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Arai R, Miura S, Nakamura Y, Fujie G, Kodaira S, Kaiho Y, Mochizuki K, Nakata R, Kinoshita M, Hashimoto Y, Hamada Y, Okino K. Upper-plate conduits linked to plate boundary that hosts slow earthquakes. Nat Commun 2023; 14:5101. [PMID: 37730797 PMCID: PMC10511545 DOI: 10.1038/s41467-023-40762-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Accepted: 08/07/2023] [Indexed: 09/22/2023] Open
Abstract
In shallow subduction zones, fluid behavior impacts various geodynamic processes capable of regulating slip behaviors and forming mud volcanoes. However, evidence of structures that control the fluid transfer within an overriding plate is limited and the physical properties at the source faults of slow earthquakes are poorly understood. Here we present high-resolution seismic velocity models and reflection images of the Hyuga-nada area, Japan, where the Kyushu-Palau ridge subducts. We image distinct kilometer-wide columns in the upper plate with reduced velocities that extend vertically from the seafloor down to 10-13 km depth. We interpret the low-velocity columns as damaged zones caused by seamount subduction and suggest that they serve as conduits, facilitating vertical fluid migration from the plate boundary. The lateral variation in upper-plate velocity and seismic reflectivity along the plate boundary correlates with the distribution of slow earthquakes, indicating that the upper-plate drainage system controls the complex pattern of seismic slip at subduction faults.
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Affiliation(s)
- Ryuta Arai
- Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, 236-0001, Japan.
| | - Seiichi Miura
- Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, 236-0001, Japan
| | - Yasuyuki Nakamura
- Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, 236-0001, Japan
| | - Gou Fujie
- Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, 236-0001, Japan
| | - Shuichi Kodaira
- Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, 236-0001, Japan
| | - Yuka Kaiho
- Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, 236-0001, Japan
| | - Kimihiro Mochizuki
- Earthquake Research Institute, The University of Tokyo, 1-1-1 Yayoi Bunkyo-ku, Tokyo, 113-0032, Japan
| | - Rie Nakata
- Earthquake Research Institute, The University of Tokyo, 1-1-1 Yayoi Bunkyo-ku, Tokyo, 113-0032, Japan
- Lawrence Berkeley National Laboratory, Berkeley, USA
| | - Masataka Kinoshita
- Earthquake Research Institute, The University of Tokyo, 1-1-1 Yayoi Bunkyo-ku, Tokyo, 113-0032, Japan
| | - Yoshitaka Hashimoto
- Faculty of Science and Technology, Kochi University, Akebonocho 2-5-1, Kochi, 780-8520, Japan
| | - Yohei Hamada
- Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 200 Monobe Otsu Nankoku, Kochi, 783-8502, Japan
| | - Kyoko Okino
- Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha Kashiwa, Chiba, 277-8564, Japan
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2
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Chesley C, Naif S, Key K. Characterizing the porosity structure and gas hydrate distribution at the southern Hikurangi Margin, New Zealand from offshore electromagnetic data. GEOPHYSICAL JOURNAL INTERNATIONAL 2023; 234:2412-2429. [PMID: 37416748 PMCID: PMC10319633 DOI: 10.1093/gji/ggad243] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2023] [Revised: 11/14/2022] [Accepted: 06/14/2023] [Indexed: 07/08/2023]
Abstract
The dynamics of accretionary prisms and the processes that take place along subduction interfaces are controlled, in part, by the porosity and fluid overpressure of both the forearc wedge and the sediments transported to the system by the subducting plate. The Hikurangi Margin, located offshore the North Island of New Zealand, is a particularly relevant area to investigate the interplay between the consolidation state of incoming plate sediments, dewatering and fluid flow in the accretionary wedge and observed geodetic coupling and megathrust slip behaviour along the plate interface. In its short geographic extent, the margin hosts a diversity of properties that impact subduction processes and that transition from north to south. Its southernmost limit is characterized by frontal accretion, thick sediment subduction, the absence of seafloor roughness, strong interseismic coupling and deep slow slip events. Here we use seafloor magnetotelluric (MT) and controlled-source electromagnetic (CSEM) data collected along a profile through the southern Hikurangi Margin to image the electrical resistivity of the forearc and incoming plate. Resistive anomalies in the shallow forearc likely indicate the presence of gas hydrates, and we relate deeper forerarc resistors to thrust faulting imaged in colocated seismic reflection data. Because MT and CSEM data are highly sensitive to fluid phases in the pore spaces of seafloor sediments and oceanic crust, we convert resistivity to porosity to obtain a representation of fluid distribution along the profile. We show that porosity predicted by the resistivity data can be well fit by an exponential sediment compaction model. By removing this compaction trend from the porosity model, we are able to evaluate the second-order, lateral changes in porosity, an approach that can be applied to EM data sets from other sedimentary basins. Using this porosity anomaly model, we examine the consolidation state of the incoming plate and accretionary wedge sediments. A decrease in porosity observed in the sediments approaching the trench suggests that a protothrust zone is developing ∼25 km seaward of the frontal thrust. Our data also imply that sediments deeper in the accretionary wedge are slightly underconsolidated, which may indicate incomplete drainage and elevated fluid overpressures of the deep wedge.
