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Seismic velocity models provide important constraints on Greenland's deep structure, which, in turn, has profound implications for our understanding of the tectonic history of this region. However, the resolution of seismic models has been limited by a sparse network, particularly in northern and central Greenland. We address these limitations by generating new high-resolution Rayleigh-wave phase velocity maps encompassing Greenland and northeastern Canada by processing over three decades of teleseismic earthquake records and incorporating recently added stations in Greenland and Arctic Canada. These phase velocity maps are sensitive to structure from the lower crust down to the sub-lithospheric mantle (25–185 s period). We find significant heterogeneity and a strong correlation between isotropic and anisotropic seismic velocities with inferred geological structure. High seismic velocities associated with cratonic lithosphere are broadly divided into two regions, with a belt of reduced velocity spanning central Greenland, which we interpret as lithospheric erosion resulting from interaction between the Greenland continental keel and the Iceland plume. Within each region, we identify tectonic subdivisions that suggest fundamental differences between the blocks that make up Precambrian Greenland. In the south, the North Atlantic craton (NAC) has a high-velocity keel exhibiting anisotropic stratification. Between the NAC and the cratonic lithosphere further north, the Proterozoic Nagssugtoqidian orogenic belt shows a distinct signature of reduced seismic velocity to |$\sim$| 75 s period, but then appears to pinch out at depth. The northern Greenland lithosphere exhibits significant isotropic heterogeneity, with a distinct core of high velocities in the northwest (⁠|$\sim$| 55–75 s period) giving way to a set of distinct east-west trending high-velocity belts at longer periods. At all periods sensitive to the lithospheric mantle in this region, anisotropic fast orientations are E–W, consistent with a north–south Precambrian assembly of the Greenland shield. In contrast to the NAC, there is no evidence of anisotropic stratification in the northern part of the cratonic keel. Based on both isotropic and anisotropic phase-velocity anomalies, we suggest that the Phanerozoic Caledonian and Ellesmerian-Franklinian fold belts are relatively thin-skinned features onshore Greenland, though the Caledonian belt may have a stronger signature off the east coast. At the longest periods, a prominent low-velocity anomaly initially centred on Iceland migrates northwards and spreads beneath central-eastern Greenland. Coupled with NW–SE trending anisotropy, this feature is interpreted as the effect of mantle flow radiating outward from the Iceland plume and interacting with the eroded Greenland lithosphere. [ABSTRACT FROM AUTHOR]

The Archean Superior craton was formed by the assemblage of continental and oceanic terranes at ∼2.6 Ga. The craton is surrounded by multiple Proterozoic mobile belts, including the Paleoproterozoic Trans‐Hudson Orogen which brought together the Superior and Rae/Hearne cratons at ∼1.9–1.8 Ga. Despite numerous studies on Precambrian lithospheric formation and evolution, the deep thermochemical structure of the Superior craton and its surroundings remains poorly understood. Here we investigate the upper mantle beneath the region from the surface to 400 km depth by jointly inverting Rayleigh wave phase velocity dispersion data, elevation, geoid height and surface heat flow, using a probabilistic inversion to obtain a (pseudo‐)3D model of composition, density and temperature. The lithospheric structure is dominated by thick cratonic roots (>300 km) beneath the eastern and western arms of the Superior craton, with a chemically depleted signature (Mg# > 92.5), consistent with independent results from mantle xenoliths. Beneath the surrounding Proterozoic and Phanerozoic orogens, the Mid‐continent Rift and Hudson Strait, we observe a relatively thinner lithosphere and more fertile composition, indicating that these regions have undergone lithospheric modification and erosion. Our model supports the hypothesis that the core of the Superior craton is well‐preserved and has evaded lithospheric destruction and refertilization. We propose three factors playing a critical role in the craton's stability: (a) the presence of a mid‐lithospheric discontinuity, (b) the correct isopycnic conditions to sustain a strength contrast between the craton and the surrounding mantle, and (c) the presence of weaker mobile belts around the craton. Plain Language Summary: We introduce a new model of the temperature and composition of the Superior Craton, a stable and ancient (>2.5 billion years old) geological formation, and its neighboring areas, by using an advanced and novel imaging technique. The central aim of the study is to use the present‐day structure (from the surface to 400 km depth) to understand how the craton's lithosphere (the rigid outer layer of the Earth) has evolved over time, and how its deep roots have persisted over billions of years of geological processes. The Superior Craton displays well‐preserved cores with a distinct chemical composition beneath its eastern and western arms, which likely contribute to its long‐term preservation. Isopycnicity (a state of density equilibrium) within the lithosphere is a likely controller of long‐term stability. Additionally, the presence of layering in the lithosphere and weaker structures (e.g., mountain belts, rifts, hotspot tracks) surrounding the edges of the craton emerge as critical factors contributing to the resilience and endurance of the Superior Craton's lithosphere. These findings significantly advance our understanding of the mechanisms governing the evolution and stability of cratonic regions. Key Points: First integrated multi‐observable probabilistic thermochemical model of the lithosphere beneath the Superior craton and environsThe Superior craton shows well‐preserved depleted cores beneath its eastern and western armsLong‐term craton stability is likely controlled by isopycnicity, and the presence of mid‐lithospheric discontinuities and mobile belts [ABSTRACT FROM AUTHOR]

