Science report 02/19/2013
The site of MDRS has not been exposed to much tectonic force, one must think initially. All the layers are consequently dipping to the west at less than 10 degrees. Not much variation except for some channel fillings and big cross bedded sedimentary structures. But even this minimal dipping of strata must be caused by a tectonic force. A small isostatic bounce somewhere, a gently subsiding basin, some force offsetting the area we are walking on. But if we zoom out we see that there must have been some big forces in this area that put stress on the subsurface. Mt. Ellen is the high rising reminder of that if one looks to the south. There must be some relics of those forces torturing this area and if one looks closely, small faults and cracks are scars of an old battle that once roamed in the subsurface.
Analyzing satellite data is a valuable source for collecting interesting sites and regions regarding the history of the landscape surrounding MDRS. Zooming in on the Lith canyon, which is located less than two kilometers to the east of MDRS, the serrated edges are very noticeable. But in a northeastern branch of this of this water carved feature a straight line appears, located from UTM: 12S 521350 4251887 to 12S522084 4251339. This is a fault with a strike orientated from 125 to 305degrees, this is perfectly in line withe the dominant joint fracture patterns that have been measured earlier. Those have exactly the same direction.
At the northern part the fault is clearly visible in the soft strata, here layers of clay, sand and gypsum are doubled in sequence, torn and nearly vertically positioned. The surface has some deep canyons, eroded by water, in line with the fault and the preference of draining to have the path of least resistance.
The soft and weather beaten sediments surrounding this fault, like clays, gypsum and sandstone are not the best capturers for fault patterns and stress related features. But at 12s521616 4251697 the well sorted, angular and well cemented white sandstones had several fractures in several directions. Measured fractures that coincide with the big fault are 024/80, 030/84 and 034/76 and are with respect to the deviations good in similarities. The other fractures are orientated in 225/80, 224/90, 230/60 and 220/90 and also have a small deviation. Spacing between fractures with similar direction is roughly 15 to 50 centimeters.
Approximately 230 meters to southeast, at location 12s 521802 4251571 measurements were taken, giving orientations of 210/78, 230/74, 196/82 and 022/86. Of course much more measurement would be required to give a plausible explanation; also a sense of movement would be highly recommended to give a plausible explanation. But theoretically, if this fault would be strike slip with a compressional component, the fractures orientated around 220/80 could very well be the R' shears and the 030/90 orientated fractures the riedel shear component of the dominant S1 stress. The big fault would then be a result of the dominant riedel shears.
I'm am going to look further into this and will try to make as good a structural analysis as possible with the little data there is.
Regards,
Dennis Oltheten