JpGU-AGU Joint Meeting 2020

Presentation information

[J] Oral

S (Solid Earth Sciences ) » S-CG Complex & General

[S-CG66] Ocean Floor Geoscience

convener:Kyoko Okino(Atmosphere and Ocean Research Institute, The University of Tokyo)

[SCG66-12] Effects of surface friction of subducting seamount on topographic evolution of the overriding accretionary prism: insights from sandbox experiment

*Yuichi Okuma1,2, Hiroaki Koge4, Yasuhiro Yamada3, Juichiro Ashi2,1, Asuka Yamaguchi1 (1.Atmosphere and Ocean Research Institute, the University of Tokyo, 2.Department of Natural Environmental Studies, Graduate School of Frontier Science, the University of Tokyo, 3.Japan Agency for Marine-Earth Science and Technology, 4.The National Institute of Advanced Industrial Science and Technology)

Keywords:Sandbox experiment, Image analysis, Seamount subduction, Nankai accretionary prism off Muroto

Topographic highs such as seamount or ridge widely exist on the seafloor, and subduct beneath the upper plates. These topographic highs may trigger large seafloor landslides or cause structural and physical heterogeneities in the upper plate. Many studies thus tried to understand those effects of seamount subduction by using geologic data such as seismic profiles, drilled cores, and modeling techniques such as numerical simulations and analog experiments (e.g., Barker et al., 2018; Collot et al., 2001; Bell et al., 2014; Dominguez et al., 1998, 2000; Ruh et al., 2016; Ellies et al., 2015). Dominguez et al. (1998) performed the analog experiments using sand to see the effects of seamount subduction on the accretionary prism, and reported that subducting seamount disturbs shallow portion of an accretionary prism by forming a unique structure called “fracture network” composed of many reverse, strike-slip and normal faults around the seamount. Since they only recorded the surface deformation process by using a video camera, the spatial and temporal resolution of the fracture network was not sufficient.

In this study, we ran analog experiments in order to examine detailed topographic evolution and surface deformation of an accretionary prism due to seamount subduction. Digital Image Correlation (DIC), an image analysis method, was applied to surface observation, after success of recent applications of this technique to sandbox experiment to extract detailed and quantitative information (e.g., Adam et al., 2005; Yamada et al., 2006; Dotare et al., 2016; Koge et al., 2018). In this study, this technique was mainly used for visualization of the fault activity with seamount subduction.

Two seamount models with different surface friction, smooth (low friction) and rough (high friction) surface models, were used to investigate the response to the upper plate. The results suggest four findings: (1) large strike-slip faulting described in Dominguez et al (1998) were not observed, (2) the topographically curved region formed by subduction of smooth surface seamount recovered earlier than subduction of rough surface seamount, (3) the horizontally deformed area was within ± 10% of the radius of the seamount, (4) the splay fault, branched from décollement at landward edge of the rough surface seamount, continued the activity for longer time than the smooth surface seamount.

In this presentation, we will also report application to the natural example where topographic features downgoing and curvature zone exists in the Nankai accretionary prism off Muroto.