Estimation of changes in water column velocities and thicknesses from time lapse seismic data     

Bård Osdal  Martin Landrø 《Geophysical Prospecting》2011,59(2):295-309

Sea‐bed diffractions are frequently observed for several of the fields in the Norwegian Sea and the Barents Sea. This is a challenge in time lapse seismic analysis, since diffracted multiples are difficult to remove by processing and therefore is a major source of poor time lapse data quality. In this work we test if the diffractions can be used for enhanced 4D interpretation. By analysing the time‐shift of the sea‐bed diffraction hyperbola between the base and monitor it is tested if changes in water velocity and tides can be estimated. Two models using time lapse diffraction analysis are tested: the first one simply adds time‐shifts for the two branches of the diffraction hyperbola and this average time‐shift is then used to estimate the water velocity change. The other method uses an inversion method based on the diffraction equation for a point diffractor to estimate the velocity change. In‐line common‐midpoint shifts are estimated by subtracting the time‐shifts of both hyperbola branches followed by direct inversion. The diffraction based time‐shifts are compared to time‐shifts estimated by standard cross‐correlation of the sea‐bed reflection. The averaging method gives slightly higher uncertainties, while the inversion using an exact traveltime equation gives similar uncertainties compared to the sea‐bed reflection method.  相似文献   

Land uplift effects on the phosphorus cycle of the Baltic Sea     

Andreas C. Bryhn  Lars Håkanson 《Environmental Earth Sciences》2011,62(8):1761-1770

The isostatic land uplift after the latest glaciation period in northern Europe means that the descending wave base in the eutrophicated Baltic Sea continuously exposes new bottom areas to increasing wind and wave-induced erosion. Erosion adds considerable amounts of phosphorus (P) and clay particles to the water column. This study has used a dynamic mass-balance model to investigate how land uplift affects the whole P cycle in the five major subbasins of the Baltic Sea. The model uses a unitary set of variables and constants for all subbasins with the exception of measurable, basin-specific driving variables. Differences in P concentrations between the subbasins could be quite accurately quantified only when the land uplift gradient was used as a driving variable. The clarifying effect from clay particles was found to be a major reason why those subbasins with the most intensive land uplift rates were also the ones with the lowest P concentrations. Without using the land uplift gradient as a model input, concentration differences could not be quantitatively explained in a meaningful way. Furthermore, simulations showed that clay particle erosion from land uplift has a substantial impact on all major internal P fluxes of the Baltic Sea. At the turn of the millennium, one of the subbasins (the Bothnian Bay) was oligotrophic, whilst the other four major subbasins were mesotrophic. Without the clarifying effect from the clay particles added to the water column during erosion of the rising seafloor, all five major subbasins of the Baltic Sea would probably be substantially more eutrophic.  相似文献   

Models of late-type stellar photospheres     

Bengt Gustafsson  Uffe Gråe Jørgensen 《Astronomy and Astrophysics Review》1994,6(1-2):19-65

Summary In this review we discuss recent work and progress in the modelling of photospheres of stars of spectral types F and later. Special emphasis is laid on advances as regards the consideration of atomic and molecular blanketing, non-LTE and convection and other dynamic processes. In a special chapter we discuss the possibilities of semi-empirical modelling of late-type photospheres. In the conclusions we find that much important work remains in this field, but that a considerable part of this work may in fact be carried out in a near future.  相似文献   

Competitive firms in thin regions in Norway: The importance of workplace learning     

Bjørn-Tore Flåten  Arne Isaksen  James Karlsen 《Norsk geografisk tidsskrift. Norwegian journal of geography》2015,69(2):102-111

The article departs from empirical studies of two competitive firms in an organisationally thin region in Norway. The main question in the article is how these firms have achieved global competitiveness. The article focuses its inquiry on how the firms organise their innovation activity, giving special attention to the firms' organisational learning and absorptive capacity. It is found that find that workplace learning enables the firms to utilise knowledge in uncommon ways. The learning rests on specific organisational traits in the firms, such as broad participation, long-term on-the-job training, the use of practice-based knowledge in innovation projects, and links to national and global knowledge sources. The characteristics of thin regions indicate that these traits make up a generally applicable strategy in such regions.  相似文献   

