Geomorphological traits of landscapes in continental rifts—From fault-elastic rebound to sedimentary sinks

Abstract

We analyse 498 faults identified in satellite imagery and interpret the height and width of associated footwall ranges with respect to co-seismic elastic rebound from tectonic and erosional unloading. The dynamics of footwall uplift link uplands to catchment patterns and interrelated hanging wall sedimentary fans. Height–length relations of some catchments and associated alluvial fans scale linearly whereas others, such as fault-slope catchments and related down-fault fans (building out from faults) show a significant scatter without an obvious trend. Perched basins abandoned in the footwalls of younger faults offer catchment-fan height–length relations like watergap and dipslope-related fans and, besides, hint at reduction of dip angle due to rollback of larger faults before abandonment. Analysis of the width-to-height ratio (W/h) of footwall ranges offer a robust linear statistical trend, h = 0.06 W and is identical between datasets. This trend is valid for both arid and tropical rifts, the latter offering smaller rebounds. Contributions of elastic rebound on fault throw in our data are simplistically considered through comparison to global trends on fault length versus throw. This allows consideration around maximum throw (T_max) linked to the maximum height of footwall ranges (h) and to their width (W) above the reference level. Basic calculations indicate that co-seismic rebound contributes from <1% to 17% of extensional fault throw. Width-to-height ratios for large faults (L > c. 50 km) show less spread than smaller faults. Such large faults expectedly dissect the brittle crust, indicating that these large faults which root in the ductile–brittle transition approach a balanced, steady-state kinematic pattern. We speculate that significant crustal thinning associated with these large faults triggers the onset of isostatic adjustments that drive fault rotation, instigating fault abandonment and disconnected perched basins.