The life span of fault-crossing channels

The offset of stream channels across a strike-slip fault offer a record of long-term slip rates. The process itself is an interesting case of landscape evolution because the streams will spill straight across the fault at some point and reset the offset. Dascher-Cousineau et al. developed a model for this process that they validated using observations from the Carrizo Plain in California. The model leverages transitions from active to abandoned stream channels to determine when and how drainage networks in these regions reorganize and allow quantification of both slip and bedload transport. Science , abf2320, this issue p. 204 A model for abandoned stream channels across a strike-slip fault provides a way to assess slip and landscape evolution. Successive earthquakes can drive landscape evolution. However, the mechanism and pace with which landscapes respond remain poorly understood. Offset channels in the Carrizo Plain, California, capture the fluvial response to lateral slip on the San Andreas Fault on millennial time scales. We developed and tested a model that quantifies competition between fault slip, which elongates channels, and aggradation, which causes channel infilling and, ultimately, abandonment. Validation of this model supports a transport-limited fluvial response and implies that measurements derived from present-day channel geometry are sufficient to quantify the rate of bedload transport relative to slip rate. Extension of the model identifies the threshold for which persistent change in transport capacity, obliquity in slip, or advected topography results in reorganization of the drainage network.