Frontal Thrust Ramp-Up and Slow Earthquakes Due To Underthrusting of Basement High in the Nankai Trough

IF 2.9 2区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
G. Kimura, K. Shiraishi, Y. Nakamura, S. Kodaira, G. Fujie, R. Arai, G. F. Moore
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Abstract

Recently, integrated geophysical-geological surveys in the Nankai subduction zone in Japan have revealed that slow earthquakes repeatedly occur beneath the outer wedge of the forearc. During December 2020 to February 2021, clustered slow earthquakes propagated around the frontal thrust of the accretionary wedge. The frontal thrust ramps up from the basal décollement and slips over trench-filling sediment along the landward edge of the Nankai trough floor. Here, the Paleo-Zenisu ridge has been subducted beneath the inner-outer slope border. In addition, ocean floor topography and geologic structure revealed by seismic reflection surveys completed before 2022 document that the basement of the Philippine Sea Plate beneath the frontal thrust has a seamount and a horst-like basement high. The northern edge of the basement high is located at the ramp-up position of the frontal thrust. The 2020–2021 clustered slow earthquakes started at the Paleo-Zenisu ridge and propagated to the topographic highs beneath the deformation front. Considering that the relative plate convergence between the upper Amurian Plate of the Nankai forearc and the subducting Philippine Sea Plate is ∼6.0 cm/year, the basement high at the deformation front has uplifted the frontal crest of the wedge at an average rate of 2.7–5.7 mm/year for several tens to hundred thousand years. These rates are among some of the highest rock uplift rates measured in the world. The slow earthquakes in the off-Kumano Nankai Trough in 2020–2021 are a snapshot of a “living” Nankai frontal thrust during the megathrust interseismic period.

Abstract Image

南海海槽基底高地的下推导致的正面推力上升和慢速地震
最近,在日本南海俯冲带进行的地球物理-地质综合调查显示,在前弧的外楔之下反复发生慢速地震。2020 年 12 月至 2021 年 2 月期间,在增生楔的正面推力周围发生了群集慢震。前推力从基底解理上升,沿南海槽底向陆地边缘滑过海沟填充沉积物。在这里,古天鹅洲海脊被俯冲到内外侧坡边界之下。此外,2022 年之前完成的地震反射勘探所揭示的海底地形和地质结构表明,正面推力下方的菲律宾海板块基底有一个海山和一个角状基底高地。基底高地的北部边缘位于正面推力的上升位置。2020-2021 年的群集慢震始于古天鹅洲海脊,并向变形前沿下方的地形高地传播。考虑到南海前弧的上安室板块与俯冲的菲律宾海板块之间的相对板块辐合为 ∼6.0 厘米/年,变形前沿的基底高地以平均 2.7-5.7 毫米/年的速度抬升了楔形前沿顶峰,时间长达数万至数十万年。这些速度是世界上测得的最高岩石隆起速度之一。2020-2021 年在熊野南海海槽附近发生的缓慢地震是大地壳间震时期 "活着的 "南海正面推力的缩影。
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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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