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Affiliation(s)
- Christine Chesley
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
| | - Samer Naif
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA
| | - Kerry Key
- Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964-1000, USA
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3
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Gase AC, Bangs NL, Saffer DM, Han S, Miller PK, Bell RE, Arai R, Henrys SA, Kodaira S, Davy R, Frahm L, Barker DH. Subducting volcaniclastic-rich upper crust supplies fluids for shallow megathrust and slow slip. SCIENCE ADVANCES 2023; 9:eadh0150. [PMID: 37585538 PMCID: PMC10431706 DOI: 10.1126/sciadv.adh0150] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2023] [Accepted: 07/17/2023] [Indexed: 08/18/2023]
Abstract
Recurring slow slip along near-trench megathrust faults occurs at many subduction zones, but for unknown reasons, this process is not universal. Fluid overpressures are implicated in encouraging slow slip; however, links between slow slip, fluid content, and hydrogeology remain poorly known in natural systems. Three-dimensional seismic imaging and ocean drilling at the Hikurangi margin reveal a widespread and previously unknown fluid reservoir within the extensively hydrated (up to 47 vol % H2O) volcanic upper crust of the subducting Hikurangi Plateau large igneous province. This ~1.5 km thick volcaniclastic upper crust readily dewaters with subduction but retains half of its fluid content upon reaching regions with well-characterized slow slip. We suggest that volcaniclastic-rich upper crust at volcanic plateaus and seamounts is a major source of water that contributes to the fluid budget in subduction zones and may drive fluid overpressures along the megathrust that give rise to frequent shallow slow slip.
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Affiliation(s)
- Andrew C. Gase
- Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA
| | - Nathan L. Bangs
- Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA
| | - Demian M. Saffer
- Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA
| | - Shuoshuo Han
- Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA
| | - Peter K. Miller
- Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA
| | - Rebecca E. Bell
- Department of Earth Science and Engineering, Imperial College London, London, UK
| | - Ryuta Arai
- Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
| | | | - Shuichi Kodaira
- Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
| | - Richard Davy
- Department of Earth Science and Engineering, Imperial College London, London, UK
| | - Laura Frahm
- Department of Earth Science and Engineering, Imperial College London, London, UK
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4
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Shreedharan S, Saffer D, Wallace LM, Williams C. Ultralow frictional healing explains recurring slow slip events. Science 2023; 379:712-717. [PMID: 36795827 DOI: 10.1126/science.adf4930] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
Abstract
Plate motion on shallow subduction megathrusts is accommodated by a spectrum of tectonic slip modes. However, the frictional properties and conditions that sustain these diverse slip behaviors remain enigmatic. Frictional healing is one such property, which describes the degree of fault restrengthening between earthquakes. We show that the frictional healing rate of materials entrained along the megathrust at the northern Hikurangi margin, which hosts well-characterized recurring shallow slow slip events (SSEs), is nearly zero (<0.0001 per decade). These low healing rates provide a mechanism for the low stress drops (<50 kilopascals) and short recurrence times (1 to 2 years) characteristic of shallow SSEs at Hikurangi and other subduction margins. We suggest that near-zero frictional healing rates, associated with weak phyllosilicates that are common in subduction zones, may promote frequent, small-stress-drop, slow ruptures near the trench.
