首页> 外文期刊>Journal of geophysical research. Solid earth: JGR >The South Ecuador subduction channel: Evidence for a dynamic mega‐shear zone from 2D fine‐scale seismic reflection imaging and implications for material transfer
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The South Ecuador subduction channel: Evidence for a dynamic mega‐shear zone from 2D fine‐scale seismic reflection imaging and implications for material transfer

机译:南厄瓜多尔俯冲通道:来自二维精细地震反射成像的动态巨型剪切带的证据及其对物质转移的影响

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Tectonic processes that control the transition from poorly consolidated sediment entering the subduction channel (SC) to the seismogenic zone are documented using seismic imaging. We applied pre‐stack depth migration and a post‐processing sequence to a seismic reflection line acquired across the Ecuador convergent margin to obtain a 2D‐quantitative image of the first ~24 km of the SC. Structural interpretation shows that the SC consists of a 630–1150‐m‐thick, low‐velocity, continuous sheet of sediment that dips ~6° landward and undergoes shear deformation. The long sheet is bounded at top and bottom by decollement thrusts, and developed over time Riedel shears and basal thrust faulting and folding downdip, pointing to a dynamic mega‐shear zone. Modeling the strong uppermost and basal SC reflectors reveals that they are associated with 40–80‐mthick, 50–350 m/s, low‐velocity perturbations layers inferred to be fluid rich and mechanically weak. A fine‐scale velocity model shows two anomalously low‐Vp areas in the long sheet, advocating patches of over‐pressured fluids. Evidence for Vp variations along the upper‐plate foundation suggests either underplated bodies or a fluid‐damage zone. A simple temporal reconstruction indicates that underthrusting the long sheet initiated >450 kyr ago and interrupted ~54 ± 13 kyr ago, when frontal accretion resumed. During this transient evolution, the SC boundaries revealed highly unstable as most of the SC was underplated while down going plate material may have been sheared off and incorporated to the SC.
机译:使用地震成像记录了控制从进入俯冲河道(SC)的固结不良的沉积物到地震发生带的过渡的构造过程。我们将叠前深度偏移和后处理序列应用于横跨厄瓜多尔会聚边界的地震反射线,以获得南北前约24 km的二维定量图像。结构解释表明,SC由厚度为630-1150m的低速连续沉积物组成,向内倾斜约6°并经历剪切变形。长片在顶部和底部受到弯折推力的限制,并随时间发展Riedel剪切力,基底推力断层和折叠下倾,指向一个动态的大剪切带。对最强的最上层和基础SC反射器进行建模后发现,它们与40-80微米厚,50-350 m / s的低速扰动层有关,这些层被推断为流体丰富且机械强度较弱。精细的速度模型显示了长片中的两个异常低Vp区域,提倡出现超压流体斑块。沿上板基础的Vp变化的证据表明,板下体或流体破坏带。一个简单的时间重建表明,对长片的逆冲作用始于> 450年前,并在〜54±13年前中断,这时额积又恢复了。在此瞬态演变过程中,SC边界显示出高度不稳定,因为大多数SC底镀,而向下的板材可能已被剪切掉并掺入了SC中。

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