TY  - JOUR
A1  - Regalla, Christine
A1  - Kirby, Eric
A1  - Fisher, Donald
A1  - Bierman, Paul R.
T1  - Active forearc shortening in Tohoku, Japan - constraints on fault geometry from erosion rates and fluvial longitudinal profiles
JF  - Geomorphology : an international journal on pure and applied geomorphology
N2  - Convexities in the longitudinal profiles of actively incising rivers are typically considered to represent the morphologic signal of a transient response to external perturbations in tectonic or climatic forcing. Distinguishing such knickzones from those that may be anchored to the channel network by spatial variations in rock uplift, however, can be challenging. Here, we combine stream profile analysis, Be-10 watershed-averaged erosion rates, and numerical modeling of stream profile evolution to evaluate whether knickzones in the Abukuma massif of northeast Japan represent a temporal or spatial change in rock uplift rate in relation to forearc shortening. Knickzones in channels that drain the eastern flank of the Abukuma massif are characterized by breaks in slope-area scaling and separate low-gradient, alluvial upper-channel segments from high-gradient, deeply-incised lower channel segments. Average erosion rates inferred from Be-10 concentrations in modern sediment below knickzones exceed erosion rates above knickzones by 20-50%. Although profile convexities could be interpreted as a transient response to an increase in rock uplift rate associated with slip on the range-bounding fault, geologic constraints on the initiation of fault slip and the magnitude of displacement cannot be reconciled with a recent, spatially uniform increase in slip rate. Rather, we find that knickzone position, stream profile gradients, and basin averaged erosion rates are best explained by a relatively abrupt spatial increase in uplift rate localized above a flat-ramp transition in the fault system. These analyses highlight the importance of considering spatially non-uniform uplift in the interpretation of stream profile evolution and demonstrate that the adjustment of river profiles to fault displacement can provide constraints on fault geometry in actively eroding landscapes. (C) 2013 Elsevier B.V. All rights reserved.
KW  - Knickzones
KW  - Fluvial longitudinal profile
KW  - Cosmogenic Be-10 erosion rates
KW  - Basement-involved thrusts
KW  - Futaba fault
KW  - Fukushima Prefecture
Y1  - 2013
U6  - https://doi.org/10.1016/j.geomorph.2013.04.029
SN  - 0169-555X
VL  - 195
IS  - 8
SP  - 84
EP  - 98
PB  - Elsevier
CY  - Amsterdam
ER  -