Flexure of the outer rise of the South Sumatra-Java Trench Segment： Lithospheric deformation at the subduction front simulated by geoid undulation

LIU Hongqin; SUN Weitao; YANG Yining; ZHAO Lihong; LING Zilong; WU Shiguo

doi:10.3969/j.issn.1001-909X.2026.02.005

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Journal of Marine Sciences ›› 2026, Vol. 44 ›› Issue (2) : 43-50. DOI: 10.3969/j.issn.1001-909X.2026.02.005

Flexure of the outer rise of the South Sumatra-Java Trench Segment： Lithospheric deformation at the subduction front simulated by geoid undulation

LIU Hongqin ¹ ,
SUN Weitao ² ,
YANG Yining ¹ ,
ZHAO Lihong ¹^,³^,^* ,
LING Zilong ¹ ,
WU Shiguo ⁴

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Abstract

The Indian Ocean subduction zone is one of the most active plate boundaries in the world and an important region for studying plate subduction. While many studies have examined the structure and evolution in the subduction zone， research on lithospheric flexure along the trench’s oceanward slope remains relatively limited. To clarify the characteristics of lithospheric flexure during subduction of the India-Australia Plate and its geodynamic implications， this study takes the South Sumatra-Java Trench as the research area for flexural modeling. Based on crustal thickness， geoid undulation， and bathymetric data， the lithospheric flexures of the eastern， central， and western segments of the South Sumatra-Java Trench were simulated. Using nonlinear least-squares fitting， we obtained the flexural characteristics and lithosphere effective elastic thickness （T_e） of each segment’s oceanward slope. The simulation results indicate that the flexure zone lies roughly between 16-76 km from the trench axis， with an amplitude of 68-192 m， and T_e of 20-34 km. T_e is the largest in the central segment and smaller in the eastern and western segments. T_e in the eastern segment is slightly larger than that in the western segment. The flexure of the trench exhibits significant spatial variability， primarily controlled by distinct geological and tectonic factors. The low T_e in the eastern segment is mainly attributed to lithospheric weakening caused by thermal upwelling from the lower mantle. The high T_e in the central segment indicates that its lithosphere is generally more rigid； however， influenced by local structures such as the Roo Rise and seamount emplacement， stress concentration at the plate forebulge leads to large flexural amplitudes in some profiles. The low T_e in the western segment may be related to reduced lithospheric strength associated with a young plate， stronger tectonic activity， and fluid effects. Nevertheless， because this segment is characterized by a lower subduction rate， shallower slab descent， and limited extensional deformation， its overall flexural response remains comparatively weak.

Key words

geoid undulation / flexure / effective elastic thickness / Java Trench / South Sumatra Trench / elastic thin plate model / plate subduction / outer rise belt

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LIU Hongqin , SUN Weitao , YANG Yining , et al . Flexure of the outer rise of the South Sumatra-Java Trench Segment： Lithospheric deformation at the subduction front simulated by geoid undulation[J]. Journal of Marine Sciences. 2026, 44(2): 43-50 https://doi.org/10.3969/j.issn.1001-909X.2026.02.005

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