Multiple Seamount Subduction and Lithological Variability Possibly Control Pore Fluid Pressure and Shallow Slow Earthquake Activity in Nankai Trough off Muroto

IF 2.9 2区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Paul Caesar M. Flores, Shuichi Kodaira, Gaku Kimura, Kazuya Shiraishi, Yasuyuki Nakamura, Gou Fujie, Tetsuo No, Yuka Kaiho
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Abstract

The clustered distribution of shallow slow earthquakes in the Nankai Trough has been attributed to different factors such as seamount subduction, pore fluid pressure, fluid migration, and sediment input. However, there is still a lack of comprehensive understanding of how these factors interact to generate slow earthquakes. We examined the seismic reflection profiles crossing four subducted seamounts off Muroto to understand how they deform the accretionary wedge. Along-trough seismic reflection profiles within the accretionary wedge were also used to infer the lithology of the underthrusted sediments. The seamounts are at different stages of subduction and their associated underplated sediments were identified. Comparison with published sandbox models indicates that the underplated sediments comprise fluid-rich trench fill sediments. Negative polarity decollement and transparent underthrust are observed off Muroto. The transparent underthrust is interpreted as mudstone, while stratified underthrust sediments in other regions are interpreted as turbidites. Comparing with previous numerical simulations, we propose the following deformational history: (a) subduction of the first seamount resulted in underplating of a large volume of fluid-rich trench fill sediments, (b) the underplated sediments are undergoing horizontal compression from subsequent subduction of the three seamounts resulting in high pore pressure consistent with previously reported low velocity zones, and (c) the horizontal compression may also result in fluid expulsion and these fluids migrate updip and get trapped because the mudstones serve as an impermeable cap. This mechanism accounts the aforementioned factors associated with slow earthquakes and likely controls the clustered distribution off Muroto.

Abstract Image

多海山俯冲作用和岩性变异可能控制着南开海槽孔隙流体压力和浅层慢震活动
南海海槽浅层慢地震的群集分布被认为是由海山俯冲、孔隙流体压力、流体迁移和沉积物输入等不同因素造成的。然而,人们对这些因素如何相互作用产生慢震仍缺乏全面的了解。我们研究了穿过室户附近四座俯冲海山的地震反射剖面,以了解它们是如何使增生楔变形的。我们还利用增生楔内的沿槽地震反射剖面推断了下推沉积物的岩性。海山处于不同的俯冲阶段,与之相关的下推沉积物也已确定。与已公布的沙箱模型比较表明,下伏沉积物包括富含流体的海沟填充沉积物。在室户附近观测到了负极性解理和透明的下推。透明的下伏沉积物被解释为泥岩,而其他地区的层状下伏沉积物则被解释为浊积岩。与之前的数值模拟相比,我们提出了以下变形历史:(a)第一座海山的俯冲导致大量富含流体的海沟充填沉积物下伏,(b)下伏沉积物在三座海山的后续俯冲中受到水平压缩,导致孔隙压力高,与之前报告的低速区一致,以及(c)水平压缩也可能导致流体排出,由于泥岩作为不透水的顶盖,这些流体向上迁移并被困住。这一机制说明了与慢速地震有关的上述因素,并可能控制着室户附近的群集分布。
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来源期刊
Geochemistry Geophysics Geosystems
Geochemistry Geophysics Geosystems 地学-地球化学与地球物理
CiteScore
5.90
自引率
11.40%
发文量
252
审稿时长
1 months
期刊介绍: Geochemistry, Geophysics, Geosystems (G3) publishes research papers on Earth and planetary processes with a focus on understanding the Earth as a system. Observational, experimental, and theoretical investigations of the solid Earth, hydrosphere, atmosphere, biosphere, and solar system at all spatial and temporal scales are welcome. Articles should be of broad interest, and interdisciplinary approaches are encouraged. Areas of interest for this peer-reviewed journal include, but are not limited to: The physics and chemistry of the Earth, including its structure, composition, physical properties, dynamics, and evolution Principles and applications of geochemical proxies to studies of Earth history The physical properties, composition, and temporal evolution of the Earth''s major reservoirs and the coupling between them The dynamics of geochemical and biogeochemical cycles at all spatial and temporal scales Physical and cosmochemical constraints on the composition, origin, and evolution of the Earth and other terrestrial planets The chemistry and physics of solar system materials that are relevant to the formation, evolution, and current state of the Earth and the planets Advances in modeling, observation, and experimentation that are of widespread interest in the geosciences.
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