The ArcCRUST model consists of crustal thickness and estimated crustal thinning factors grids for the High Arctic and Circum‐Arctic regions (north of 67^oN). This model is derived by using 3D forward and inverse gravity modelling. Updated sedimentary thickness grid, an oceanic lithosphere age model together with inferred microcontinent rifting ages, variable crystalline crust and sediment densities, and dynamic topography models constrain this inversion. We use published high‐quality 2D seismic crustal‐scale models to create a database of Depths to Seismic Moho (DSM) profiles. To check the quality of the ArcCRUST model, we have performed a statistical analysis of misfits between the ArcCRUST Moho depths and DSM values. Systematic analysis of the misfits within the Arctic sedimentary basins provides information about tectonic processes unaccounted by the assumed model of pure‐shear lithospheric extension. In particular, our model implies a less‐dense and/or thin mantle lithosphere underneath microcontinents in the deep Arctic Ocean where the ArcCRUST depth to Moho values exceed the depth to seismic Moho. A systematically larger gravity‐derived crustal thickness (ca. 3 km) under the western and northern Greenland Sea points to a hotter upper mantle implied by the seismic tomography models in the North Atlantic.

Microseismicity is often assumed to be directly linked to the pore pressure increase by shifting stress conditions onto the Mohr-Coulomb yield surface. In addition, a large proportion of seismic events occurs mainly within the reservoir and have tensile opening component, characteristic of fluid-filled fractures. However, there are observations of injection-induced microseismicity at large offset distances from the operation site. Such seismic events often occur at some distance from the reservoir or pressure front and are characterized by mainly double couple source mechanism. We discuss mechanisms that might trigger such events and show that in deformable porous rocks stress changes and subsequent induced seismicity might happen ahead of the fluid pressure diffusion front. Localization of the fluid flow that might occur in rocks exhibiting time-dependent creep, e.g. shales, might lead to out-of-zone seismicity that continues even after injection has been stopped.

Long‐period magnetotelluric (MT) data can be used to interpret upper mantle temperature, hydrogen content, and the presence of partial melt, all of which strongly influence mantle viscosity. We have collected the first long‐period MT data in Svalbard and have combined them with preexisting broadband MT data to produce a model of the electrical resistivity of Svalbard's upper mantle. Asthenospheric resistivities are low compared to stable continental settings but more comparable to young oceanic asthenosphere, suggesting that the physical state of Svalbard's upper mantle is controlled by its proximity to the Mid‐Atlantic Ridge. Interpretation of the MT model using a petrologically constrained genetic algorithm approach shows that partial melt is present in the uppermost asthenosphere beneath Svalbard. This is the first direct evidence of partial melt in Svalbard's asthenosphere from deep geophysical soundings. Viscosities calculated from the geophysical data show a low viscosity layer (~10¹⁸ Pa s) coincident with the partial melt layer, underlain by a higher viscosity layer (~10²⁰ Pa s) extending to the transition zone. Viscosities calculated from glacial isostatic adjustment (GIA) data in Svalbard show a considerable range due mainly to uncertainties in past ice sheet models. Improved constraints on Svalbard's mantle viscosity from geophysical data may help to improve these GIA models.

Late Cretaceous‐Cenozoic contractional structures are widespread in the Barents Sea. While the exact dating of the deformation is unclear, it can only be inferred that the contraction is younger than the early Cretaceous. One likely contractional mechanism is related to Greenland Plate kinematics at Paleogene times. We use a thin sheet finite element modeling approach to compute deformation within the Barents Sea in response to the Greenland‐Eurasia relative motions during the Paleogene. The analytical solution for the 3‐D folding of sediments above basement faults is used to assess possibilities for folding. Two existing Greenland Plate kinematic models, differing slightly in the timing, magnitude, and direction of motion, are tested. Results show that the Greenland Plate's general northward motion promotes growing anticlines in the entire Barents Sea shelf. Our numerical models suggest that the fan‐shaped pattern of cylindrical anticlines in the Barents Sea can be associated with the Eurekan deformation concurrent to the initial rifting and early seafloor spreading in the northeast Atlantic. The main contraction phase in the SW Barents Sea coincides with the timing of continental breakup, whereas the peak of deformation predicted for the NW Barents Sea occurred at later times. Svalbard has experienced a prolonged period of compressional deformation. We conclude that Paleogene Greenland Plate kinematics are a likely candidate to explain contractional structures in the Barents Sea.

SUMMARY: The microseismic events can often be characterized by a complex non-double couple source mechanism. Recent laboratory studies recording the acoustic emission during rock deformation help connecting the components of the seismic moment tensor with the failure process. In this complementary contribution, we offer a mathematical model which can further clarify these connections. We derive the seismic moment tensor based on classical continuum mechanics and plasticity theory. The moment tensor density can be represented by the product of elastic stiffness tensor and the plastic strain tensor. This representation of seismic sources has several useful properties: (i) it accounts for incipient faulting as a microseismicity source mechanism, (ii) it does not require a pre-defined fracture geometry, (iii) it accounts for both shear and volumetric source mechanisms, (iv) it is valid for general heterogeneous and anisotropic rocks and (v) it is consistent with elasto-plastic geomechanical simulators. We illustrate the new approach using 2-D numerical examples of seismicity associated with cylindrical openings, analogous to wellbore, tunnel or fluid-rich conduit and provide a simple analytic expression of the moment density tensor. We compare our simulation results with previously published data from laboratory and field experiments. We consider four special cases corresponding to ‘dry’ elastically homogeneous and elastically heterogeneous isotropic rocks, ‘dry’ transversely isotropic rocks and ‘wet’ isotropic rocks. The model highlights theoretical links between stress state, geomechanical parameters and conventional representations of the moment tensor such as Hudson source type parameters.

The seismic oceanography method is based on extracting and stacking the low-frequency acoustic energy scattered by the ocean heterogeneity. However, a good understanding on how this acoustic wavefield is affected by physical processes in the ocean is still lacking. In this work an acoustic waveform modeling and inversion method is developed and applied to both synthetic and real data. In the synthetic example, the temperature field is simulated as a homogeneous Gaussian isotropic random field with the Kolmogorov–Obukhov spectrum superimposed on a background stratified ocean structure. The presented full waveform inversion method is based on the ray-Born approximation. The synthetic seismograms computed using the ray-Born scattering method closely match the seismograms produced with a more computationally expensive finite-difference method. The efficient solution to the inverse problem is provided by the multiscale nonlinear inversion approach that is specifically stable with respect to noise. Full waveform inversion tests are performed using both the stationary and time-dependent sound speed models. These tests show that the method provides a reliable reconstruction of both the spatial sound speed variation and the theoretical spectrum due to fully developed turbulence. Finally, the inversion approach is applied to real seismic reflection data to determine the heterogeneous sound speed structure at the west Barents Sea continental margin in the northeast Atlantic. The obtained model illustrates in more detail the processes of diapycnal mixing near the continental slope.