The depositional architecture and facies variability of shelf deltas in the Eocene Battfjellet Formation,Nathorst Land,Spitsbergen     

Sten‐Andreas Grundvåg  William Helland‐Hansen  Erik P. Johannessen  Andreas H. Olsen  Stig A. K. Stene 《Sedimentology》2014,61(7):2172-2204

Deltas are commonly classified according to their plan‐view morphology as either river‐dominated, tide‐dominated or wave‐dominated. However, most deltas form under the mixed influence of these processes, commonly with laterally varying process regimes. It has also become clear that there is a mismatch between the plan‐view morphology and internal facies composition in some deltas. Combined outcrop and subsurface data from the Eocene Battfjellet Formation, Spitsbergen, provide an example of ancient shelf deltas that formed under mixed influence. Internally, these shelf deltas are characterized by wave‐dominated facies that are normally associated with strike‐extensive, nearly linear shoreline sandstones. However, the formation comprises partially overlapping sandstone bodies of limited lateral extent (<20 km in any direction). This stacking pattern is attributed to frequent autogenic lobe switching that caused localized and rapid transgressions. Such processes typify fluvial‐dominated deltas and occur less commonly in wave‐dominated ones. Thus, there is an apparent mismatch between inferred plan‐view morphology and internal facies composition. It is argued that the Battfjellet deltas were flood‐dominated and prograded mainly during periods of high fluvial discharge. However, reworking of the fluvial‐flood facies by fair‐weather and storm waves, as well as longshore currents, resulted in a wave‐dominated facies character. Delta lobes undergoing auto‐retreat were particularly prone to reworking by basinal processes, including tidal currents. It is suggested that repeated delta progradation from inner shelf settings towards the outer shelf and shelf edge was aided by high sediment supply rather than relative falls in sea‐level as previously suggested. This interpretation is supported by: (i) the lack of major facies dislocations and extensive sub‐aerial unconformities; and (ii) an overall relative rise in sea‐level as evidenced by an overall low‐angle (0·8 to 1·2°) ascending shoreline trajectory. The latter results from the combined effect of basin subsidence, eustatic highstand and sediment compaction.  相似文献   

Rock Mass Grouting in the Løren Tunnel: Case Study with the Main Focus on the Groutability and Feasibility of Drill Parameter Interpretation     

Are Håvard Høien  Bjørn Nilsen 《Rock Mechanics and Rock Engineering》2014,47(3):967-983

The Løren road tunnel is a part of a major project at Ring road 3 in Oslo, Norway. The rock part of the tunnel is 915 m long and has two tubes with three lanes and breakdown lanes. Strict water ingress restriction was specified and continuous rock mass grouting was, therefore, carried out for the entire tunnel, which was excavated in folded Cambro-Silurian shales intruded by numerous dykes. This paper describes the rock mass grouting that was carried out for the Løren tunnel. Particular emphasis is placed on discussing grout consumption and the challenges that were encountered when passing under a distinct rock depression. Measurement while drilling (MWD) technology was used for this project, and, in this paper, the relationships between the drill parameter interpretation (DPI) factors water and fracturing are examined in relation to grout volumes. A lowering of the groundwater table was experienced during excavation under the rock depression, but the groundwater was nearly re-established after completion of the main construction work. A planned 80-m watertight concrete lining was not required to be built due to the excellent results from grouting in the rock depression area. A relationship was found between leakages mapped in the tunnel and the DPI water factor, indicating that water is actually present where the DPI water factor shows water in the rock. It is concluded that, for the Løren tunnel, careful planning and high-quality execution of the rock mass grouting made the measured water ingress meet the restrictions. For future projects, the DPI water factor may be used to give a better understanding of the material in which the rock mass grouting is performed and may also be used to reduce the time spent and volumes used when grouting.  相似文献   

