Collapse of the fishery for Iceland scallop (Chlamys islandica) in Breidafjordur, West Iceland     

Jonasson  Jonas P.; Thorarinsdottir  Gudrun; Eiriksson  Hrafnkell; Solmundsson  Jon; Marteinsdottir  Gudrun 《ICES Journal of Marine Science》2007,64(2):298-308

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Drift probabilities for Icelandic cod larvae   总被引：1，自引：0，他引：1  

Brickman  David; Marteinsdottir  Gudrun; Logemann  Kai; Harms  Ingo H. 《ICES Journal of Marine Science》2007,64(1):49-59

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New Holocene tephras and a proxy climate record from a blanket mire in northern Skye,Scotland     

P. G. Langdon  K. E. Barber 《第四纪科学杂志》2001,16(8):753-759

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Constraints on crustal and mantle structure of the oceanic plate south of Iceland from ocean bottom recorded Rayleigh waves     

Frederik J. Tilmann  Torsten Dahm 《Tectonophysics》2008,447(1-4):66

From April to July 2002 we carried out a deployment of 6 ocean bottom seismometers and 4 ocean bottom hydrophones in the North Atlantic south of Iceland. During the deployment period we recorded clear Rayleigh waves from 2 regional and 14 teleseismic earthquakes. This corresponds to a Rayleigh wave detection rate of nearly 92% for events with M_W ≥ 6.06.0 and epicentral distance less than 110°, close to detection rate estimates based on noise level variability. We measured Rayleigh wave event-station group dispersion and inter-station phase dispersion for one Mid-Atlantic Ridge event. The group dispersion curve is sensitive to the structure of the North-East Atlantic with an average age of  39 Myr. The phase dispersion curve is sensitive to the structure just south of Iceland (average plate age 33 Myr). Both dispersion curves indicate faster velocities than previously postulated for oceanic plate generated at the Reykjanes Ridge. A grid search approach was used to constrain the range of models fitting the data. The high velocity seismic lid just south of Iceland in the model for the phase dispersion path is slower or thinner than in the group dispersion model, which averages over a larger area and a somewhat older plate age, but the velocities in the low velocity half space are similar. We further consider the residual bathymetry in the experimental area. The residual anomaly decreases by 300–400 m from the Reykjanes Ridge to the  30 Myr old plate south of Iceland. This decrease can be explained by the disappearance of a mantle thermal anomaly associated with the Iceland plume. Both the residual bathymetry and the surface wave data are thus consistent with the notion that the southward spreading of the Icelandic plume is channelised underneath the Reykjanes Ridge and does not spread far outside this channel.Based on the experience from the pilot experiment, we estimate that a minimum recording time of 13–15 months in favourable weather conditions (April–September) is required to record enough data to map the spreading plume with surface waves, and to produce a tomographic image to a depth of 1000 km using body waves. This can be achieved by a continuous deployment of at least  20 months, or by two or three deployments during the spring and summer of consecutive years.  相似文献   

Calculating horizontal stress orientations with full or partial knowledge of the tectonic stress tensor   总被引：3，自引：0，他引：3  

Björn Lund  John Townend 《Geophysical Journal International》2007,170(3):1328-1335

Earthquakes potentially serve as abundant and cost-effective gauges of tectonic stress provided that reliable means exist of extracting robust stress parameters. Several algorithms have been developed for this task, each of which typically provides information on the orientations of the three principal stresses and a single stress magnitude parameter. A convenient way of displaying tectonic stress results is to map the azimuth of maximum horizontal compressive stress, which is usually approximated using the azimuth of the larger subhorizontal principal stress. This approximation introduces avoidable errors that depend not only on the principal stress axes' plunges but also on the value of the stress magnitude parameter. Here we outline a method of computing the true direction of maximum horizontal compressive stress ( S _H) and show that this computation can be performed using only the four stress parameters obtained in routine focal mechanism stress estimation. Using theoretical examples and new stress inversion results obtained with focal mechanism data from the central Grímsey lineament, northern Iceland, we show that the S _H axis may differ by tens of degrees from its commonly adopted proxy. In order to most appropriately compare tectonic stress estimates with other geophysical parameters, such as seismic fast directions or geodetically measured strain rate tensors, or to investigate spatiotemporal variations in stress, we recommend that full use be made of the routinely estimated stress parameters and that a formal axis of maximum horizontal compression be calculated.  相似文献   

Macroseismic effects related to strong ground motion: a study of the South Iceland earthquakes in June 2000   总被引：1，自引：1，他引：1  

R. Sigbjörnsson  S. Ólafsson  J. Th. Snæbjörnsson 《Bulletin of Earthquake Engineering》2007,5(4):591-608

The impact of the June 2000 South Iceland earthquakes has been assessed applying data collected in field surveys and strong-motion recordings from the Icelandic Strong-Motion Network. The areas within approximately 20 km of the causative faults suffered considerable damage, including transportation and utility systems as well as buildings, both with regard to structure and inventories. Ground subsidence and dislocations were significant in the near-fault zone. Aftershocks and permanent displacements of building foundations resulted in progressive structural damage. By introducing holistic measures derived from the acceleration data, a fair correlation was achieved between the obtained earthquake intensities and the recorded accelerations. The measures adopted were square root of the sum of the squares (SRSS) values of peak ground acceleration (PGA) and the trace of the Arias intensity tensor. It was found that the overall attenuation tended to be more rapid than reflected by common strong-motion models reported in the literature. There is no simple explanation for this behaviour but it is reasonable to suggest that it can be partly attributed to the heterogeneous and fractured crust that is characteristic of Icelandic geology.  相似文献   

