Earthquake response of a base-isolated bridge subjected to strong near-fault ground motion     

Magni Hreinn Jónsson  Bjarni Bessason  Einar Haflidason 《Soil Dynamics and Earthquake Engineering》2010

The South Iceland Lowland is an active seismic zone. In May 2008 a magnitude 6.3 (M_w) earthquake struck the area. The 370-m-long base-isolated Oseyrar Bridge situated close to the epicentre was hit by strong ground motion. Concrete stoppers at the top of all piers were badly smashed and all four wing walls of the abutments were severely damaged. The study showed that it is possible with numerical models to back-calculate the observed damage based on recorded ground motion in the area. The recorded loads were larger than prescribed by Eurocode 8 for the site even though the magnitude and location of the earthquake was as expected. The main reason was a near-fault pulse which is not covered in the code. The pulse dominated the bridge response and is therefore important to consider. Finally, an improved design is presented that could have prevented the damage.  相似文献   

The nature of quiescent solar prominences     

Max Kuperus  Einar Tandberg-Hanssen 《Solar physics》1967,2(1):39-48

Quiescent prominences occur as long-lasting cool sheets of matter in the surrounding hot corona at the base of coronal streamers. Seen on the disk they appear as dark filaments dividing regions of opposite magnetic polarity.In this paper a theoretical model is presented, which describes the general appearance of quiescent prominences.It is shown that the neutral sheet between two regions of oppositely directed magnetic fields is thermally unstable. This gives rise to compression and cooling of coronal material to prominence material in a characteristic time of the order of one day for a field strength of 0.5 gauss in the lower corona.It is assumed that due to the finite electrical resistivity of the plasma, filamentary structures are formed by the tearing-mode resistive plasma instability. These structures are thermally insulated from the hot surroundings by the newly formed closed azimuthal magnetic field configuration.It has been shown that for fine structures with a diameter of 300 km the growth rate of the tearing-mode instability is of the same order as the cooling time. The occurrence of fine structures within the prominence is of vital importance for their origin.On leave from the Observatory Sonnenborgh at Utrecht, The Netherlands.  相似文献   

Refugee Camp Mapping Using Very High Spatial Resolution Satellite Sensor Images     

Einar Bjorgo 《国际地球制图》2013,28(2):79-88

Abstract

Short time‐intervals for complex response in unfamiliar areas cause refugee‐relief organisations to have a strong need for timely and up‐to‐date geographic information of the environment during humanitarian operations. The objective of this study is to provide an overview of relief organisations' need for detailed geographic information, and to assess the potential of the upcoming very high spatial resolution (VHSR) satellite sensors to provide this geographic information by mapping refugee camps and their environment on an operational basis. To demonstrate the use of VHSR satellite technology in relief operations, a pilot proof‐of‐concept study using a 1992 Russian KVR‐lOOO 2 m resolution panchromatic image of the six refugee camps in the Qala en Nahal settlement scheme in the Sudan was performed. The VHSR satellite sensor image was found to be useful for mapping refugee camp environmental parameters, such as land use, roads, rivers, and water sources, as well as camp infrastructure, including geographic positioning of camps, housing, and street network. The image also allowed for detailed camp area estimates. In addition, a statistically significant relationship between camp area and population was revealed for refugee camps included in this study. In operational use of VHSR satellite sensor data, relief agencies should be aware of the limitations of optical satellite images, in particular their reduced applicability during cloudy conditions.  相似文献   

Event-oriented velocity estimation based on prestack data in time or depth domain1     

Einar Iversen  Hvar Gjystdal 《Geophysical Prospecting》1996,44(4):643-686

A 2D reflection tomographic method is described, for the purpose of estimating an improved macrovelocity field for prestack depth migration. An event-oriented local approach of the ‘layer-stripping’ type has been developed, where each input event is defined by its traveltime and a traveltime derivative, taken with respect to one of four coordinates in the source/receiver and midpoint half-offset systems. Recent work has shown that the results of reflection tomography may be improved by performing event picking in a prestack depth domain. We adopt this approach and allow events to be picked either before or after prestack depth migration. Hence, if events have been picked in a depth domain, such as the common-shot depth domain or the common-offset depth domain, then a depth-time transformation is required before velocity estimation. The event transformation may, for example, be done by conventional kinematic ray tracingr and with respect to the original depth-migration velocity field. By this means, we expect the input events for velocity updating to become less sensitive to migration velocity errors. For the purpose of velocity estimation, events are subdivided into two categories; reference horizon events and individual events. The reference horizon events correspond to a fixed offset in order to provide basic information about reflector geometry, whereas individual events, corresponding to any offset, are supposed to provide the additional information needed for velocity estimation. An iterative updating approach is used, based on calculation of derivatives of event reflection points with respect to velocity. The event reflection points are obtained by ray-theoretical depth conversion, and reflection-point derivatives are calculated accurately and efficiently from information pertaining to single rays. A number of reference horizon events and a single individual event constitute the minimum information required to update the velocity locally, and the iterations proceed until the individual event reflection point is consistent with those of the reference horizon events. Normally, three to four iterations are sufficient to attain convergence. As a by-product of the process, we obtain so-called uncertainty amplification factors, which relate a picking error to the corresponding error in the estimated velocity or depth horizon position. The vector formulation of the updating relationship makes it applicable to smooth horizons having arbitrary dips and by applying velocity updating in combination with a flexible model-builder, very general macro-model structures can be obtained. As a first step in the evaluation of the new method, error-free traveltime events were generated by applying forward ray tracing within given macrovelocity models. When using such ‘perfect’ observations, the velocity estimation algorithm gave consistent reconstructions of macro-models containing interfaces with differential dip and curvature, a low-velocity layer and a layer with a laterally varying velocity function.  相似文献   