An Iterative Method for Calculation of Wind Profiles at the Mesoscale and Microscale     

Adamiec-Wójcik  Iwona  Brzozowska  Lucyna  Drąg  Łukasz  Wojciech  Stanisław 《Boundary-Layer Meteorology》2022,184(3):423-440

Boundary-Layer Meteorology - Space–time correlations are fundamental to statistical theories and turbulence modelling. However, experimental studies of space–time correlations are often...  相似文献   

基于AO的分幅等高线智能化接边处理方法的研究   总被引：9，自引：0，他引：9  

邓小军  郑小梅 《四川测绘》2004,27(2):77-81

连续完整的等高线在DEM的制作以及图属互查中起着重要的作用，然而在实际中它往往被人为的分割。因此，分幅数字化后的等高线拼接问题，就成了地理信息系统中基础数据处理方面的一个必须要解决的问题。本文在吸取了ArcGIS处理该问题的优点的基础上，提出了分幅等高线智能化接边的约束条件和算法，并利用ArcObjects(简称AO)实现该处理方法。  相似文献   

Lithology and fluid prediction from prestack seismic data using a Bayesian model with Markov process prior     

Hugo Hammer  Odd Kolbjørnsen  Håkon Tjelmeland  Arild Buland 《Geophysical Prospecting》2012,60(3):500-515

We invert prestack seismic amplitude data to find rock properties of a vertical profile of the earth. In particular we focus on lithology, porosity and fluid. Our model includes vertical dependencies of the rock properties. This allows us to compute quantities valid for the full profile such as the probability that the vertical profile contains hydrocarbons and volume distributions of hydrocarbons. In a standard point wise approach, these quantities can not be assessed. We formulate the problem in a Bayesian framework, and model the vertical dependency using spatial statistics. The relation between rock properties and elastic parameters is established through a stochastic rock model, and a convolutional model links the reflectivity to the seismic. A Markov chain Monte Carlo (MCMC) algorithm is used to generate multiple realizations that honours both the seismic data and the prior beliefs and respects the additional constraints imposed by the vertical dependencies. Convergence plots are used to provide quality check of the algorithm and to compare it with a similar method. The implementation has been tested on three different data sets offshore Norway, among these one profile has well control. For all test cases the MCMC algorithm provides reliable estimates with uncertainty quantification within three hours. The inversion result is consistent with the observed well data. In the case example we show that the seismic amplitudes make a significant impact on the inversion result even if the data have a moderate well tie, and that this is due to the vertical dependency imposed on the lithology fluid classes in our model. The vertical correlation in elastic parameters mainly influences the upside potential of the volume distribution. The approach is best suited to evaluate a few selected vertical profiles since the MCMC algorithm is computer demanding.  相似文献   

Quake Catalogs from an Optical Monitoring of an Interfacial Crack Propagation     

M. Grob  J. Schmittbuhl  R. Toussaint  L. Rivera  S. Santucci  K. J. Måløy 《Pure and Applied Geophysics》2009,166(5-7):777-799

Using an experimental setup which allows to follow optically the propagation of an interfacial crack front in a heterogeneous medium, we show that the fracture front dynamics is governed by local and irregular avalanches with large velocity fluctuations. Events defined as high velocity bursts are ranked in catalogs with analogous characteristics to seismicity catalogs: time of occurence, epicenter location and energy parameter (moment). Despite differences in the fracturing mode (opening for the experiments and shear rupture for earthquakes), in the acquisition mode and in the range of time scales, the distributions of moment and epicenter jumps in the experimental catalogs obey the same scaling laws with exponents similar to the corresponding distributions for earthquakes. The record-breaking event analysis also shows very strong similarities between experimental and real seismicity catalogs. The results suggest that the dynamics of crack propagation is controlled by the elastic interactions between microstructures within the material.  相似文献