STREAM PROFILE ANALYSIS ALONG THE SOUTHERN SIERRA NEVADA FRONTAL FAULT ZONE

The mechanical linkage of normal faults can result in spatial and temporal variations in fault displacement. In this study we use ArcGIS^®, Matlab^®, and software from geomorphtools.org to perform stream profile analysis along the southern Sierra Nevada frontal fault zone (SNFFZ). This work aims to constrain the pattern of rock uplift and identify potential relay zone structures associated with fault evolution. Stream profile analysis is appropriate for this study since for both transport- and detachment-limited erosion, rock uplift rate is the primary control on the power law scaling relation between gradient and drainage area. For this study we expect to find higher channel steepness indices and rates of rock uplift where the processes of mechanical fault linkage have occurred most recently. Using mosaicked 10m digital elevation models from the USGS, watershed boundaries and longitudinal stream profiles were extracted for divide reaching drainages along the footwall of the SNFFZ. The relationship between channel slope and contributing drainage area for each watershed was then used to determine an average channel concavity and specify a regional reference concavity value. This information was used to calculate normalized steepness index values within each divide-reaching watershed. Preliminary findings, using an initial θ_ref = 0.45, indicate that the maximun channel steepness occurs around Cottonwood Creek, which drains much of the relay zone, with k_sn values decreasing in both directions along strike. Another trend evident in our early findings is a prominent knickpoint and change in channel morphology present in channel profiles of watersheds surrounding the Cottonwood Creek area. These channel profiles demonstrate below average concavity values at high elevations, and above average concavity values at lower elevations. Further work will characterize catchments both north and south of the left step in the range front marking the location of the Cottonwood Creek catchment system. This research holds the potential to provide insights regarding the tectonic evolution of the southern Sierra Nevada, the processes of normal fault interaction and linkage, and the seismic hazards associated with such processes.