1,720,972 research outputs found
Seismic inversion for site characterization: When, where and why should we use it?
No full textThe application of seismic inversion techniques to the foundation and drilling top hole zones has garnered significant interest in recent years. The shift towards more geologically complex and deeper water sites, combined with the global economic climate, has driven a requirement for more cost-effective site characterisation. More often used by the exploration industry, seismic inversion has been touted as a potentially valuable tool for quantifying the spatial and depth variability in sediment properties. In doing so, this approach can reduce the risk of encountering unforeseen ground conditions and the need for excessive over-design. Despite its potential, the inversion of high-resolution seismic data has yet to see widespread use, leaving unanswered questions regarding how and where this tool can best fit into the site characterization work flow. We test the potential usefulness of seismic inversion using a range of existing site investigation data sets. We apply several different inversion methods, including acoustic impedance and seismic quality factor inversion, as well as artificial neural network multi-attribute regression, to tackle end-member potential uses. First, explore early-phase potential uses, showing how seismic quality factor and acoustic impedance inversion can be used to capture the spatial variability in facies architecture and bulk sediment properties that could be used in appraisal and pre-FEED studies to optimize borehole and penetrometer (CPT) depths/locations and to ensure effective site-wide characterization. Second, we apply a combined acoustic impedance and artificial neural network workflow to link seismic properties with CPT profiles. These results demonstrate the potential late-phase use of seismic inversion for short-range interpolation/extrapolation of more complex geotechnical properties through the generation of synthetic CPT profiles useful for infrastructure design and micro-siting late in the development cycle. While not a comprehensive list of applications, together these examples illustrate how seismic inversion can be utilized throughout the development cycle. If the required objectives are clearly defined and an appropriate inversion workflow developed, seismic inversion can help to reduce uncertainty in site-wide characterization and drive efficiencies in layout and design studies throughout a project lifetime
High-resolution seismic imaging of a Younger Dryas and Holocene mass movement complex in glacial lake Windermere, UK
Get PDFThe stratigraphy and sedimentological processes operating over the last 15,000 years within glacial lake Windermere (UK), at the mouth of Cunsey Beck, were imaged by a decimetre-resolution seismic reflection survey. A complex of fifteen mass movement deposits was identified as contemporaneous with the Younger Dryas, and two within the overlying Holocene drape. The high vertical resolution and dense grid of profiles allowed pseudo three-dimensional mapping of individual events, along with the determination of their relative temporal relationships. The size of the mass wasting deposits has been estimated to range between 2100 and > 100,000 m3. The geometry, structure and relationship to the existing stratigraphy suggest a rapid emplacement of the Younger Dryas mass movement deposits, facilitated by climatic changes making subaqueous slopes unstable, with possible triggering by seismic activity. Morphometric parameters, such as volume and planar surface area, indicate a greater mobility of the Younger Dryas mass movement deposits compared to the Holocene events. The sediments of all imaged mass movement deposits are believed to originate from the slope deposits of the lake. The age of two Holocene mass movement deposits, triggered by flooding or terrestrial debris flows, is estimated to be 2400 and 4400 years BP
Characterisation of shallow overpressure in consolidating submarine slopes via seismic full waveform inversion
No full textPore pressures higher than hydrostatic correspond to localized reductions of the level of shear stress required to induce lateral mass movement in a slope, and therefore play a key role in preconditioning submarine landsliding. In this paper, we investigate whether multi-channel seismic reflection data can be used to infer potentially destabilizing pore-pressure levels at a resolution and sensitivity useful for in-situ slope stability characterization. We simulate the continuous deposition of sediment on consolidating slopes in two scenarios, with combinations of sedimentation rate and permeability distribution leading to disequilibrium compaction. Ultra-high-frequency (UHF; 0.2–2.5 kHz) seismic reflection data are computed for each model and a stochastic full waveform inversion (FWI) method is used to retrieve the sub-seabed properties from the computed seismograms. These are then interpreted as time–depth variations in the effective stress (σ′) regime, and therefore local overpressure ratio and factor of safety, using a combination of p-wave velocity to σ′ transforms. The results demonstrate that multi-channel UHF seismic data can provide valuable constraints on the distribution of physical properties in the top 50 m below seabed at a sub-metric scale, and with a sensitivity useful to infer destabilizing excess pore pressure levels.</p