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Affiliation(s)
- Srisharan Shreedharan
- Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA.,Department of Geosciences, Utah State University, Logan, UT, USA
| | - Demian Saffer
- Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA.,Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA
| | - Laura M Wallace
- Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA.,GNS Science, Lower Hutt, New Zealand
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5
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Creep fronts and complexity in laboratory earthquake sequences illuminate delayed earthquake triggering. Nat Commun 2022; 13:6839. [PMID: 36369222 PMCID: PMC9652330 DOI: 10.1038/s41467-022-34397-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Accepted: 10/19/2022] [Indexed: 11/13/2022] Open
Abstract
Earthquakes occur in clusters or sequences that arise from complex triggering mechanisms, but direct measurement of the slow subsurface slip responsible for delayed triggering is rarely possible. We investigate the origins of complexity and its relationship to heterogeneity using an experimental fault with two dominant seismic asperities. The fault is composed of quartz powder, a material common to natural faults, sandwiched between 760 mm long polymer blocks that deform the way 10 meters of rock would behave. We observe periodic repeating earthquakes that transition into aperiodic and complex sequences of fast and slow events. Neighboring earthquakes communicate via migrating slow slip, which resembles creep fronts observed in numerical simulations and on tectonic faults. Utilizing both local stress measurements and numerical simulations, we observe that the speed and strength of creep fronts are highly sensitive to fault stress levels left behind by previous earthquakes, and may serve as on-fault stress meters. Laboratory earthquake experiments reproduce delayed earthquake triggering, similar to aftershocks, as a result of propagating slow slip fronts. The speed of the fronts can be highly sensitive to fault stress levels left behind by previous earthquakes.
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6
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Leah H, Fagereng Å. Inherited Heterogeneities Can Control Viscous Subduction Zone Deformation of Carbonates at Seismogenic Depths. GEOPHYSICAL RESEARCH LETTERS 2022; 49:e2022GL099358. [PMID: 36591572 PMCID: PMC9788063 DOI: 10.1029/2022gl099358] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Revised: 09/21/2022] [Accepted: 09/27/2022] [Indexed: 06/17/2023]
Abstract
This work links mineral-scale deformation mechanisms with structural evolution during subduction, providing examples showing how grain-scale heterogeneities facilitated viscous creep in calcite at nominally seismogenic temperatures. Carbonates commonly enter subduction zones, either highly concentrated in irregularly distributed sediments or as more distributed precipitates in seafloor volcanics. We present shear zones, localized in calcite veins formed during shallow subduction of calcareous sediment and seafloor volcanics, with viscous shear strains of ≥5. Shear strain localized because secondary phases and chemical variations maintained fine grain sizes in calcite aggregates, activating relatively rapid grain size-sensitive and frictional-viscous creep at temperatures (260 ± 10°C), cooler than predicted from extrapolation of experimental data. Creep at increased strain rates may limit elastic strain accumulation during interseismic periods, reducing the likelihood of large megathrust earthquakes. As shown here for calcite, common inherited natural heterogeneities may induce weakening of viscous mechanisms in other rocks, or at larger scales in the lithosphere.
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Affiliation(s)
- H. Leah
- Cardiff School of Earth and Ocean SciencesCardiff UniversityCardiffUK
| | - Å. Fagereng
- Cardiff School of Earth and Ocean SciencesCardiff UniversityCardiffUK
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7
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Rock and fault rheology explain differences between on fault and distributed seismicity. Nat Commun 2022; 13:5627. [PMID: 36163188 PMCID: PMC9512795 DOI: 10.1038/s41467-022-33373-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Accepted: 09/15/2022] [Indexed: 11/17/2022] Open
Abstract
Analysis of seismicity can illuminate active fault zone structures but also deformation within large volumes of the seismogenic zone. For the Mw 6.5 2016–2017 Central Italy seismic sequence, seismicity not only localizes along the major structures hosting the mainshocks (on-fault seismicity), but also occurs within volumes of Triassic Evaporites, TE, composed of alternated anhydrites and dolostones. These volumes of distributed microseismicity show a different frequency-magnitude distribution than on-fault seismicity. We interpret that, during the sequence, shear strain-rate increase, and fluid overpressure promoted widespread ductile deformation within TE that light-up with distributed microseismicity. This interpretation is supported by field and laboratory observations showing that TE background ductile deformation is complex and dominated by distributed failure and folding of the anhydrites associated with boudinage hydro-fracturing and faulting of dolostones. Our results indicate that ductile crustal deformation can cause distributed microseismicity, which obeys to different scaling laws than on-fault seismicity occurring on structures characterized by elasto-frictional stick-slip behaviour. A new study sheds light on earthquake physics, showing that lithological and rheological heterogeneities in the rocks composing the seismogenic layer strongly influence seismicity distributions and earthquake scaling laws.