Two-station surface-wave analysis was used to measure Rayleigh-wave phase velocities between 105 station pairs in western Canada, straddling the boundary between the tectonically active Cordillera and the adjacent stable craton. Major variations in phase velocity are seen across the boundary at periods from 15 to 200 s, periods primarily sensitive to upper mantle structure. Tomographic inversion of these phase velocities was used to generate phase velocity maps at these periods, indicating a sharp contrast between low-velocity Cordilleran upper mantle and high-velocity cratonic lithosphere. Depth inversion along selected transects indicates that the Cordillera-craton upper mantle contact varies in dip along the deformation front, with cratonic lithosphere of the Taltson province overthrusting Cordilleran asthenosphere in the northern Cordillera, and Cordilleran asthenosphere overthrusting Wopmay lithosphere further south. Localized high-velocity features at sublithospheric depths beneath the Cordillera are interpreted as Farallon slab fragments, with the gap between these features indicating a slab window. A high-velocity feature in the lower lithosphere of the Slave province may be related to Proterozic or Archean subduction. Key words: seismology, surface waves, tomography, Cordillera, craton. L'analyse des ondes de surface entre deux stations a ete utilisee pour mesurer les vitesses de phase des ondes de Rayleigh entre 105 paires de stations dans l'Ouest canadien enjambant la frontiere entre la Cordillere, une zone tectoniquement active, et le craton stable attenant. D'importantes variations des vitesses de phase sont observees de part et d'autre de la frontiere a des periodes allant de 15 a 200 s, ces periodes etant principalement sensibles a la structure du manteau superieur. L'inversion tomographique de ces vitesses de phase a ete utilisee pour produire des cartes de vitesses de phase a ces periodes, qui montrent un contraste marque entre le les basses vitesses du manteau superieur de la Cordillere et les hautes vitesses de la lithosphere cratonique. L'inversion de la profondeur le long de differentes coupes sismiques indique que le pendage du contact des manteaux superieurs de la Cordillere et du craton varie le long du front de deformation, la lithosphere cratonique de la province de Talston chevauchant l'asthenosphere de la Cordillere au nord, et l'asthenosphere de la Cordillere chevauchant la lithosphere de l'orogene de Wopmay plus au sud. Des elements localises de haute vitesse a des profondeurs sub-lithospheriques sous la Cordillere sont interpretes comme etant des fragments de la plaque de Farallon, l'intervalle entre ces elements indiquant la presence d'une fenetre asthenospherique. Un element de haute vitesse dans la lithosphere inferieure de la province des Esclaves pourrait etre relie a une subduction proterozoique ou archeenne. [Traduit par la Redaction] Mots-cles : sismologie, ondes de surface, tomographie, Cordillere, craton., Introduction The lithosphere beneath stable continental regions typically exhibits elevated seismic velocities to depths of 200 km or more, which has been attributed to a combination of low temperature and [...]

Ambient seismic noise is mainly generated in oceans through the interactions between the atmosphere, ocean waves and the solid Earth. Study areas located near the edges of continents are thus subject to receiving an inhomogeneous noise field that could cause bias in ambient noise wave attenuation measurements and tomography studies. Ambient seismic noise characteristics across SE Canada and the NE USA are studied in detail at a regional scale for the first time, due to the availability of over 2 yr of data (2013–2015) recorded at 69 broad-band seismographs. This large, dense data set allowed us to use a back-projection technique to investigate both the azimuthal and temporal variations of the ambient noise. This method is based on a statistical analysis of signal-to-noise ratios (SNRs) of the waveforms in the calculated empirical Green's functions for pairs of stations. We propose a new method of analysing the SNR by modifying the already existing concept of fan diagrams to include both causal and acausal components of the noise cross-correlograms in the analysis. We investigate directional and seasonal variations of the recorded noise data across the study area at the three main passbands of the seismic noise spectrum including the secondary microseisms (SM; 3–10 s), the primary microseisms (PM; 10–30 s), and the seismic hum (Hum; 30–300 s). We observe that the strongest and weakest signals are received at the SM and Hum bands, respectively. Considering the results of this study along with those from previous studies, we conclude that the strongest seismic noise arrivals at the three passbands investigated in this study (i.e. SM, PM and Hum) are generated at different locations in the Atlantic, Pacific and Arctic oceans. [ABSTRACT FROM AUTHOR]

Surface wave tomography is a valuable tool for constraining azimuthal anisotropy at regional scales. However, sparse and uneven coverage of dispersion measurements make meaningful uncertainty estimation challenging, especially when applying subjective model regularization. This paper considers azimuthal anisotropy constrained by measurements of surface wave dispersion data within a Bayesian trans-dimensional (trans-d) tomographic inversion. A recently proposed alternative model parametrization for trans-d inversion is implemented in order to produce more realistic models than previous studies considering trans-d surface wave tomography. The reversible-jump Markov chain Monte Carlo sampling technique is used to numerically estimate the posterior probability density of the model parameters. Isotropic and azimuthally anisotropic components of surface wave group velocity maps (and their associated uncertainties) are estimated while avoiding model regularization and allowing model complexity to be determined by the data information content. Furthermore, data errors are treated as unknown, and solved for within the inversion. The inversion method is applied to measurements of surface wave dispersion from regional earthquakes recorded over northern Cascadia and Haida Gwaii, a region of complex active tectonics but highly heterogeneous station coverage. Results for isotropic group velocity are consistent with previous studies that considered the southern part of the study region over Cascadia. Azimuthal anisotropic fast-axis directions are generally margin-parallel between Vancouver Island and Haida Gwaii, with a small change in direction and magnitude along the margin which may be attributed to the changing tectonic regime (from subduction to transform tectonics). Estimated errors on the dispersion data (solved for within the inversion) reveal a correlation between surface wave period and the dependence of data errors on travel path length. This paper demonstrates the value of considering azimuthal anisotropy within Bayesian tomographic inversions. Furthermore, this work provides structural context for future studies of tectonic structure and dynamics of northern Cascadia and Haida Gwaii, with the aim of improving our understanding of seismic and tsunami hazards. [ABSTRACT FROM AUTHOR]