汤加-克马德克海沟俯冲板块挠曲变形与板块弱化

We conducted a detailed analysis of along-trench variations in the flexural bending of the subducting Pacific Plate at the Tonga-Kermadec Trench. Inversions were conducted to obtain best-fitting solutions of trench-axis loadings and variations in the effective elastic plate thickness for the analyzed flexural bending profiles. Results of the analyses revealed significant along-trench variations in plate flexural bending: the trench relief(W_0) of 1.9 to 5.1 km;trench-axis vertical loading(V_0) of –0.5×(10)~(12) to 2.2×(10)~(12) N/m; axial bending moment(M_0) of 0.1×(10)~(17) to 2.2×(10)~(17) N;effective elastic plate thickness seaward of the outer-rise region(T_e~M) of 20 to 65 km, trench-ward of the outer-rise(T_e~m) of 11 to 33 km, and the transition distance(X_r) of 20 to 95 km. The Horizon Deep, the second greatest trench depth in the world, has the greatest trench relief(W_0 of 5.1 km) and trench-axis loading(V_0 of 2.2×(10)~(12) N/m); these values are only slightly smaller than that of the Challenger Deep(W_0 of 5.7 km and V_0 of 2.9×(10)~(12) N/m) and similar to that of the Sirena Deep(W_0 of 5.2 km and V_0 of 2.0×(10)~(12) N/m) of the Mariana Trench,suggesting that these deeps are linked to great flexural bending of the subducting plates. Analyses using three independent methods, i.e., the T_e~M/T_e~m inversion, the flexural curvature/yield strength envelope analysis, and the elasto-plastic bending model with normal faults, all yielded similar average Te reduction of 28%–36% and average Te reduction area S￠Te of 1 195–1 402 km~2 near the trench axis. The calculated brittle yield zone depth from the flexural curvature/yield strength envelope analysis is also consistent with the distribution of the observed normal faulting earthquakes. Comparisons of the Manila, Philippine, Tonga-Kermadec, Japan, and Mariana Trenches revealed that the average values of T_e~M and T_e~m both in general increase with the subducting plate age.

Intra-trench variations in flexural bending of the subducting Pacific Plate along the Tonga-Kermadec Trench

We conducted a detailed analysis of along-trench variations in the flexural bending of the subducting Pacific Plate at the Tonga-Kermadec Trench. Inversions were conducted to obtain best-fitting solutions of trench-axis loadings and variations in the effective elastic plate thickness for the analyzed flexural bending profiles. Results of the analyses revealed significant along-trench variations in plate flexural bending: the trench relief (W₀) of 1.9 to 5.1 km; trench-axis vertical loading (V₀) of –0.5×1012 to 2.2×1012 N/m; axial bending moment (M₀) of 0.1×1017 to 2.2×1017 N; effective elastic plate thickness seaward of the outer-rise region (T_eM) of 20 to 65 km, trench-ward of the outer-rise (T_em) of 11 to 33 km, and the transition distance (X_r) of 20 to 95 km. The Horizon Deep, the second greatest trench depth in the world, has the greatest trench relief (W₀ of 5.1 km) and trench-axis loading (V₀ of 2.2×1012 N/m); these values are only slightly smaller than that of the Challenger Deep (W₀ of 5.7 km and V₀ of 2.9×1012 N/m) and similar to that of the Sirena Deep (W₀ of 5.2 km and V₀ of 2.0×1012 N/m) of the Mariana Trench, suggesting that these deeps are linked to great flexural bending of the subducting plates. Analyses using three independent methods, i.e., the T_eM/T_em inversion, the flexural curvature/yield strength envelope analysis, and the elasto-plastic bending model with normal faults, all yielded similar average T_e reduction of 28%–36% and average T_e reduction area S_△Te of 1 195–1 402 km2 near the trench axis. The calculated brittle yield zone depth from the flexural curvature/yield strength envelope analysis is also consistent with the distribution of the observed normal faulting earthquakes. Comparisons of the Manila, Philippine, Tonga-Kermadec, Japan, and Mariana Trenches revealed that the average values of T_eM and T_em both in general increase with the subducting plate age.