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Abstract

We attribute changes in the morphology of relay ramp channels (increased slope and decreased width) to variations in displacement rate on ramp-adjacent normal faults. We map the faults and fluvial channels associated with four sites in different stages of fault interaction and linkage on the Volcanic Tableland, a Late Pleistocene ash-flow tuff in east-central California. Because these channels are inactive today, we estimate downstream changes in channel width and depth using HEC-RAS, a one-dimensional open channel flow model. Our results show that channel slope must be greater than about 0.05 before there are substantial decreases in width or substantial increases in depth. Displacement rate increases during interaction between en echelon segments results in the increases in channel slope and decreases in channel width. Moreover, our data show that these changes begin to occur during the very early stages of fault interaction, well before the fault geometry would indicate ongoing or imminent linkage.