Modeling of normal faulting in the subducting plates of the Tonga, Japan, Izu-Bonin and Mariana Trenches: implications f
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Modeling of normal faulting in the subducting plates of the Tonga, Japan, Izu-Bonin and Mariana Trenches: implications for near-trench plate weakening ZHOU Zhiyuan1, LIN Jian2, 1*, ZHANG Fan3 1 Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of
Sciences, Guangzhou 510301, China 2 Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543,
USA 3 Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen 518055,
China Received 29 March 2018; accepted 26 April 2018 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
The plate flexure and normal faulting characteristics along the Tonga, Japan, Izu-Bonin and Mariana Trenches are investigated by combining observations and modeling of elastoplastic deformation of the subducting plate. The observed average trench relief is found to be the smallest at the Japan Trench (3 km) and the largest at the Mariana Trench (4.9 km), and the average fault throw is the smallest at the Japan Trench (113 m) and the largest at the Tonga Trench (284 m). A subducting plate is modeled to bend and generate normal faults subjected to three types of tectonic loading at the trench axis: vertical loading, bending moment, and horizontal tensional force. It is inverted for the solutions of tectonic loading that best fit the observed plate flexure and normal faulting characteristics of the four trenches. The results reveal that a horizontal tensional force (HTF) for the Japan Trench is 33%, 50% and 60% smaller than those of the Mariana, Tonga and Izu-Bonin Trenches, respectively. The normal faults are modeled to penetrate to a maximum depth of 29, 23, 32 and 32 km below the sea floor for the Tonga, Japan, Izu-Bonin and Mariana Trenches, respectively, which is consistent with the depths of relocated normal faulting earthquakes in the Japan and Izu-Bonin Trenches. Moreover, it is argued that the calculated horizontal tensional force is generally positively correlated with the observed mean fault throw, while the integrated area of the reduction in the effective elastic thickness is correlated with the trench relief. These results imply that the HTF plays a key role in controlling the normal faulting pattern and that plate weakening can lead to significant increase in the trench relief. Key words: normal fault, geodynamic model, plate weakening, flexural bending, elasto-plastic deformation Citation: Zhou Zhiyuan, Lin Jian, Zhang Fan. 2018. Modeling of normal faulting in the subducting plates of the Tonga, Japan, Izu-Bonin and Mariana Trenches: implications for near-trench plate weakening. Acta Oceanologica Sinica, 37(11): 53–60, doi: 10.1007/s13131-0181146-z
1 Introduction The subduction zone is a critical component of the earth’s recycling system. During subduction, a downgoing plate sinks into the deep mantle and bends in response to its plate flexure, producing an extensional stress in the uppe
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