Review of Ray Theory Applications in Modelling and Imaging of Seismic Data     

Gjøystdal  Håvar  Iversen  Einar  Laurain  Renaud  Lecomte  Isabelle  Vinje  Vetle  Åstebøl  Ketil 《Studia Geophysica et Geodaetica》2002,46(2):113-164

Throughout the last twenty years, 3D seismic ray modelling has developed from a research tool to a more operational tool that has gained growing interest in the petroleum industry. Various areas of application have been established and new ones are under development. Many of these applications require a modelling system with flexible, robust and efficient modelling algorithms in the core. The present paper reviews the basic elements of such a system, based on the open model concept and the wavefront construction technique. In the latter, ervený's dynamic ray tracing is an intrinsic part. The modelling system can be used for generating ray attributes and synthetic seismograms for realistic 3D surveys with tens of thousands of shots and receivers. Moreover, some other types of application areas are illustrated: Production of Green's functions for prestack depth migration and hybrid modelling (combined ray and finite-difference modelling), attribute mapping and illumination analysis, both for survey planning and interpretation. Finally, the concepts of isochron rays and velocity rays related to seismic isochrons have been introduced recently, with very interesting future applications.  相似文献   

The origin of Skagerrak coastal water off Arendal in relation to variations in nutrient concentrations     

Aure  Jan; Danielssen  Didrik; Svendsen  Einar 《ICES Journal of Marine Science》1998,55(4):610-619

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A decade of ITQ-management in Icelandic fisheries: consolidation without consensus     

Einar Eythrsson 《Marine Policy》2000,24(6):658

Icelandic fisheries have been managed by individual transferable quotas (ITQs) for a decade but there is still no consensus about the quota issue. Distributional effects of ITQs, in terms of income distribution between owner and crew, and the vulnerability of fisheries communities short of quota, have been in the centre of the debate.The author discusses changes in stakeholder involvement in policy-making, conflicts of interest and legal disputes linked to the ITQ-system. By way of conclusion, some options for resolving conflicts and reaching consensus on the fisheries management issue are discussed.  相似文献   

Green corona emission,calcium plage activity and solar sector magnetism     

Arild Gulbrandsen  Einar Gjøen  Helge Dalseide 《Planetary and Space Science》1976,24(9):883-891

The relationship between coronal green line emission and solar sector magnetism has been studied statistically for the years 1965–1969. This period includes the rising portion and the maximum phase of solar cycle no. 20. In the years around solar maximum the results suggest the existence of longitudinal magnetic arcades at the solar sector boundaries. The arcades extend from at least 50°N to 50°S and are flanked by north-south oriented coronal holes about 90° apart. In the rising portion of the cycle the general picture consists of a high green line intensity structure to the west of the boundary and a region of low intensity several days wide to the east of it.Analyses of the calcium plage distribution in the years 1962–1969 show that, on the average, there is a tendency for the plage activity to peak near the sector boundaries. It is further concluded that the activity distribution suggested by Wilcox (1971a, b) is not typical of the behaviour of solar activity relative to the sector boundaries.  相似文献   

Exploring Geovisualization Symbology for Landscape Genetics     

Eoin Mac Aoidh  Jann Th. Martinsohn  Gregory E. Maes  Alessia Cariani  Einar E. Nielsen 《Transactions in GIS》2013,17(2):267-281

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Magnetic fields in quiescent prominences     

Einar Tandberg-Hanssen 《Solar physics》1970,15(2):359-371

We discuss the longitudinal component of the magnetic field, B , based on data from about 135 quiescent prominences observed at Climax during the period 1968–1969. The measurements are obtained with the magnetograph which records the Zeeman effect on hydrogen, helium and metal lines. Use of the following lines, H; Hei, D₃, Hei, 4471 Å; Nai, Di and D₂, leads to the same value for the observed magnetic field component in these prominences. For more than half of the prominences their mean field, B , satisfy the inequalities 3 G B 8 G, and the overall mean value for all the prominences is 7.3 G. As a rule, the magnetic field enters the prominence on one side and exits on the other, but in traversing the prominence material, the field tends to run along the long axis of the prominence.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献