Pre-stack waveform inversion of VHF marine seismic data. A case study in Norway
No full textA quantitative physical model of the shallow marine sediments is of crucial importance in broad range of environmental and engineering contexts, from the assessment of tsunamigenic landslides hazard and off-shore structure stability, to the identification and monitoring of carbon capture and storage sites. However, in contrast to reservoir geophysics, where quantitative seismic interpretation and inversion are extensively employed tools, sub-seabed characterisation is still heavily reliant on direct samplings, using cores, boreholes and CPTUs. In this context, the role of seismic reflection is often limited to a mostly qualitative interpretation of the reflection architecture.Here we will present the first published application of pre-stack elastic full waveform inversion to a Very-High-Frequency (VHF, 0.4 – 2.5 kHz) multi-channel seismic reflection dataset. A custom-built local multi-parameter sequential waveform inversion method has been developed and tested on two common-shot gathers from a multi-channel Boomer seismic profile acquired in northern Norway. The decimetre-resolution impedance and Poisson’s ratio obtained models strongly agree with the a-priori geotechnical and geological information available in the area, proving the potential of the method in obtaining an accurate remote characterisation of the shallow sediments within a reasonable computational cost and using a traditional multi-channel sub-bottom profiler
State-of-the-art remote characterization of shallow marine sediments: the road to a fully integrated solution
No full textCurrent methods for characterizing near-surface marine sediments rely on extensive coring/penetrometer testing and correlation to seismic facies. Little quantitative information is regularly derived from geophysical data beyond qualitative inferences of sediment characteristics based on seismicfacies architecture. Even these fundamental seismostratigraphic nterpretations can be difficult to correlate with lithostratigraphic data due to inaccuracies in the time-to-depth conversion of geophysical data and potential loss and/or compression of high-porosity and under-consolidated seafloor material during direct sampling. To complicate matters further, when quantitative information is derived from marine geophysical data, it often describes the sediments using terminology (e.g., acoustic impedance and seismic quality factor) that is impenetrable to geologists and engineers. Incontrast, for hydrocarbon prospecting, reservoir characterization using quantitative inversion of geophysical data has developed enormously over the past 20 years or more. Impedance and amplitude-versus-angle inversion techniques are now commonplace, whereas computationally expensive waveform inversions are gaining traction, and there is a well-developed interface between these geophysical and reservoir engineering fields via rock physics.In this paper, we collate and review the different published inversion methods for high-resolution geophysical data. Using several case study examples spanning a broad range of depositional environments, we assess the current state of the art in remote characterization of shallow sediments from a multidisciplinary viewpoint, encompassing geophysical, geological, and geotechnical angles. By identifying the key parameters used to characterize the subsurface, a framework is developed whereby geological, geotechnical, and geophysical characterizations of the subsurface can berelated in a less subjective manner. As part of this, we examine the sensitivity of commonly derived acoustic properties (e.g., acoustic impedance and seismic quality factor) to more fundamentally important soil properties (e.g., lithology, pore pressure, gas saturation, and undrained shear strength), thereby facilitating better integration between geological, geotechnical, and geophysical data for improved mapping of sediment properties. Ultimately, we present a number of ideas for future research activities in this field.<br/
Morphodynamic evolution of Kongsfjorden-Krossfjorden, Svalbard, during the Late Weichselian and Holocene
No full textWe present a combination of fjord bathymetry and shallow seismic data from Kongsfjorden and Krossfjorden, Svalbard, to characterize and analyse change in the fjord coastal environment physiography and the glaciosedimentary processes since the Last Glacial Maximum. Swath bathymetry reveals a series of several styles of landform, frequently superimposed upon each other, permitting the reconstruction of the relative timings of deposition of each landform with the oldest successively overlain and cross-cut by younger landforms and erosional processes. Large transverse ridges interpreted as recessional moraines are overlain by streamlined lineations formed subglacially during a subsequent ice advance. A complex of recessional morainal ridges occurring within the central fjord are incised by glacial lineations and meltwater channels from younger glacial events
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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