosphere.