Intra- and intertrench variations in flexural bending of the Manila, Mariana and global trenches: implications on plate weakening in controlling trench dynamics

Abstract

S U M M A R YWe conducted detailed analyses of a global array of trenches, revealing systematic intra-and intertrench variations in plate bending characteristics. The intratrench variations of the Manila and Mariana Trenches were analysed in detail as end-member cases of the relatively young (16-36 Ma) and old (140-160 Ma) subducting plates, respectively. Meanwhile, the intertrench variability was investigated for a global array of additional trenches including the Philippine, Kuril, Japan, Izu-Bonin, Aleutian, Tonga-Kermadec, Middle America, Peru, Chile, Sumatra and Java Trenches. Results of the analysis show that the trench relief (W 0 ) and width (X 0 ) of all systems are controlled primarily by the faulting-reduced elastic thickness near the trench axis (T m e ) and affected only slightly by the initial unfaulted thickness (T M e ) of the incoming plate. The reduction in T e has caused significant deepening and narrowing of trench valleys. For the cases of relatively young or old plates, the plate age could be a dominant factor in controlling the trench bending shape, regardless the variations in axial loadings. Our calculations also show that the axial loading and stresses of old subducting plates can vary significantly along the trench axis. In contrast, the young subducting plates show much smaller values and variations in axial loading and stresses.

Flexural Analysis Along the Sunda Trench: Bending, Buckling and Plate Coupling

“…Highest T ES estimates are found for sections 3, 9, and 20, 21, and 22. The reduction in elastic thickness from seaward of profile to trenchward for each section is found to be varying significantly along the trench with up to 60% reduction at section 9 and a significant reduction of around 50% at most regions along the trench similar to the values observed by Zhang et al () and almost no reduction at section 16 (Figure d). The distance at which the change in elastic thickness happens along the profile, which is associated with predominant normal faulting along the profile is found to be ~40–70 km all along the trench.…”

Deep Seismic Structure Across the Southernmost Mariana Trench: Implications for Arc Rifting and Plate Hydration

“…The convergence between the Pacific and Philippine Sea plates is approximately orthogonal to the E‐W trench in the southernmost Mariana margin, which differs significantly from the mostly N‐S trend of the IBM arc (Figure ; Bird, ). In the southernmost Mariana, the trench reaches the deepest point on Earth at the Challenger Deep, which is subjected to the greatest tectonic loading and bending (Zhang et al, , ). This region lacks a well‐defined arc and is characterized by spatially distributed forearc segments that are separated from the Mariana forearc farther north (Figure ; Martinez et al, ; Ribeiro et al, ).…”

Outer trench slope flexure and faulting at Pacific basin subduction zones

“…Our analysis is similar to the global compilation by Levitt & Sandwell (1995) and later work by Bry & White (2007) but with a few significant differences, foremost of which is that those studies used constant-rigidity thin plate flexure to model gravity and topography profiles. Meanwhile, recent efforts that attempted to improve upon them by developing methods for variable-rigidity plates instead (Hunter & Watts 2016;Zhang et al 2017) are more closely related to our study, however, we will also mention some important distinctions in the details further below. The Levitt & Sandwell (1995) study limited the bathymetry to actual soundings while the Bry & White (2007) used actual soundings averaged over 710 E.S.M.…”

“…This is in contrast to some previous approaches in which the variable elastic thickness of a plate is represented with discontinuous regions of constant thickness, or a 'stair-step' form. Such stair-step variations in elastic thickness have been applied to modelling of trench-perpendicular profiles of bathymetry along the Chile (Contreras-Reyes & Osses 2010) and Mariana (Zhang et al 2014) subduction zones, as well as for a selection of subduction zones globally (Zhang et al 2017). In another study comparing the strength of the incoming plate across multiple trenches, ensemble average profiles of marine gravity anomalies within regions of and across entire circum-Pacific subduction zones were used as inputs for inverse modelling to obtain models of ramplike variations of elastic thickness (Hunter & Watts 2016).…”