Shane Detweiler

Bio: Shane Detweiler is an academic researcher from United States Geological Survey. The author has contributed to research in topics: Crust & Mantle (geology). The author has an hindex of 6, co-authored 6 publications receiving 337 citations.

A three‐dimensional geophysical model of the crust in the Barents Sea region: model construction and basement characterization

Abstract: SUMMARY BARENTS50, a new 3-D geophysical model of the crust in the Barents Sea Region has been developed by the University of Oslo, NORSAR and the U.S. Geological Survey. The target region comprises northern Norway and Finland, parts of the Kola Peninsula and the East European lowlands. Novaya Zemlya, the Kara Sea and Franz-Josef Land terminate the region to the east, while the Norwegian-Greenland Sea marks the western boundary. In total, 680 1-D seismic velocity profiles were compiled, mostly by sampling 2-D seismic velocity transects, from seismic refraction profiles. Seismic reflection data in the western Barents Sea were further used for density modelling and subsequent density-to-velocity conversion. Velocities from these profiles were binned into two sedimentary and three crystalline crustal layers. The first step of the compilation comprised the layer-wise interpolation of the velocities and thicknesses. Within the different geological provinces of the study region, linear relationships between the thickness of the sedimentary rocks and the thickness of the remaining crystalline crust are observed. We therefore, used the separately compiled (area-wide) sediment thickness data to adjust the total crystalline crustal thickness according to the total sedimentary thickness where no constraints from 1-D velocity profiles existed. The BARENTS50 model is based on an equidistant hexagonal grid with a node spacing of 50 km. The P-wave velocity model was used for gravity modelling to obtain 3-D density structure. A better fit to the observed gravity was achieved using a grid search algorithm which focussed on the density contrast of the sediment-basement interface. An improvement compared to older geophysical models is the high resolution of 50 km. Velocity transects through the 3-D model illustrate geological features of the European Arctic. The possible petrology of the crystalline basement in western and eastern Barents Sea is discussed on the basis of the observed seismic velocity structure. The BARENTS50 model is available at http://www.norsar.no/seismology/barents3d/.

Three-dimensional model for the crust and upper mantle in the Barents Sea region

Abstract: The Barents Sea and its surroundings is an epicontinental region which previously has been difficult to access, partly because of its remote Arctic location (Figure 1) and partly because the region has been politically sensitive. Now, however, this region, and in particular its western parts, has been very well surveyed with a variety of geophysical studies, motivated in part by exploration for hydrocarbon resources. Since this region is interesting geophysically as well as for seismic verification, a major study [Bungum et al., 2004] was initiated in 2003 to develop a three-dimensional (3-D) seismic velocity model for the crust and upper mantle, using a grid density of 50 km. This study, in cooperation between NORSAR, the University of Oslo (UiO),and the U.S.Geological Survey (USGS), has led to the construction of a higher-resolution, regional lithospheric model based on a comprehensive compilation of available seismological and geophysical data. Following the methodology employed in making the global crustal model CRUST5.1 [Mooney et al., 1998], the new model consists of five crustal layers: soft and hard sediments, and crystalline upper, middle, and lower crust. Both P- and S-wave velocities and densities are specified in each layer. In addition, the density and seismic velocity structure of the uppermost mantle, essential for Pn and Sn travel time modeling, are included.

Earth History and Palaeogeography

Abstract: Using full-colour palaeogeographical maps from the Cambrian to the present, this interdisciplinary volume explains how plate motions and surface volcanism are linked to processes in the Earth's mantle, and to climate change and the evolution of the Earth's biota. These new and very detailed maps provide a complete and integrated Phanerozoic story of palaeogeography. They illustrate the development of all the major mountain-building orogenies. Old lands, seas, ice caps, volcanic regions, reefs, and coal beds are highlighted on the maps, as well as faunal and floral provinces. Many other original diagrams show sections from the Earth's core, through the mantle, and up to the lithosphere, and how Large Igneous Provinces are generated, helping to understand how plates have appeared, moved, and vanished through time. Supplementary resources are available online, making this an invaluable reference for researchers, graduate students, professional geoscientists and anyone interested in the geological history of the Earth.

