Flume experiments on the horizontal stream offset by strike‐slip faults

Flume experiments, in which the middle section of an erosion channel is displaced horizontally, have been conducted to assess the response of streams to horizontal displacement by a strike‐slip fault. The experimental erosion channel was developed in a mixture of sand and clay, which provided relatively stable banks with its cohesiveness. Horizontal displacement of a strike‐slip fault perpendicular to the channel is expected to add a at section to its longitudinal prole along the fault line. The experimental stream eliminated this at section with downstream degradation, upstream aggradation, and lateral channel shift. As a result, a roughly continuous longitudinal prole was maintained. This maintenance of a continuous longitudinal prole along channel is considered to be the principle of stream response to horizontal displacement by a strike‐slip fault. Downstream degradation was the dominant process of this stream response in the overall tendency of erosion without sand supply. When the rate of fault displacement was low (long recurrence interval), the experimental stream eroded the fault surface, jutting laterally into the channel like a scarp, and deected the channel within the recurrence interval. This lateral channel shift gave some gradient to the reach created by fault displacement (offset reach), and the downstream degradation occurred as much as completing the remaining longitudinal prole adjustment. When the rate of fault displacement was high (short recurrence interval), the lateral erosion on the rst fault surface was interrupted by the next fault displacement. The displacement was then added incrementally to the existing channel offset making channel shift by lateral erosion increasingly difcult. The channel offset with sharp bends persisted without much modication, and downstream degradation and upstream aggradation became evident with the effect of the offset channel course, which worked like a dam. In this case, a slight local convexity, which was incidentally formed by downstream degradation and upstream aggradation, tended to remain in the roughly continuous longitudinal prole, as long as the horizontal channel offset persisted. In either case, once the experimental stream obtained a roughly continuous gradient, further channel adjustment seemed to halt. Horizontal channel offset remained to a greater or lesser extent at the end of each run long after the last fault displacement. Copyright © 2004 John Wiley & Sons, Ltd.