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8
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Leah H, Fagereng Å, Groome N, Buchs D, Eijsink A, Niemeijer A. Heterogeneous Subgreenschist Deformation in an Exhumed Sediment-Poor Mélange. JOURNAL OF GEOPHYSICAL RESEARCH. SOLID EARTH 2022; 127:e2022JB024353. [PMID: 36250158 PMCID: PMC9540080 DOI: 10.1029/2022jb024353] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Revised: 08/04/2022] [Accepted: 08/09/2022] [Indexed: 05/26/2023]
Abstract
Many described subduction complexes (or mélanges) exhumed from seismogenic depths comprise thick, turbidite-dominated sequences with deformed zones containing clasts or boudins of more competent sandstone and/or basalt. In contrast, many active subduction zones have a relatively small thickness of sedimentary inputs (<2 km), turbidite sequences are commonly accreted rather than subducted, and the role of pelagic sediments and basalt (lavas and hyaloclastites) in the deforming zone near the plate interface at <20 km depth is poorly understood. Field investigation of Neoproterozoic oceanic sequences accreted in the Gwna Complex, Anglesey, UK, reveals repeated lenticular slices of variably sampled ocean plate stratigraphy (OPS) bounded by thin mélange-bearing shear zones. Mélange matrix material is derived from adjacent OPS lithologies and is either dominantly illitic, likely derived from altered siliciclastic sediment, or chloritic, likely derived from altered volcanics. In the illitic mélange, mutually cross-cutting phyllosilicate foliation and variably deformed chlorite-quartz-calcite veins suggest ductile creep was cyclically punctuated by transient, localized fluid pulses. Chlorite thermometry indicates the veins formed at 260 ± 10°C. In the chloritic mélange, recrystallized through-going calcite veins are deformed to shear strains of 4-5 within a foliated chlorite matrix, suggesting calcite veins in subducting volcanics may localize deformation in the seismogenic zone. Shear stress-strain rate curves constructed using existing empirical relationships in a simplified shear zone geometry predict that slip velocities varied depending on pore fluid pressure; models predict slow slip velocities preferentially by frictional sliding in chlorite, at pore fluid pressures greater than hydrostatic but less than lithostatic.
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Affiliation(s)
- H. Leah
- School of Earth and Environmental SciencesCardiff UniversityCardiffUK
| | - Å. Fagereng
- School of Earth and Environmental SciencesCardiff UniversityCardiffUK
| | - N. Groome
- School of Earth and Environmental SciencesCardiff UniversityCardiffUK
| | - D. Buchs
- School of Earth and Environmental SciencesCardiff UniversityCardiffUK
| | - A. Eijsink
- MARUM Center for Marine Environmental SciencesUniversity of BremenBremenGermany
- Department of Energy and Mineral Engineering and EMS Energy InstituteThe Pennsylvania State UniversityUniversity ParkPAUSA
| | - A. Niemeijer
- Department of Earth SciencesUtrecht UniversityHPT LaboratoryUtrechtThe Netherlands
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9
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Giuntoli F, Viola G. A likely geological record of deep tremor and slow slip events from a subducted continental broken formation. Sci Rep 2022; 12:4506. [PMID: 35296716 PMCID: PMC8927582 DOI: 10.1038/s41598-022-08489-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Accepted: 02/28/2022] [Indexed: 11/10/2022] Open
Abstract
Fluids in subduction zones play a key role in controlling seismic activity, drastically affecting the rheology of rocks, triggering mineral reactions, and lowering the effective stress. Fluctuating pore pressure is one important parameter for the switch between brittle and ductile deformation, thus impacting seismogenesis. Episodic tremor and slow slip events (ETS) have been proposed as a common feature of the geophysical signature of subduction zones. Their geological record, however, remains scanty. Only the detailed and further characterization of exhumed fossil geological settings can help fill this knowledge gap. Here we propose that fluctuating pore pressure linked to metamorphic dehydration reactions steered cyclic and ETS-related brittle and ductile deformation of continental crustal rocks in the subduction channel of the Apennines. Dilational shear veins and ductile mylonitic shear zones formed broadly coevally at minimum 1 GPa and 350 °C, corresponding to ~ 30-40 km depth in the subduction zone. We identify carpholite in Ca-poor metasediments as an important carrier of H2O to depths > 40 km in cold subduction zones. Our results suggest that the described (micro)structures and mineralogical changes can be ascribed to deep ETS and provide a useful reference for the interpretation of similar tectonic settings worldwide.