The Moho depth map of the European Plate

Abstract: SUMMARY The European Plate has a 4.5 Gy long and complex tectonic history. This is reflected in the present-day large-scale crustal structures. A new digital Moho depth map is compiled from more than 250 data sets of individual seismic profiles, 3-D models obtained by body and surface waves, receiver function results and maps of seismic and/or gravity data compilations. We have compiled the first digital, high-resolution map of the Moho depth for the whole European Plate, extending from the mid-Atlantic ridge in the west to the Ural Mountains in the east, and from the Mediterranean Sea in the south to the Barents Sea and Spitsbergen in the Arctic in the north. In general, three large domains within the European Plate crust are visible. The oldest Archean and Proterozoic crust has a thickness of 40–60 km, the continental Variscan and Alpine crust has a thickness of 20–40 km, and the youngest oceanic Atlantic crust has a thickness of 10–20 km.

Seismic tomography of the southern California crust based on spectral‐element and adjoint methods

Abstract: We iteratively improve a 3-D tomographic model of the southern California crust using numerical simulations of seismic wave propagation based on a spectral-element method (SEM) in combination with an adjoint method. The initial 3-D model is provided by the Southern California Earthquake Center. The data set comprises three-component seismic waveforms (i.e. both body and surface waves), filtered over the period range 2–30 s, from 143 local earthquakes recorded by a network of 203 stations. Time windows for measurements are automatically selected by the FLEXWIN algorithm. The misfit function in the tomographic inversion is based on frequency-dependent multitaper traveltime differences. The gradient of the misfit function and related finite-frequency sensitivity kernels for each earthquake are computed using an adjoint technique. The kernels are combined using a source subspace projection method to compute a model update at each iteration of a gradient-based minimization algorithm. The inversion involved 16 iterations, which required 6800 wavefield simulations. The new crustal model, m_(16), is described in terms of independent shear (V_S) and bulk-sound (V_B) wave speed variations. It exhibits strong heterogeneity, including local changes of ±30 per cent with respect to the initial 3-D model. The model reveals several features that relate to geological observations, such as sedimentary basins, exhumed batholiths, and contrasting lithologies across faults. The quality of the new model is validated by quantifying waveform misfits of full-length seismograms from 91 earthquakes that were not used in the tomographic inversion. The new model provides more accurate synthetic seismograms that will benefit seismic hazard assessment.

EPcrust: a reference crustal model for the European Plate

Abstract: SUMMARY We present a new crustal model for the European Plate, derived from collection and critical integration of information selected from the literature. The model covers the whole European Plate from North Africa to the North Pole (20 ◦ N–90 ◦ N) and from the Mid-Atlantic Ridge to the Urals (40 ◦ W–70 ◦ E). The chosen parametrization represents the crust in three layers (sediments, upper crust and lower crust), and describes the 3-D geometry of the interfaces and seismologically relevant parameters—isotropic P- and S-wave velocity, plus density—with a resolution of 0.5 ◦ × 0.5 ◦ on a geographical latitude–longitude grid. We selected global and local models, derived from geological assumptions, active seismic experiments, surface wave studies, noise correlation, receiver functions. Model EPcrust presents significant advantages with respect to previous models: it covers the whole European Plate; it is a complete and internally-consistent model (with all the parameters provided, also for the sedimentary layer); it is reproducible; it is easy to update in the future by adding new contributions; and it is available in a convenient digital format. EPcrust could be used to account for crustal structure in seismic wave propagation modelling at continental scale or to compute linearized crustal corrections in continental scale seismic tomography, gravity studies, dynamic topography and other applications that require a reliable crustal structure. Because of its resolution, our model is not suited for local-scale studies, such as the computation of earthquake scenarios, where more detailed knowledge of the structure is required. We plan to update the model as new data will become available, and possibly improve its resolution for selected areas in the future.

Testing models of Tibetan Plateau formation with Cenozoic shortening estimates across the Qilian Shan–Nan Shan thrust belt

Abstract: Competing models that account for the construction of the Tibetan Plateau include continental subduction, underthrusting, distributed shortening, channel flow, and older crustal-structure inheritance. Well-constrained estimates of crustal shortening strain serve as a diagnostic test of these plateau formation models and are critical to elucidate the dominant mechanism of plateau development. In this work we estimate the magnitude of Cenozoic shortening across the northern Qilian Shan–Nan Shan thrust belt, along the northeastern plateau margin, based on detailed analysis and reconstruction of three high-resolution seismic reflection profiles. By integrating surface geology, seismic data, and the regional tectonic history, we demonstrate that this thrust system has accumulated >53% Cenozoic strain (∼50 km shortening), accommodated by several south-dipping thrust faults. Based on the observed strain distribution across northern Tibet, including lower strain (30%–45%) within the interior of the Qilian Shan–Nan Shan thrust belt, we suggest that a combination of distributed crustal shortening and minor (