Abstract
Oceanic plates experience extensive normal faulting as they bend and
subduct, enabling fracturing of the crust and upper mantle. Debate
remains about the relative importance of pre-existing faults, plate
curvature and other factors in controlling the extent and style of
bending-related faulting. The subduction zone off the Alaska Peninsula
is an ideal place to investigate controls on bending-related faulting as
the orientation of abyssal-hill fabric with respect to the trench and
plate curvature vary along the margin. Here we characterize bending
faulting between longitudes 161°W and 155ºW using newly collected
multibeam bathymetry data. We also use a compilation of seismic
reflection data to constrain patterns of sediment thickness on the
incoming plate. Although sediment thickness increases by over 1 km from
156°W to 160°W, most sediments were deposited prior to the onset of
bending faulting and thus have limited impact on the expression of
bend-related fault strikes and throws in bathymetry data. Where magnetic
anomalies trend subparallel to the trench (<30°) west of
~156ºW, bending faulting parallels magnetic anomalies,
implying bending faulting reactivates pre-existing structures. Where
magnetic anomalies are highly oblique (>30°) to the trench
east of 156ºW, no bending faulting is observed. Summed fault throws
increase to the west, including where pre-existing structure
orientations do not vary between 157-161ºW, suggesting that the increase
in slab curvature directly influences fault throws. However, the
westward increase in summed fault throws is more abrupt than expected
for changes in slab bending alone, suggesting potential feedbacks
between pre-existing structures, slab dip, and faulting.