| dc.description.abstract | The outer rise is a topographic bulge seaward of the trench at a subduction zone that is caused by bending and
flexure of the oceanic lithosphere as subduction commences. The classic model of the flexure of oceanic lithosphere
w(x) is a hydrostatic restoring force acting upon an elastic plate at the trench axis. The governing
parameters are elastic thickness Te, shear force V0, and bending moment M0. V0 and M0 are unknown variables
that are typically replaced by other quantities such as the height of the fore-bulge, wb, and the half-width of the
fore-bulge, (xb− xo). However, this method is difficult to implement with the presence of excessive topographic
noise around the bulge of the outer rise. Here, we present an alternative method to the classic model, in which
lithospheric flexure w(x) is a function of the flexure at the trench axis w0, the initial dip angle of subduction β0,
and the elastic thickness Te. In this investigation, we apply a sensitivity analysis to both methods in order to
determine the impact of the differing parameters on the solution, w(x). The parametric sensitivity analysis
suggests that stable solutions for the alternative approach requires relatively low β0 values (< 15°), which are
consistent with the initial dip angles observed in seismic velocity-depth models across convergent margins
worldwide. The predicted flexure for both methods are compared with observed bathymetric profiles across the
Izu-Mariana trench, where the old and cold Pacific plate is characterized by a pronounced outer rise bulge. The
alternative method is a more suitable approach, assuming that accurate geometric information at the trench axis
(i.e., w0 and β0) is available. | |