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Affiliation(s)
- Francesco Giuntoli
- Department of Biological, Geological and Environmental Sciences, Università degli Studi di Bologna, Bologna, Italy.
| | - Giulio Viola
- Department of Biological, Geological and Environmental Sciences, Università degli Studi di Bologna, Bologna, Italy
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10
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Hashimoto Y, Sato S, Kimura G, Kinoshita M, Miyakawa A, Moore GF, Nakano M, Shiraishi K, Yamada Y. Décollement geometry controls on shallow very low frequency earthquakes. Sci Rep 2022; 12:2677. [PMID: 35177710 PMCID: PMC8854613 DOI: 10.1038/s41598-022-06645-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2021] [Accepted: 02/03/2022] [Indexed: 11/09/2022] Open
Abstract
Recent studies have documented the occurrence of shallow very low frequency earthquakes (VLFE) in subduction zones. The heterogeneity of the materials or stresses that act on the plate interface results in the variable slip rate. Stress on the décollement can be controlled by the décollement geometry and the regional stress, which is also able to control the material properties. We determined the distribution of stress along the shallow portion of the décollement in the Nankai Trough using a three-dimensional (3D) seismic survey and regional stress analysis to construct maps of normalized slip tendency (Ts′) and dilation tendency (Td). Alignments of VLFEs trend parallel to the trends of \documentclass[12pt]{minimal}
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\begin{document}$${T}_{d}$$\end{document}Td. On the other hand, very low \documentclass[12pt]{minimal}
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\begin{document}$${T}_{d}$$\end{document}Td areas probably act as barriers that limit the number of VLFEs that can migrate towards the trench. Because the \documentclass[12pt]{minimal}
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\begin{document}$${T}_{d}$$\end{document}Td distributions are derived only from the décollement geometry and the regional stress without incorporating any data on sediment properties, the consistency between the trends suggests that the décollement geometry is the primary control on VLFE activity.
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Affiliation(s)
- Yoshitaka Hashimoto
- Department of Global Environment and Disaster Prevention, Faculty of Science and Technology, Kochi University, Akebonocho 2-5-1, Kochi, 780-8520, Japan.
