STREAM CHANNEL OFFSETS ALONG STRIKE-SLIP FAULTS: EFFECTS OF FAULTING AND SURFICIAL PROCESSES

Stream channel offset is widely used as a geomorphic marker for identifying strike-slip faults and estimating geological fault slip rates. However, not all offsetting is caused by fault slip; surficial processes can also modify stream channels. We have simulated morphological evolution of stream channels affected by both strike-slip faulting and surficial processes using the finite volume method. Our results show that fault slip tends to offset stream channels, while surficial processes, mainly incision, tends to straighten them. Large and infrequent fault slip causes large offsets of stream channels, but the long-term slip rates based on stream channel offsets are usually smaller than the true values because of the competing effects of incision. In the extreme cases when fault creeps continuously and incision is relatively strong, no significant offsetting of stream channels are produced. We systematically examined the effects of tectonic and surficial factors including average slip rate, recurrence intervals of fault slip, incision rate, and the initial spacing of stream channels. We found that surficial processes usually reduce the apparent offsets of stream channels, causing underestimation of fault slip rates. However, river capturing could drastically change stream channel evolution, increasing the apparent stream channel offsets or even give a false sense of relative fault motion. Theses results call for careful studies of surficial processes when using stream channel offsets to estimate geological slip rates of strike-slip faults.