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Cascadia low frequency earthquakes at the base of an overpressured subduction shear zone. Nat Commun 2020; 11:3874. [PMID: 32747641 PMCID: PMC7398906 DOI: 10.1038/s41467-020-17609-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Accepted: 07/08/2020] [Indexed: 12/05/2022] Open
Abstract
In subduction zones, landward dipping regions of low shear wave velocity and elevated Poisson’s ratio, which can extend to at least 120 km depth, are interpreted to be all or part of the subducting igneous oceanic crust. This crust is considered to be overpressured, because fluids within it are trapped beneath an impermeable seal along the overlying inter-plate boundary. Here we show that during slow slip on the plate boundary beneath southern Vancouver Island, low frequency earthquakes occur immediately below both the landward dipping region of high Poisson’s ratio and a 6–10 km thick shear zone revealed by seismic reflections. The plate boundary here either corresponds to the low frequency earthquakes or to the anomalous elastic properties in the lower 3–5 km of the shear zone immediately above them. This zone of high Poisson’s ratio, which approximately coincides with an electrically conductive layer, can be explained by slab-derived fluids trapped at near-lithostatic pore pressures. Regions of the subducting oceanic crust are often considered to be overpressured, owing to fluid trapped beneath an impermeable seal along the overlying inter-plate boundary. Here, the authors show that slow slip earthquakes at the Cascadia subduction zone occur immediately below a 6-10 km-thick shear zone, in which slab-derived fluids are likely trapped at near-lithostatic pore pressures.
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Chevrot S, Sylvander M, Diaz J, Martin R, Mouthereau F, Manatschal G, Masini E, Calassou S, Grimaud F, Pauchet H, Ruiz M. The non-cylindrical crustal architecture of the Pyrenees. Sci Rep 2018; 8:9591. [PMID: 29941925 PMCID: PMC6018422 DOI: 10.1038/s41598-018-27889-x] [Citation(s) in RCA: 61] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Accepted: 06/08/2018] [Indexed: 11/09/2022] Open
Abstract
We exploit the data from five seismic transects deployed across the Pyrenees to characterize the deep architecture of this collisional orogen. We map the main seismic interfaces beneath each transect by depth migration of P-to-S converted phases. The migrated sections, combined with the results of recent tomographic studies and with maps of Bouguer and isostatic anomalies, provide a coherent crustal-scale picture of the belt. In the Western Pyrenees, beneath the North Pyrenean Zone, a continuous band of high density/velocity material is found at a very shallow level (~10 km) beneath the Mauleon basin and near Saint-Gaudens. In the Western Pyrenees, we also find evidence for northward continental subduction of Iberian crust, down to 50-70 km depth. In the Eastern Pyrenees, these main structural features are not observed. The boundary between these two domains is near longitude 1.3 °E, where geological field studies document a major change in the structure of the Cretaceous rift system, and possibly a shift of its polarity, suggesting that the deep orogenic architecture of the Pyrenees is largely controlled by structural inheritance.
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Affiliation(s)
| | | | - Jordi Diaz
- Institute of Earth Sciences Jaume Almeria, ICTJA-CSIC, Barcelona, Spain
| | - Roland Martin
- GET, Université de Toulouse, CNRS, IRD, UPS, Toulouse, France
| | | | | | | | | | - Frank Grimaud
- IRAP, Université de Toulouse, CNRS, CNES, UPS, Toulouse, France
| | - Hélène Pauchet
- IRAP, Université de Toulouse, CNRS, CNES, UPS, Toulouse, France
| | - Mario Ruiz
- Institute of Earth Sciences Jaume Almeria, ICTJA-CSIC, Barcelona, Spain
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Yue H, Chen YJ, Sandvol E, Ni J, Hearn T, Zhou S, Feng Y, Ge Z, Trujillo A, Wang Y, Jin G, Jiang M, Tang Y, Liang X, Wei S, Wang H, Fan W, Liu Z. Lithospheric and upper mantle structure of the northeastern Tibetan Plateau. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2011jb008545] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Kim Y, Clayton RW, Jackson JM. Geometry and seismic properties of the subducting Cocos plate in central Mexico. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009jb006942] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Affiliation(s)
- Bruce A Buffett
- Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA.
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Rossi G, Abers GA, Rondenay S, Christensen DH. Unusual mantle Poisson's ratio, subduction, and crustal structure in central Alaska. ACTA ACUST UNITED AC 2006. [DOI: 10.1029/2005jb003956] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Park J, Yuan H, Levin V. Subduction zone anisotropy beneath Corvallis, Oregon: A serpentinite skid mark of trench-parallel terrane migration? ACTA ACUST UNITED AC 2004. [DOI: 10.1029/2003jb002718] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Jeffrey Park
- Department of Geology and Geophysics; Yale University; New Haven Connecticut USA
| | - Huaiyu Yuan
- Department of Geology and Geophysics; Yale University; New Haven Connecticut USA
| | - Vadim Levin
- Department of Geology and Geophysics; Yale University; New Haven Connecticut USA
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Bostock MG, Hyndman RD, Rondenay S, Peacock SM. An inverted continental Moho and serpentinization of the forearc mantle. Nature 2002; 417:536-8. [PMID: 12037564 DOI: 10.1038/417536a] [Citation(s) in RCA: 485] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge, resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere. Asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back-arc region, but the forearc mantle (in the corner of the wedge) is thought to be significantly cooler. Here we explore the structure of the mantle wedge in the southern Cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers. We find very low shear-wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an 'inverted' continental Moho, which reverts to normal polarity seaward of the Cascade arc. This observation provides compelling evidence for a highly hydrated and serpentinized forearc region, consistent with thermal and petrological models of the forearc mantle wedge. This serpentinized material is thought to have low strength and may therefore control the down-dip rupture limit of great thrust earthquakes, as well as the nature of large-scale flow in the mantle wedge.
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Affiliation(s)
- M G Bostock
- Department of Earth and Ocean Sciences, The University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
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Rondenay S, Bostock MG, Shragge J. Multiparameter two-dimensional inversion of scattered teleseismic body waves 3. Application to the Cascadia 1993 data set. ACTA ACUST UNITED AC 2001. [DOI: 10.1029/2000jb000039] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Shragge J, Bostock MG, Rondenay S. Multiparameter two-dimensional inversion of scattered teleseismic body waves 2. Numerical examples. ACTA ACUST UNITED AC 2001. [DOI: 10.1029/2001jb000326] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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