| | - Shigeyuki Sato
- Department of Global Environment and Disaster Prevention, Faculty of Science and Technology, Kochi University, Akebonocho 2-5-1, Kochi, 780-8520, Japan
| | - Gaku Kimura
- Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, 236-0001, Japan
| | - Masataka Kinoshita
- Earthquake Research Institute, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
| | - Ayumu Miyakawa
- Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba City, Ibaraki, 305-8567, Japan
| | - Gregory F Moore
- Department of Earth Sciences, University of Hawai'i, Mānoa, 1680 East-West Road, Honolulu, HI, 96822, USA
| | - Masaru Nakano
- Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, 236-0001, Japan
| | - Kazuya Shiraishi
- Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, 236-0001, Japan
| | - Yasuhiro Yamada
- Department of Earth Resources Engineering, Graduate School of Engineering, Kyushu University, Motooka 774, Fukuoka, 819-0395, Japan
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11
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Bedford JD, Faulkner DR, Lapusta N. Fault rock heterogeneity can produce fault weakness and reduce fault stability. Nat Commun 2022; 13:326. [PMID: 35039494 PMCID: PMC8763890 DOI: 10.1038/s41467-022-27998-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Accepted: 12/15/2021] [Indexed: 11/09/2022] Open
Abstract
Geological heterogeneity is abundant in crustal fault zones; however, its role in controlling the mechanical behaviour of faults is poorly constrained. Here, we present laboratory friction experiments on laterally heterogeneous faults, with patches of strong, rate-weakening quartz gouge and weak, rate-strengthening clay gouge. The experiments show that the heterogeneity leads to a significant reduction in strength and frictional stability in comparison to compositionally identical faults with homogeneously mixed gouges. We identify a combination of weakening effects, including smearing of the weak clay; differential compaction of the two gouges redistributing normal stress; and shear localization producing stress concentrations in the strong quartz patches. The results demonstrate that geological heterogeneity and its evolution can have pronounced effects on fault strength and stability and, by extension, on the occurrence of slow-slip transients versus earthquake ruptures and the characteristics of the resulting events, and should be further studied in lab experiments and earthquake source modelling.
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Affiliation(s)
- John D Bedford
- Rock Deformation Laboratory, Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool, UK.
| | - Daniel R Faulkner
- Rock Deformation Laboratory, Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool, UK
| | - Nadia Lapusta
- Department of Mechanical and Civil Engineering, Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA, USA.,Seismological Laboratory, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
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12
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Perez‐Silva A, Kaneko Y, Savage M, Wallace L, Li D, Williams C. Segmentation of Shallow Slow Slip Events at the Hikurangi Subduction Zone Explained by Along-Strike Changes in Fault Geometry and Plate Convergence Rates. JOURNAL OF GEOPHYSICAL RESEARCH. SOLID EARTH 2022; 127:e2021JB022913. [PMID: 35860634 PMCID: PMC9285732 DOI: 10.1029/2021jb022913] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/28/2021] [Revised: 12/22/2021] [Accepted: 01/06/2022] [Indexed: 06/15/2023]
Abstract
Over the last two decades, geodetic and seismic observations have revealed a spectrum of slow earthquakes along the Hikurangi subduction zone in New Zealand. Of those, shallow slow slip events (SSEs) that occur at depths of less than 15 km along the plate interface show a strong along-strike segmentation in their recurrence intervals, which vary from ∼1 yr from offshore Tolaga Bay in the northeast to ∼5 yr offshore Cape Turnagain ∼300 km to the southwest. To understand the factors that control this segmentation, we conduct numerical simulations of SSEs incorporating laboratory-derived rate-and-state friction laws with both planar and non-planar fault geometries. We find that a relatively simple model assuming a realistic non-planar fault geometry reproduces the characteristics of shallow SSEs as constrained by geodetic observations. Our preferred model captures the magnitudes and durations of SSEs, as well as the northward decrease of their recurrence intervals. Our results indicate that the segmentation of SSE recurrence intervals is favored by along-strike changes in both the plate convergence rate and the downdip width of the SSE source region. Modeled SSEs with longer recurrence intervals concentrate in the southern part of the fault (offshore Cape Turnagain), where the plate convergence rate is lowest and the source region of SSEs is widest due to the shallower slab dip angle. Notably, the observed segmentation of shallow SSEs cannot be reproduced with a simple planar fault model, which indicates that a realistic plate interface is an important factor to account for in modeling SSEs.
