Heterogeneous Sediment Input at the Nankai Trough Subduction Zone: Implications for Shallow Slow Earthquake Localization

Tilley, H.; Moore, Gregory F.; Underwood, Michael B.; Hernández-Molina, F. Javier; Yamashita, M; Kodaira, Shuichi; Nakanishi, Ayako

doi:10.1029/2021gc009965

Cited by 12 publications

(15 citation statements)

References 134 publications

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“…Depressions with a NNW‐SSE strike near the trough axis and on the incoming Philippine Sea plate appear in our basement map (features E and F in Figure 3a). These depressions represent grabens, formed during the formation of the Philippine Sea plate (e.g., Kimura et al., 2021), that are filled with thick sediments (e.g., Ike et al., 2008; Tilley et al., 2021).…”

Section: Resultsmentioning

confidence: 99%

Structural Anomaly at the Boundary Between Strong and Weak Plate Coupling in the Central‐Western Nankai Trough

Nakamura

Shiraishi

Fujie

et al. 2022

Geophysical Research Letters

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Megathrust earthquakes in subduction zones generate strong ground motion and destructive tsunamis that cause devastating damage in populated areas. The updip limit of the megathrust rupture zone constrains the potential size of these earthquakes. Massive tsunamis are often caused by seafloor displacement in the shallow portion of subduction zones during megathrust earthquakes, such as the 2011 Tohoku earthquake (e.g., Satake et al., 2013;Yamazaki et al., 2018). Studies of the shallow subduction zone thus are indispensable to understanding the megathrust rupture process and also subduction zone tectonics.The shallower part of subduction zones can be divided into two or three regions by their characteristic slip behavior, such as unstable, stable, and conditionally stable slip (e.g., Bilek & Lay, 2002). Recently, Obara and Kato (2016) presented a model of the Nankai Trough subduction zone off southwestern Japan based on the characteristic time scale of seismological and geodetic events. Their model has three regions in the shallow subduction zone; at increasing depths landward from the trench axis, these are the stable sliding zone, transition zone, and seismogenic zone. In the stable sliding zone, the plate boundary fault creeps without seismic ruptures. In the seismogenic zone, megathrust earthquakes rupture the plate boundary fault, and coupling is strong on the plate boundary. The transition zone is where intermittent slip events such as slow earthquakes occur. Coupling is relatively weak in the transition zone. The boundary between the seismogenic and transition zones corresponds to the updip edge of the rupture area of great earthquakes; therefore, it is important to understand the structural factors defining this boundary.The Nankai Trough subduction zone, where the Philippine Sea plate subducts beneath the Amur plate, has experienced multiple great earthquakes (Nankai earthquakes) and tsunamis in the last millennium at recurrence intervals of ∼100-200 yrs (Ando, 1975). The latest Nankai earthquake occurred in 1946 in the western Nankai Trough. Tsunami inversions revealing the slip distribution during this earthquake (Baba & Cummins, 2005;

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Section: Resultsmentioning

confidence: 99%

Structural Anomaly at the Boundary Between Strong and Weak Plate Coupling in the Central‐Western Nankai Trough

Nakamura

Shiraishi

Fujie

et al. 2022

Geophysical Research Letters

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“…On the other hand, strong ocean currents offshore Japan (for example, the Kuroshio Current) have been recognized as a dominant agent of routing based on interpretations of clay mineral provenance (Underwood & Fergusson, 1996; Underwood & Guo, 2018). The recent discovery of contourite drifts immediately seaward of the trench depended on acquisition of high‐quality, high‐resolution seismic reflection data (Tilley et al ., 2021). If one considers both Nankai and Hikurangi, it now seems apparent that occurrences of contourites and contourite–turbidite hybrids are more widespread in modern subduction zones than what was previously thought.…”

Section: Discussionmentioning

confidence: 99%

“…Mulder et al ., 2006; Huppertz & Piper, 2010; Brackenridge et al ., 2013; Gruetzner et al ., 2016; Sansom, 2018; Thieblemont et al ., 2019; Fuhrmann et al ., 2020; Mencaroni et al ., 2021; Miramontes et al ., 2021). That global bias has led to a perception that contourites are unusual or nonexistent in subduction zones, but recent studies of the Nankai system suggest that the perception is probably flawed (Tilley et al ., 2021). Refinements of actualistic facies models for deep‐sea trenches are necessary to advance the broader goals of recognizing facies equivalents and predicting the stratigraphic architecture of ancient (deep‐time) systems.…”

Section: Introductionmentioning

confidence: 99%

Composition of fine‐grained sediment in the Hikurangi Trough: Evidence for intermingling among axial gravity flows, transverse gravity flows and margin‐parallel ocean currents

