Tomographic imaging of the Cascadia subduction zone: Constraints on the Juan de Fuca slab

Chen, Chuanxu; Zhao, Dapeng; Wu, Shiguo

doi:10.1016/j.tecto.2015.02.012

Cited by 36 publications

(24 citation statements)

References 70 publications

(87 reference statements)

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“…We attribute differences in our results to key differences in our methodology, specifically our use of a detailed 3‐D starting model (including elevation) rather than station statics to account for shallow structure and our iterative 3‐D ray tracing approach to solving the forward problem. Chen et al () image localized low‐velocity anomalies consistent with our results, postulating they may be regions of mantle upwelling but lack the offshore constraints to explore their potential origins as we do here (see section 4.1).…”

Section: Tomographic Resultssupporting

confidence: 86%

Buoyant Asthenosphere Beneath Cascadia Influences Megathrust Segmentation

Bodmer

Toomey

Hooft

et al. 2018

Geophysical Research Letters

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Great megathrust earthquakes (magnitude 8+) do not typically rupture an entire convergent margin but rather are limited to one or more along‐strike segments. A fundamental question of subduction zone dynamics and hazard assessment is what physical properties or dynamic processes govern megathrust segmentation. Here we use onshore‐offshore teleseismic delay time data to tomographically image the upper mantle seismic structure of the Cascadia subduction zone. Our results reveal along‐strike segmentation in the oceanic asthenosphere beneath the subducting plate with pronounced low‐velocity anomalies below regions of increased plate locking and greater occurrence of episodic tremor and slip. We attribute the anomalous asthenospheric velocities to independent mantle upwellings associated with hot spot‐derived material in northern Cascadia and fragmentation processes at a diffuse plate boundary in southern Cascadia. Based on these relations, we hypothesize that subslab buoyancy modulates the plate coupling force at the thrust interface, thereby contributing to the localization of subduction zone segmentation.

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Section: Tomographic Resultssupporting

confidence: 86%

Buoyant Asthenosphere Beneath Cascadia Influences Megathrust Segmentation

Bodmer

Toomey

Hooft

et al. 2018

Geophysical Research Letters

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“…Previous tomographic results suggest that low‐ V anomalies in the lower crust and upper mantle may reflect the existence of fluids (melt or water) [e.g., Zhao et al , , , ; Liu et al , , ; Tian and Zhao , ; Wei et al , ; Chen et al , , ; Liu and Zhao , ]. Electrical resistivity results show that high‐conductivity zones exist in the lower crust under the Qilian Orogenic Belt and Western Qinling, though they are distributed intermittently in some local areas, indicating the existence of water in the lower crust [ Tang et al , ; Zhao et al , ].…”

Section: Interpretation and Discussionmentioning

confidence: 99%

“…As discussed in section 4.2, the low‐ V p , low‐ σ , and high‐conductivity anomalies [ Tang et al , ; Zhao et al , ] in the lower crust indicate the existence of water which results from dehydration of hydrous minerals in the deeper crust and uppermost mantle and can weaken the lower crust beneath the northeastern corner of the Tibetan Plateau. Similar high‐conductivity and low‐ V anomalies have been revealed in the source areas of large crustal earthquakes in other regions [e.g., Zhao et al , , ; Mishra and Zhao , ; Lei and Zhao , ; Cheng et al , ; Tong et al , ; Wei et al , ; Chen et al , , ]. However, in the northeastern margin of the Qilian Orogenic Belt where several large fault zones are distributed, obvious low‐ V s and high‐ σ anomalies exist in the lower crust beneath six large crustal earthquakes, which could extend down to the uppermost mantle (Figures d, b, c, and a).…”