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Affiliation(s)
- Andrea Perez‐Silva
- School of Geography, Environment and Earth SciencesVictoria University of WellingtonWellingtonNew Zealand
| | | | - Martha Savage
- School of Geography, Environment and Earth SciencesVictoria University of WellingtonWellingtonNew Zealand
| | - Laura Wallace
- GNS ScienceLower HuttNew Zealand
- Institute for GeophysicsUniversity of Texas at AustinAustinTXUSA
| | - Duo Li
- Department of Earth and Environmental SciencesLudwig‐Maximilians‐Universität MünchenMünchenGermany
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Braden Z, Behr WM. Weakening Mechanisms in a Basalt-Hosted Subduction Megathrust Fault Segment, Southern Alaska. JOURNAL OF GEOPHYSICAL RESEARCH. SOLID EARTH 2021; 126:e2021JB022039. [PMID: 35865263 PMCID: PMC9285822 DOI: 10.1029/2021jb022039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/10/2021] [Revised: 08/20/2021] [Accepted: 08/26/2021] [Indexed: 06/15/2023]
Abstract
Basaltic and gabbroic rocks that define the seafloor have been suggested to act as sources of rheological heterogeneity during subduction, with the capacity to enhance or dampen seismicity. Despite this, relatively little is known from the rock record regarding the progression and conditions of mafic oceanic crust deformation during subduction, particularly in the shallow megathrust region of the seismogenic zone. We describe subduction-related deformation structures and characterize deformation conditions from an exhumed, basalt-hosted megathrust in the Chugach accretionary complex of south-central Alaska. Rocks in the Chugach preserve a record of seafloor mineralogical changes from pre-subduction, hydrothermal circulation that produced sheet silicates with a lower frictional strength than intact basalt. Pre-subduction alteration also served to introduce hydrous phases that can expel water during deformation and raise the pore fluid pressure. Once strain localized within basalts onto a megathrust fault plane at lithostatic pore fluid pressures, the basalt weakened further through a combination of cataclasis, dilatational shear fracturing, and slip on chlorite-rich shear bands. This process occurred in a narrower fault zone, and at higher maximum differential stress and greater pore fluid pressure fluctuations than recorded in some sediment-hosted megathrusts at similar pressure and temperature conditions. Our data indicate that when the lower plate contains basalt bathymetric features, basalt dismembers during subduction into a chlorite-rich fault gouge that surrounds lenses or slices of intact, less-altered basalt.
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Affiliation(s)
- Zoe Braden
- Department of Earth SciencesStructural Geology and Tectonics GroupGeological InstituteETH ZurichZurichSwitzerland
| | - Whitney M. Behr
- Department of Earth SciencesStructural Geology and Tectonics GroupGeological InstituteETH ZurichZurichSwitzerland
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Chesley C, Naif S, Key K, Bassett D. Fluid-rich subducting topography generates anomalous forearc porosity. Nature 2021; 595:255-260. [PMID: 34234336 DOI: 10.1038/s41586-021-03619-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Accepted: 05/07/2021] [Indexed: 02/06/2023]
Abstract
The role of subducting topography on the mode of fault slip-particularly whether it hinders or facilitates large megathrust earthquakes-remains a controversial topic in subduction dynamics1-5. Models have illustrated the potential for subducting topography to severely alter the structure, stress state and mechanics of subduction zones4,6; however, direct geophysical imaging of the complex fracture networks proposed and the hydrology of both the subducting topography and the associated upper plate damage zones remains elusive. Here we use passive and controlled-source seafloor electromagnetic data collected at the northern Hikurangi Margin, New Zealand, to constrain electrical resistivity in a region of active seamount subduction. We show that a seamount on the incoming plate contains a thin, low-porosity basaltic cap that traps a conductive matrix of porous volcaniclastics and altered material over a resistive core, which allows 3.2 to 4.7 times more water to subduct, compared with normal, unfaulted oceanic lithosphere. In the forearc, we image a sediment-starved plate interface above a subducting seamount with similar electrical structure to the incoming plate seamount. A sharp resistive peak within the subducting seamount lies directly beneath a prominent upper plate conductive anomaly. The coincidence of this upper plate anomaly with the location of burst-type repeating earthquakes and seismicity associated with a recent slow slip event7 directly links subducting topography to the creation of fluid-rich damage zones in the forearc that alter the effective normal stress at the plate interface by modulating the fluid overpressure. In addition to severely modifying the structure and physical conditions of the upper plate, subducting seamounts represent an underappreciated mechanism for transporting a considerable flux of water to the forearc and deeper mantle.
