Variations in oceanic plate bending along the Mariana trench

Abstract

We quantify along-trench variations in plate flexural bending along the Mariana trench in the western Pacific Ocean. A 3-D interpreted flexural deformation surface of the subducting Pacific Plate was obtained by removing from the observed bathymetry the effects of sediment loading, isostatically-compensated topography based on gravity modeling, age-related lithospheric thermal subsidence, and residual short-wavelength features. We analyzed flexural bending of 75 across-trench profile sections and calculated five best-fitting tectonic and plate parameters that control the flexural bending. Results of analysis revealed significant along-trench variations: the trench relief varies from 0.9 to 5.7 km, trench-axis vertical loading (-V0) from -0.73 × 1012 to 3.17 × 1012 N/m, and axial bending moment (-M0) from 0.1 × 1017 to 2.7× 1017 N. The effective elastic plate thickness seaward of the outer-rise region (Te M) ranges from 45 to 52 km, while that trench-ward of the outer-rise (Te m) ranges from 19 to 40 km. This corresponds to a reduction in Te of 21-61%. The transition from Te M to Te m occurs at a breaking distance of 60-125 km from the trench axis, which is near the outer-rise and corresponds to the onset of observed pervasive normal faults. The Challenger Deep area is associated with the greatest trench relief and axial vertical loading, while areas with seamounts at the trench axis are often associated with more subtle trench relief, smaller axial vertical loading, and greater topographic bulge at the outer-rise.