Section: Interpretation and Discussionmentioning

confidence: 99%

Seismic tomography and anisotropy of the Helan‐Liupan tectonic belt: Insight into lower crustal flow and seismotectonics

et al. 2016

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We determined detailed 3‐D P and S wave velocities (Vp and Vs) and Poisson's ratio (σ) images as well as P wave azimuthal anisotropy in the crust and uppermost mantle beneath the Helan‐Liupan tectonic belt (HLTB) and adjacent regions. The data set used in this study consists of 38,880 P wave and 35,117 S wave arrival times from 5028 local earthquakes recorded by 66 seismic stations in the study area during 1980 to 2014. Obvious low‐Vp and low‐σ anomalies are revealed in the lower crust beneath the Qilian Orogenic Belt and Western Qinling, which we interpret as a weakened zone mainly caused by water and capable of ductile flow on a geological timescale. Our P wave anisotropy results suggest that the flow direction in the lower crust is nearly parallel to the direction of the geodetic crustal motion and that of the upper mantle flow beneath the study region. Most of the 26 large historical earthquakes (1125–1954) in the study region occurred in the boundary zones where Vp, Vs, and σ change drastically over a short distance. Beneath the source areas of the large historical earthquakes, fluid‐related low‐velocity zones exist widely in the lower crust. The fluids result from dehydration of hydrous minerals in the deeper crust and uppermost mantle beneath the northeastern Tibetan Plateau. When the fluids migrate upward to the active faults, the fault zone friction is reduced and so large crustal earthquakes can be triggered. Our present results shed new light on the seismogenesis and geodynamics of the northeastern Tibetan Plateau and adjacent areas.

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“…Many high-resolution seismic images have been obtained and we are beginning to narrow down the mantle structure, particularly beneath the western US, to the scale of~200 km (e.g., Becker, 2012;Chen et al, 2014Chen et al, , 2015. The tectonic involution of western US, including the active subduction of the Juan der Fuca plate, extensive subduction-related volcanism and intraplate volcanism (e.g., the Yellowstone hotspot), as well as mountain building, was thoroughly discussed and many models have been proposed on the basis of slab-mantle interactions revealed by the seismic images (e.g., Becker, 2012;Tian and Zhao, 2012b;Chen et al, 2015). The dark red area shows an anomaly with an extremely strong amplitude.…”

Section: North Americamentioning

confidence: 99%

Seismic anisotropy tomography: New insight into subduction dynamics

2016

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Body-wave and surface-wave tomography, receiver-function imaging, and shear-wave splitting measurements have shown that seismic anisotropy and heterogeneity coexist in all parts of subduction zones, providing important constraints on the mantle flow and subduction dynamics. P-wave anisotropy tomography is a new but powerful tool for mapping three-dimensional variations of azimuthal and radial seismic anisotropy in the crust and mantle. P-wave azimuthal-anisotropy tomography has been applied widely to the Circum-Pacific subduction zones, Mainland China and North America, whereas P-wave radial-anisotropy tomography was applied to only a few areas including Northeast Japan, Southwest Japan and North China Craton. These studies have revealed complex anisotropy in the crust and mantle lithosphere associated with the surface geology and tectonics, anisotropy reflecting subduction-driven corner flow in the mantle wedge, frozen-in fossil anisotropy in the subducting slabs formed at the mid-ocean ridge, as well as olivine fabric transitions due to changes in water content, stress and temperature. Shear-wave splitting tomography methods have been also proposed, but their applications are still limited and preliminary. There is a discrepancy between the surface-wave and body-wave tomographic models in radial anisotropy of the mantle wedge beneath Japan, which is a puzzle but an intriguing topic for future studies.

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Tomographic imaging of the Cascadia subduction zone: Constraints on the Juan de Fuca slab

Cited by 36 publications

References 70 publications

Buoyant Asthenosphere Beneath Cascadia Influences Megathrust Segmentation

Buoyant Asthenosphere Beneath Cascadia Influences Megathrust Segmentation

Seismic tomography and anisotropy of the Helan‐Liupan tectonic belt: Insight into lower crustal flow and seismotectonics

Seismic anisotropy tomography: New insight into subduction dynamics

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