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Affiliation(s)
- Christine Chesley
- Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA.
| | - Samer Naif
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
| | - Kerry Key
- Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA
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Aretusini S, Meneghini F, Spagnuolo E, Harbord CW, Di Toro G. Fluid pressurisation and earthquake propagation in the Hikurangi subduction zone. Nat Commun 2021; 12:2481. [PMID: 33931641 PMCID: PMC8087711 DOI: 10.1038/s41467-021-22805-w] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Accepted: 03/31/2021] [Indexed: 02/02/2023] Open
Abstract
In subduction zones, seismic slip at shallow crustal depths can lead to the generation of tsunamis. Large slip displacements during tsunamogenic earthquakes are attributed to the low coseismic shear strength of the fluid-saturated and non-lithified clay-rich fault rocks. However, because of experimental challenges in confining these materials, the physical processes responsible for the coseismic reduction in fault shear strength are poorly understood. Using a novel experimental setup, we measured pore fluid pressure during simulated seismic slip in clay-rich materials sampled from the deep oceanic drilling of the Pāpaku thrust (Hikurangi subduction zone, New Zealand). Here, we show that at seismic velocity, shear-induced dilatancy is followed by pressurisation of fluids. The thermal and mechanical pressurisation of fluids, enhanced by the low permeability of the fault, reduces the energy required to propagate earthquake rupture. We suggest that fluid-saturated clay-rich sediments, occurring at shallow depth in subduction zones, can promote earthquake rupture propagation and slip because of their low permeability and tendency to pressurise when sheared at seismic slip velocities.
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Affiliation(s)
- S. Aretusini
- grid.410348.a0000 0001 2300 5064HPHT Laboratory, INGV, Rome, Italy
| | - F. Meneghini
- grid.5395.a0000 0004 1757 3729Department of Earth Sciences, University of Pisa, Pisa, Italy
| | - E. Spagnuolo
- grid.410348.a0000 0001 2300 5064HPHT Laboratory, INGV, Rome, Italy
| | - C. W. Harbord
- grid.83440.3b0000000121901201Department of Earth Sciences, University College London, London, UK
| | - G. Di Toro
- grid.410348.a0000 0001 2300 5064HPHT Laboratory, INGV, Rome, Italy ,grid.5608.b0000 0004 1757 3470Dipartimento di Geoscienze, University of Padua, Padua, Italy
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Copley A, Weller O, Cawood P, Warren C. Understanding earthquakes using the geological record: an introduction. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2021; 379:20190410. [PMID: 33517871 PMCID: PMC7898125 DOI: 10.1098/rsta.2019.0410] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 12/15/2020] [Indexed: 05/26/2023]
Affiliation(s)
- Alex Copley
- COMET, Department of Earth Sciences, University of Cambridge, Cambridge, UK
| | - Owen Weller
- Department of Earth Sciences, University of Cambridge, Cambridge, UK
| | - Peter Cawood
- School of Earth Atmosphere and Environment, Monash University, Melbourne, Australia
| | - Clare Warren
- School of Environment, Earth and Ecosystem Sciences, The Open University, Milton Keynes, UK
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Fagereng Å, Beall A. Is complex fault zone behaviour a reflection of rheological heterogeneity? PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2021; 379:20190421. [PMID: 33517872 PMCID: PMC7898124 DOI: 10.1098/rsta.2019.0421] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 08/18/2020] [Indexed: 05/26/2023]
Abstract
Fault slip speeds range from steady plate boundary creep through to earthquake slip. Geological descriptions of faults range from localized displacement on one or more discrete planes, through to distributed shearing flow in tabular zones of finite thickness, indicating a large range of possible strain rates in natural faults. We review geological observations and analyse numerical models of two-phase shear zones to discuss the degree and distribution of fault zone heterogeneity and effects on active fault slip style. There must be certain conditions that produce earthquakes, creep and slip at intermediate velocities. Because intermediate slip styles occur over large ranges in temperature, the controlling conditions must be effects of fault properties and/or other dynamic variables. We suggest that the ratio of bulk driving stress to frictional yield strength, and viscosity contrasts within the fault zone, are critical factors. While earthquake nucleation requires the frictional yield to be reached, steady viscous flow requires conditions far from the frictional yield. Intermediate slip speeds may arise when driving stress is sufficient to nucleate local frictional failure by stress amplification, or local frictional yield is lowered by fluid pressure, but such failure is spatially limited by surrounding shear zone stress heterogeneity. This article is part of a discussion meeting issue 'Understanding earthquakes using the geological record'.
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