Multi‐dimensional analyses of the SEAM controlled source electromagnetic data—the story of a blind test of interpretation workflows

Using a subset of the SEG Advanced Modeling Program Phase I controlled‐source electromagnetic data, we apply our standard controlled‐source electromagnetic interpretation workflows to delineate a simulated hydrocarbon reservoir. Experience learned from characterizing such a complicated model offers us an opportunity to refine our workflows to achieve better interpretation quality. The exercise proceeded in a blind test style, where the interpreting geophysicists did not know the true resistivity model until the end of the project. Rather, the interpreters were provided a traditional controlled‐source electromagnetic data package, including electric field measurements, interpreted seismic horizons, and well log data. Based on petrophysical analysis, a background resistivity model was established first. Then, the interpreters started with feasibility studies to establish the recoverability of the prospect and carefully stepped through 1D, 2.5D, and 3D inversions with seismic and well log data integrated at each stage. A high‐resistivity zone is identified with 1D analysis and further characterized with 2.5D inversions. Its lateral distribution is confirmed with a 3D anisotropic inversion. The importance of integrating all available geophysical and petrophysical data to derive more accurate interpretation is demonstrated.     

Importance sampling for efficient modelling of hydraulic loads in the Rhine–Meuse delta

During flood events, breaching of flood defences along a river system can have a significant reducing effect on downstream water levels and flood risks. This paper presents a Monte Carlo based flood risk framework for policy decision making, which takes this retention effect into account. The framework is developed to estimate societal flood risk in terms of potential numbers of fatalities and associated probabilities. It is tested on the Rhine–Meuse delta system in the Netherlands, where floods can be caused by high flows in the Rhine and Meuse rivers and/or high sea water levels in the North Sea. Importance sampling is applied in the Monte Carlo procedure to increase computational efficiency of the flood risk computations. This paper focuses on the development and testing of efficient importance sampling strategies for the framework. The development of an efficient importance sampling strategy for river deltas is more challenging than for non-tidal rivers where only discharges are relevant, because the relative influence of river discharge and sea water level on flood levels differs from location to location. As a consequence, sampling methods that are efficient and accurate for one location may be inefficient for other locations or, worse, may introduce errors in computed design water levels. Nevertheless, in the case study described in this paper the required simulation time was reduced by a factor 100 after the introduction of an efficient importance sampling method in the Monte Carlo framework, while at the same time the accuracy of the Monte Carlo estimates were improved.     

Fluvial dunes: initiation,characterization, flow structure

Research into fluvial dunes spans disciplines, studies at grain to reach scales, and methodological approaches that include theoretical, experimental, numerical and field investigations. Despite significant research efforts to date, it remains difficult to provide definitive answers to some fundamental questions regarding dunes. This paper reviews three notable challenges that remain regarding fluvial dunes, namely scale‐consistent linking of bed morphologies with turbulent flow fields, the intriguing question of what causes trains of highly‐ordered sediment waves to form in beds of river sediments, and how to define the important characteristics of a dune‐covered bed, including lengths, shapes, and their statistical nature. In each case, the particular challenge is discussed and then recent research and ways forward are presented. Copyright © 2010 John Wiley & Sons, Ltd.     

Flat versus steep subduction: Contrasting modes for the formation and exhumation of high- to ultrahigh-pressure rocks in continental collision zones

Flat and steep subduction are end-member modes of oceanic subduction zones with flat subduction occurring at about 10% of the modern convergent margins and mainly around the Pacific. Continental (margin) subduction normally follows oceanic subduction with the remarkable event of formation and exhumation of high- to ultrahigh-pressure (HP–UHP) metamorphic rocks in the continental subduction/collision zones. We used 2D thermo-mechanical numerical models to study the contrasting subduction/collision styles as well as the formation and exhumation of HP–UHP rocks in both flat and steep subduction modes. In the reference flat subduction model, the two plates are highly coupled and only HP metamorphic rocks are formed and exhumed. In contrast, the two plates are less coupled and UHP rocks are formed and exhumed in the reference steep subduction model. In addition, faster convergence of the reference flat subduction model produces extrusion of UHP rocks. Slower convergence of the reference flat subduction model results in two-sided subduction/collision. The higher/lower convergence velocities of the reference steep subduction model can both produce exhumation of UHP rocks. A comparison of our numerical results with the Himalayan collisional belt suggests two possible scenarios: (1) A spatially differential subduction/collision model, which indicates that steep subduction dominates in the western Himalaya, while flat subduction dominates in the extensional central Himalaya; and (2) A temporally differential subduction/collision model, which favors earlier continental plate (flat) subduction with high convergence velocity in the western Himalaya, and later (flat) subduction with relatively low convergence velocity in the central Himalaya.     