Underwood

2023

Sedimentology

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The International Ocean Discovery Program cored five sites during Expeditions 372 and 375 to investigate the Hikurangi margin, offshore Poverty Bay, North Island, New Zealand. Trench‐wedge deposits were recovered at Site U1520, and the frontal accretionary prism was cored at Site U1518. Based on X‐ray diffraction analyses of the clay‐sized fraction, illite and smectite are the dominant clay minerals. Compositional scatter is unusually large, and a well‐defined mixing trend is evident between illite‐rich and smectite‐rich end members. The proportion of smectite ranges from 9 to 59 wt.% at Site U1518 and from 12 to 62 wt.% at Site U1520. Nearby slope deposits at Sites U1517 and U1519 are more homogeneous, with consistently higher proportions of smectite. The East Cape Current is probably responsible for transporting smectite‐rich suspensions towards the south‐west from sources that include the Taupo Volcanic Zone. Illite‐rich muds require different sources and different routing paths to the trench. Some suspended sediment probably originated in the Waipaoa watershed on the North Island, entering the trench via Māhia Canyon. Other gravity flows probably started in Kaikōura Canyon or Cook Strait and moved towards the north‐east, down the trench's axial channel. The influence of turbidity currents on clay composition changes with water depth, as do the effects of reworking by contour currents and the role of passive hemipelagic settling. The broad continuum of clay compositions in the trench is enhanced by variable amounts of mixing among multiple ocean currents and fluctuating durations of suspension within a bottom nepheloid layer. That complexity deviates from the paradigm of turbidite‐dominated trench wedges. The margin's compositional diversity also complicates the goal of predicting or modelling three‐dimensional variations in frictional, geotechnical and hydrogeological properties. Those lithological properties are important because they affect slope stability along strike and changes in fault‐slip behaviour along the subduction interface.

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“…Very low frequency earthquakes (VLFE) and tremors, which are types of seismic slow earthquakes, have been detected in the shallow megathrust of the Nankai Trough (<30 km) and show a clustered distribution (Figure 1) (Nakano et al., 2018; Ogiso & Tamaribuchi, 2022; Takemura, Matsuzawa, et al., 2019; Takemura, Noda, et al., 2019; Takemura, Baba, et al., 2022; Takemura, Obara, et al., 2022; Tamaribuchi et al., 2022). Previous studies have suggested possible factors affecting the spatial distribution of VLFEs and tremors such as the presence of a subducted seamount (Baba et al., 2023; Sun et al., 2020; Takemura, Matsuzawa, et al., 2019), pore fluid pressure (Hirose et al., 2021; Kitajima & Saffer, 2012; Kodaira et al., 2004), sediment thickness and lithology (Ike et al., 2008; Park and Jamali‐Hondori, 2023; Tilley et al., 2021) and slip‐deficit rate (Yokota et al., 2016).…”

Section: Introductionmentioning

confidence: 99%

Link Between Geometrical and Physical Property Changes Along Nankai Trough With Slow Earthquake Activity Revealed by Dense Reflection Survey

Flores,

Kodaira,

Kimura

et al. 2024

Geophysical Research Letters

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We examined the possible factors affecting the spatial distribution of very low frequency earthquakes and tremors in the shallow megathrust of Nankai Trough (<30 km) using a dense network of prestack depth migrated profiles at the frontal wedge. Geometrical parameters examined were decollement roughness, taper angle, and underthrust thickness. Physical properties such as effective basal friction (μb) and pore pressure ratio (λ*) were calculated from the taper angle and p‐wave velocity. Regions of low λ* (0.39 ± 0.08) and smooth decollement showed no slow earthquake activity. In contrast, high activity of slow earthquakes was observed in areas with a rough decollement due to the presence of subducted seamounts or bathymetric highs. The low taper angle (3.8°) off Muroto where slow earthquakes also occur translates to a wide zone of low μb (0.21 ± 0.06) and high λ* (0.66 ± 0.06). However, our results also show that slow earthquakes don't always occur in areas with high λ*.

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Heterogeneous Sediment Input at the Nankai Trough Subduction Zone: Implications for Shallow Slow Earthquake Localization

Cited by 12 publications

References 134 publications

Structural Anomaly at the Boundary Between Strong and Weak Plate Coupling in the Central‐Western Nankai Trough

Structural Anomaly at the Boundary Between Strong and Weak Plate Coupling in the Central‐Western Nankai Trough

Composition of fine‐grained sediment in the Hikurangi Trough: Evidence for intermingling among axial gravity flows, transverse gravity flows and margin‐parallel ocean currents

Link Between Geometrical and Physical Property Changes Along Nankai Trough With Slow Earthquake Activity Revealed by Dense Reflection Survey

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