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

Zhang Fan; Lin Jian; Zhou Zhiyuan

doi:10.1007/s13131-019-1493-4

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Article Navigation > Acta Oceanologica Sinica > 2019 > 38(11): 81-90

Zhang Fan, Lin Jian, Zhou Zhiyuan. Intra-trench variations in flexural bending of the subducting Pacific Plate along the Tonga-Kermadec Trench[J]. Acta Oceanologica Sinica, 2019, 38(11): 81-90. doi: 10.1007/s13131-019-1493-4

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Zhang Fan, Lin Jian, Zhou Zhiyuan. Intra-trench variations in flexural bending of the subducting Pacific Plate along the Tonga-Kermadec Trench[J]. Acta Oceanologica Sinica, 2019, 38(11): 81-90. doi: 10.1007/s13131-019-1493-4

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

doi: 10.1007/s13131-019-1493-4

1.
Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;Innovation Academy of South China Sea Ecology and Environmental Engineering, Chinese Academy of Sciences, Guangzhou 510301, China
2.
Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA;Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China

Received Date: 2018-04-26

Abstract

Abstract

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_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 (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_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 T_e reduction of 28%–36% and average T_e reduction area S_{△T_e} 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_e^M and T_e^m both in general increase with the subducting plate age.
- Tonga-Kermadec Trench|horizon deep|axial vertical force|axial bending moment|effective elastic thickness|flexural curvature analysis,

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