Decadal to millennial-scale periodicities in North Iceland shelf sediments over the last 12 000 cal yr: long-term North Atlantic oceanographic variability and solar forcing     

John T. Andrews  Jorunn Hardadottir  Joseph S. Stoner  Michael E. Mann  Greta B. Kristjansdottir  Nalan Koc 《Earth and Planetary Science Letters》2003,210(3-4):453-465

Giant piston core MD99-2269 recovered 25 m of sediment in Hunáfloáall, a deep trough on the North Iceland margin fronting the Iceland Sea, and the site of a shelf sediment drift. The rate of sediment accumulation is 2 m/kyr (5 yr/cm); the core terminated in the Vedde tephra (12 cal ka). The sediment was sampled at between 5 and 50 yr/sample, including rock magnetic, grain-size, and sediment properties. Data reduction was carried out using principal component analysis. Two PC axes for the 5-yr/sample magnetic data are strongly correlated with measures of coercivity (ARM_{20 mT}/ARM) and magnetic concentrations (kARM). In turn ARM_{20 mT}/ARM is highly correlated (negatively) with grain-size and the mean size of the sortable silt fraction. Analyses of the two PC axes with MTM spectral methods indicate a series of significant (>99%) periodicities at millennial to multidecadal scales, including those at 200, 125, and 88 yr which are associated with solar variability. We also document a strong correlation between the sediment magnetic properties and the ∂¹⁸O on benthic foraminifera on the North Iceland inner shelf. We hypothesize that the links between variations in grain-size, magnetic concentrations, and solar forcing are controlled by atmospheric and oceanographic changes linked to changes in the relative advection of Atlantic and polar waters along the North Iceland margin. Today these changes are associated with variations in the deep convection in the Greenland and Iceland Seas. The precise linkages are, however, presently elusive although a combination of coarser sediments and low ∂¹⁸O values define a Holocene thermal maximum between 8 and 6 cal ka.  相似文献   

Shape and size of the starting Iceland plume swell     

Stephen M. Jones  Nicky White 《Earth and Planetary Science Letters》2003,216(3):271-282

Emplacement of a large igneous province is usually accompanied by kilometre-scale uplift over an area of ∼10⁶ km². We have developed a method for mapping the dynamically supported swell associated with the North Atlantic Igneous Province by inverting palaeo-topographic information from continental margins. In the forward model, latest Palaeocene palaeo-topography around Britain and Ireland is calculated by correcting present-day topography for global sea-level change, denudation and dynamic support. We initially assume a Gaussian, axially symmetric dynamic support profile. Modelled coastlines are compared with palaeo-coastlines mapped on 2D and 3D reflection seismic data. In the inverse model, the amplitude, width and centre of the dynamically supported swell are determined by minimising misfit between modelled and observed coastlines. Uncertainties associated with global sea-level variation and denudation have little effect on this calculation. The best-fit dynamic support profile from inverting palaeo-coastline positions is in good agreement with dynamic support estimates from subsidence anomalies measured in extensional sedimentary basins fringing Britain and Ireland. However, a circular planform of dynamic support cannot simultaneously account for palaeo-coastlines, subsidence anomalies and the spatial extent of the North Atlantic Igneous Province. In combination, these data suggest that the swell was more irregular in planform. This inference can be tested in future by modelling stratigraphic data from offshore Norway, Greenland and Canada. The large areal extent and short time interval for inflation of the dynamically supported swell are best explained by rapid convective emplacement of an abnormally hot mantle layer horizontally beneath the lithosphere, during the starting phase of the Icelandic convective system. We emphasise the need to interpret the igneous record jointly with the dynamic support history when discussing models of large igneous province formation and mantle convection.  相似文献   

A study of the palaeomagnetism of subglacial basalts, SW Iceland: a comparison with oceanic crust     

J. Helgason  N. A. Van Wagoner  P. J. C. Ryall 《Geophysical Journal International》1990,103(1):13-24

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Microstructural changes accompanying the opal-A to opal-CT transition: new evidence from the siliceous sinters of Geysir, Haukadalur, Iceland   总被引：2，自引：0，他引：2  

BRIAN JONES  ROBIN W. RENAUT† 《Sedimentology》2007,54(4):921-948

Opaline silica (opal-A) has formed in marine, lacustrine and geothermal environments throughout geological time. During diagenesis opal-A normally changes to opal-CT, then opal-C, and finally to quartz. Such changes commonly destroy the original fabrics and any fossils that opal-A contained. The physical changes that accompany the opal-A to opal-CT transition, however, are known poorly. X-ray diffraction analyses, electron microprobe analyses and high-resolution, high-magnification scanning electron microscope imagery of siliceous sinters from the Geysir geothermal area in Iceland show that opal-A is formed of heterometric arrays of randomly packed microspheres (up to 5  μ m diameter) with neighbouring spheres commonly being joined by small connection pads. In contrast, enlarged spheres, lepispheres, inverse opal (two types) and spindle frameworks with hexagonal motifs characterize opal-CT. The textures in opal-CT, which vary on a microscale, reflect the complex interplay between dissolution (e.g. inverse opal) and precipitation (e.g. enlarged spheres, spindle frameworks) that probably was mediated by groundwater in a near-surface environment. The processes deciphered from these young rocks should, however, be applicable to sedimentary opal-A and opal-CT of all ages, irrespective of their origin.  相似文献