Deformation Process and Mechanism of the Frontal Megathrust at the Nankai Subduction Zone

Kimura, Gaku; Hamada, Yohei; Yabe, Suguru; Yamaguchi, Asuka; Fukuchi, Rina; Kido, Yukari; Maeda, Lena; Toczko, S.; Okuda, H.; Ogawa, Norio; Morioka, Hiroshi; Ujiie, Kohtaro; Saffer, D. M.

doi:10.1029/2021gc009855

Cited by 2 publications

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References 34 publications

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“…A forearc basin is developed in the upper slope named the Muroto Basin in the west and the Kumano Basin east of the Shionomisaki canyon (Figure 2a). As the detailed morphology of the inner slope in this area was reported by Kimura et al (2022), we describe the outer slope south of the outer ridge in this paper. The outer slope is subdivided into four areas from I to IV (Figure 2a), divided by morphological breaks normal to the strike of troughparallel ridge-crests (labeled ① to ④) and intervening basins.…”

Section: Ocean Floor Topography Of the Outer Slopementioning

confidence: 92%

“…The base of the lower slope of the forearc in subduction zones generally coincides with the deformation front of the upper plate. The deformation front in accretionary margins is the seaward-most extent of deformation associated with the plate boundary megathrust as documented by drilling in the Nankai Trough off Muroto (Moore et al, 2001;Taira et al, 1992) and off Kumano (Fabbri et al, 2020;Kimura et al, 2011Kimura et al, , 2022Sakaguchi et al, 2011;Screaton et al, 2009). In this paper, we present analyses of structural features around the deformation front and the frontal thrust using both legacy and new 2D seismic reflection data sets.…”

Section: Geologic Structure Around the Deformation Front In Eastern A...mentioning

confidence: 99%

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

Kimura,

Shiraishi,

Nakamura

et al. 2024

Geochem Geophys Geosyst

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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.

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Section: Ocean Floor Topography Of the Outer Slopementioning

confidence: 92%

Section: Geologic Structure Around the Deformation Front In Eastern A...mentioning

confidence: 99%

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

Kimura,

Shiraishi,

Nakamura

et al. 2024

Geochem Geophys Geosyst

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A review of shallow slow earthquakes along the Nankai Trough

Takemura,

Hamada,

Okuda

et al. 2023

Earth Planets Space

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Slow earthquakes occur at deep and shallow plate boundaries along the Nankai Trough. Deep slow earthquakes are continuously distributed along the 30–40 km depth contours of the upper surface of the subducted Philippine Sea Plate. In contrast, shallow slow earthquakes occur in limited regions: Hyuga-nada, off Cape Muroto, and southeast off the Kii Peninsula. This review provides an overview of the up-to-date seismological, geodetic, geological, and experimental results in the shallow Nankai area for a unified understanding of the spot-like occurrence of shallow slow earthquakes. Shallow slow earthquakes tend to be distributed in transitional regions between the frictionally locked and stably sliding zones on the plate boundary. Based on geological and experimental studies, the lithology of incoming sediments and their friction coefficients can be variable along the Nankai Trough. Laboratory friction experiments revealed that sediments under shallow plate boundary conditions often exhibit positive (a − b) values, while negative (a − b) is possible via several processes. Subducted seamounts create complex fracture networks and stress shadows in their surrounding areas; however, not all subducted seamounts are related to shallow slow earthquake activities. This incomplete correlation suggests that alternative factors are required to explain the spot-like distribution of shallow slow earthquakes in the Nankai subduction zone. High pore fluid pressure conditions around shallow slow earthquake zones were interpreted based on seismological structural studies. In addition, ambient noise monitoring revealed temporal changes in seismic velocity structures associated with shallow slow earthquake migrations. This result suggests a close link between pore fluid migration and shallow slow earthquake episodes. Because transient changes in pore fluid pressure can lead to various slip behaviors, the episodic migration of pore fluid around the plate boundary could promote shallow slow earthquake activity along the Nankai Trough. Graphical Abstract

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Deformation Process and Mechanism of the Frontal Megathrust at the Nankai Subduction Zone

Cited by 2 publications

References 34 publications

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

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

A review of shallow slow earthquakes along the Nankai Trough

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