Variations in the schumann resonance polarization ellipse in the horizontal and vertical planes according to observations at the Barentsburg and Lovozero observatories

The diurnal variations in the amplitude and parameters of polarization ellipses of the first Schumann resonance according to three magnetic field components, observed on December 1–10, 2007, at the Barentsburg and Lovozero observatories, have been studied. Ellipses have been constructed in the (H, D) and (H, Z) planes. The value of the minor axis, inclination of the major axis, ellipticity, and the rotation direction have been estimated. The vertical magnetic component of the Schumann resonance is three to four times as small as the horizontal component. The difference in the diurnal variations in the ellipse parameters between both observatories has been found. The effect can be caused by a difference in the Earth’s conductivity in the vicinity of the observatories and by conductivity anisotropy. The major axis inclination and ellipticity have semidiurnal components. The polarization vector mostly rotates from D to H in the horizontal plane and from Z to H in the vertical plane at both stations.     

Near-surface geophysics: Complex investigations of the lithosphere-atmosphere interactions

The key trends and problems in the study of interactions between the geospheres in the near-surface areas of the continental crust of the Earth which are of most interest for the formation of living environment are formulated. The main periodicities in the variations of geophysical fields determining the natural environmental rhythms are determined. The interactions and transformations of geophysical fields (electric field in the ground and in the atmosphere, radon emanation field, and the field of microseismic vibrations) are considered. It is noted that the tectonic discontinuities and weak disturbances in the solid Earth such as lunar-solar tides and variations in the atmospheric pressure play an important role in the formation of the regimes of geophysical fields at the boundary of the Earth’s crust and the atmosphere. The synchronous instrumental observations reveal a mutual influence and significant correlation between the amplitude variations of geophysical fields of different nature.     

Catastrophic Tohoku earthquake of March 11, 2011, in Japan

The results of the comparative analysis of parameters of the Tohoku earthquake (Honshu Island, Japan) of March 11, 2011, 05:46 UTC and its aftershocks are presented.     

Eddy covariance imaging of diffuse volcanic CO<Subscript>2</Subscript> emissions at Mammoth Mountain,CA, USA

Use of eddy covariance (EC) techniques to map the spatial distribution of diffuse volcanic CO₂ fluxes and quantify CO₂ emission rate was tested at the Horseshoe Lake tree-kill area on Mammoth Mountain, California, USA. EC measurements of CO₂ flux were made during September–October 2010 and ranged from 85 to 1,766 g m⁻² day⁻¹. Comparative maps of soil CO₂ flux were simulated and CO₂ emission rates estimated from three accumulation chamber (AC) CO₂ flux surveys. Least-squares inversion of measured eddy covariance CO₂ fluxes and corresponding modeled source weight functions recovered 58–77% of the CO₂ emission rates estimated based on simulated AC soil CO₂ fluxes. Spatial distributions of modeled surface CO₂ fluxes based on EC and AC observations showed moderate to good correspondence (R ² = 0.36 to 0.70). Results provide a framework for automated monitoring of volcanic CO₂ emissions over relatively large areas.     

Hydrologic response of underground reservoirs to seismic vibrations

The response of the water level in wells to seismic impacts from remote earthquakes and explosions are analyzed. It is shown that in most cases the magnitude of the postseismic change in the water level scales as a square root of the amplitude of the deformation wave. The intensity of persistent changes averages a dynamical deformation of 1–5 cm/μstrain. Noticeable deviations from the mentioned range are possible, depending on the particular structural features of the layer.     

Pyroclastic deposits from Sarychev Peak,Matua Island discharged in June 2009

We report the first results from a study of pyroclastic material discharged by Sarychev Peak in June 2009 (Matua I., Kuril Is.). We describe the deposits of pyroclastic flows and pyroclastic surges, the ash deposited from the plume of pyroclastic flows, and tephra.