Thermal condition of Surtsey     

V. Stefansson  G. Axelsson  O. Sigurdsson  G. Gudmundsson  B. Steingrimsson 《Journal of Geodynamics》1985,4(1-4)

The island Surtsey was created by a submarine volcanic eruption which started on the 14th of November 1963, 21 km southwest of the Westman Islands. Volcanic activity continued in this area for nearly 4 years. During the summer of 1979 a 181 m deep continuously cored borehole was drilled on the Surtsey island. Several temperature profiles have been measured in the hole since 1979. The results of these temperature measurements are used as the basis for a discussion of the thermal condition of Surtsey. The hypothesis that intrusions rather than pillow lavas are responsible for the excess heat content of Surtsey is favored. It is found that the 13 m thick discontinuous dike complex, observed in the drill core, is sufficient to explain the excess heat content in the vicinity of the borehole and the shape of the temperature profiles recorded. It is demonstrated that the heat transfer in Surtsey has been dominated by hydrothermal convection and that the system is vapor dominated above sea level. It is estimated that the permeability of a 40 m thick section of altered tuff below sea level is 4.1 × 10⁻¹³ m², while the permeability of the unaltered tuff above sea level is estimated as 1.2 × 10⁻¹⁰ m².  相似文献   

Application of arma models to estimate earthquake ground motion and structural response     

Símon lafsson  Ragnar Sigbjrnsson 《地震工程与结构动力学》1995,24(7):951-966

This paper deals with the use of ARMA models in earthquake engineering. Tools and methods applied to strong ground motion are discussed emphasizing simulation of probabilistic earthquake response spectra. The ARMA models are applied to Icelandic earthquake data and a tentative model for Icelandic earthquakes is presented. This model, which is derived using 54 accelerograms, is based on a low-order, time-invariant ARMA process excited by Gaussian white noise and amplitude modulated using a simple envelope function to account for the non-stationary characteristics. This simple model gives a reasonable fit to the observed ground motion. Further, this model produces accurate earthquake response spectra, which, combined with accompanying attenuation and duration formulae, might be useful in earthquake hazard and risk assessment.  相似文献   

Economic instruments for achieving ecosystem objectives in fisheries management   总被引：1，自引：0，他引：1  

Arnason  Ragnar 《ICES Journal of Marine Science》2000,57(3):742-751

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Methodology for geohazard assessment for hydropower projects   总被引：1，自引：0，他引：1  

Fjóla G. Sigtryggsdóttir  Jónas Th. Snæbjörnsson  Lars Grande  Ragnar Sigbjörnsson 《Natural Hazards》2015,79(2):1299-1331

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Genetic divergence among East Icelandic and Faroese populations of Atlantic cod provides evidence for historical imprints at neutral and non-neutral markers     

Pampoulie  Christophe; Steingrund  Petur; Stefansson  Magnus O.; Danielsdottir  Anna K. 《ICES Journal of Marine Science》2008,65(1):65-71

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A successfully stress-forecast earthquake   总被引：21，自引：0，他引：21  

Stuart Crampin  Theodora Volti  & Ragnar Stefánsson 《Geophysical Journal International》1999,138(1):F1-F5

A M = 5 earthquake in Iceland has been successfully 'stress forecast' by using variations in time delays of seismic shear wave splitting to assess the time and magnitude at which stress-modified microcracking reaches fracture criticality within the stressed volume where strain is released. Local investigations suggested the approximate location of the forecast earthquake. We report the criteria on which this stress forecast was based.  相似文献   

Assessment of ground motion variability and its effects on seismic hazard analysis: a case study for iceland   总被引：1，自引：1，他引：0  

Teraphan Ornthammarath  John Douglas  Ragnar Sigbj?rnsson  Carlo Giovanni Lai 《Bulletin of Earthquake Engineering》2011,9(4):931-953

Probabilistic seismic hazard analysis (PSHA) generally relies on the basic assumption that ground motion prediction equations (GMPEs) developed for other similar tectonic regions can be adopted in the considered area. This implies that observed ground motion and its variability at considered sites could be modelled by the selected GMPEs. Until now ground-motion variability has been taken into account in PSHA by integrating over the standard deviation reported in GMPEs, which significantly affects estimated ground motions, especially at very low probabilities of exceedance. To provide insight on this issue, ground-motion variability in the South Iceland Seismic Zone (SISZ), where many ground-motion records are available, is assessed. Three statistical methods are applied to separate the aleatory variability into source (inter-event), site (inter-site) and residual (intra-event and intra-site) components. Furthermore, the current PSHA procedure that makes the ergodic assumption of equality between spatially and temporal variability is examined. In contrast to the ergodic assumption, several recent studies show that the observed ground-motion variability at an individual location is lower than that implied by the standard deviation of a GMPE. This could imply a mishandling of aleatory uncertainty in PSHA by ignoring spatial variability and by mixing aleatory and epistemic uncertainties in the computation of sigma. Station correction coefficients are introduced in order to capture site effects at different stations. The introduction of the non-ergodic assumption in PSHA leads to larger epistemic uncertainty, although this is not the same as traditional epistemic uncertainty modelled using different GMPEs. The epistemic uncertainty due to the site correction coefficients (i.e. mean residuals) could be better constrained for future events if more information regarding the characteristics of these seismic sources and path dependence could be obtained.  相似文献   

Information Gathering in Bayesian Networks Applied to Petroleum Prospecting     

Marie Lilleborge  Ragnar Hauge  Jo Eidsvik 《Mathematical Geosciences》2016,48(3):233-257

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Platinum-group metals and their alloys in nuggets from alluvial deposits in Finnish Lapland     

Ragnar Trnroos  Yrj Vuorelainen 《Lithos》1987,20(6):491-500

Alluvial nuggets of PGE alloys from the rivers Miessijoki, Sotajoki, Puskuoja, Palsinoja and Ivalojoki at Kolmosenkoski rapids and from the Härkäselkä area have been investigated with a microprobe and a scanning electron microscope. Pt---Cu, Pd---Cu---Au and Os---Ir---Ru alloys occur as well as the main Pt---Fe alloys, both as inclusions in the Pt---Fe alloys and as separate nuggets or crystals. Limited optical properties are given. From the inclusions and associated minerals it is assumed that some of the nuggets are magmatic in origin and that others are a result of oxidative weathering. The material is rounded through transport, although the original euhedral form can often be observed.  相似文献   

Stochastic models for simulation of strong ground motion in Iceland     

Símon lafsson  Svein Remseth  Ragnar Sigbjrnsson 《地震工程与结构动力学》2001,30(9):1305-1331

Two types of modelling approaches for simulating ground motion in Iceland are studied and compared. The first type of models, named discrete‐time series models (ARMA), are based solely on measured acceleration in earthquakes occurring in Iceland. The second type of models are based on a theoretical seismic source model called the extended Brune model. Based on measured acceleration in Iceland during the period 1986–1996, the parameters for the extended Brune models have been estimated. The seismic source models are presented here as ARMA models, which simplifies the simulation process. A single‐layer soil amplification model is used in conjunction with the extended Brune model to estimate local site amplification. Emphasis is put on the ground motion models representing the variability in the measured earthquakes, with respect to energy, duration and frequency content. Demonstration is made using these models for constructing linear and non‐linear probabilistic response spectra using a discretised version of the Bouc–Wen model for the hysteresis of the second‐order system. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献