Understanding displacement accumulation rates and timing of fault events is crucial to constrain models of fault growth and seismic risk in active settings. Previous studies have attempted to unravel fault growth histories in a qualitative sense, but the lack of a suitable dating technique for natural fault systems has limited the models' ability to predict rates and variations in rate, of displacement accumulation during development of a fault array. This work unites the traditional disciplines of structural geology, geomorphology and geochemistry in a quantitative analysis of extensional fault array evolution and drainage response to deformation. In particular, the study involves detailed mapping of fault systems and associated drainages, in tandem with Surface Exposure Dating using in-situ cosmogenic nuclides, to determine chronology and rates of fault growth during the complete cycle of fault growth from initial propagation to physical linkage.
The study area is located in the Canyonlands Graben of southeastern Utah, where extensional faulting has occurred in the last 0.5 m.y. and is ongoing. It is one of the finest areas for this type of investigation, as the faults are exceptionally well exposed in a variety of fault interaction orientations, drainage responses are readily observed, and the exposed lithology and time scale is very appropriate for Surface Exposure Dating.
The research involves careful physical mapping on aerial photographs and a 5-meter Digital Elevation Model, followed by more detailed field mapping of fault linkage zones and associated deformed drainage systems. Combined with an extensive Surface Exposure Dating study using in-situ Berylium-10, Aluminum-26 and Carbon-14 extracted from quartz-rich bedrock samples along stream beds and fault scarps, this approach yields unique quantitative information about the timing and rates of faulting. In addition, fluvial deformation will be correlated to specific events of displacement accumulation and will be used to evaluate the mechanisms and rates of fault-related knickpoint retreat through the landscape. The results of this research will provide, for the first time, a complete, quantitative reconstruction of fault growth rates through the entire cycle of lateral fault propagation, through interaction and linkage.
This, in turn, will significantly improve the understanding of the fundamental processes underlying fault array evolution and thus increase the reliability of seismic risk assessments and sedimentary basin analysis. The research will also have important implications for understanding erosion and mass sediment removal through bedrock channel erosion, which is considered a governing force in the tectonic evolution of mountainous terrains.
