A Neogene geomagnetic polarity transition record from lavas of the Canary Islands, Spain: episodic volcanism and/or metastable transitional fields?     

Jonathan M. G. Glen  Jean-Pierre Valet  Vicente Soler  Paul R. Renne  Agnès Elmaleh 《Geophysical Journal International》2003,154(2):426-440

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On long-period polar motion     

R. O. Vicente  C. R. Wilson 《Journal of Geodesy》2002,76(4):199-208

 Five separate polar motion series are examined in order to understand what portion of their variations at periods exceeding several years represents true polar motion. The data since the development of space-geodetic techniques (by themselves insufficient for study of long-period motion), and a variety of historical astrometric data sets, allow the following tentative conclusions: retrograde long-period polar motion below about −0.2 cpy (cycles per year) in pre-space-geodetic data (pre-1976) is dominantly noise. For 1976–1992, there is poor agreement between space-geodetic and astrometric series over the range −0.2 to +0.2 cpy, demonstrating that classical astrometry lacked the precision to monitor polar motion in this frequency range. It is concluded that all the pre-1976 astrometric polar motion data are likely to be dominated by noise at periods exceeding about 10 years. The exception to this is possibly a linear trend found in some astrometric and space geodetic series. At frequencies above prograde +0.2 cpy (periods shorter than about 5 years), historical astrometric data may be of sufficient quality for comparisons with geophysical excitation time series. Even in the era of space geodesy, significant differences are found in long-period variations in published polar motion time series. Received: 27 March 2001 / Accepted: 15 October 2001  相似文献   

Calorimetric study of the stability of high pressure phases in the systems CoOSiO₂ and “FeO”SiO₂, and calculation of phase diagrams in MOSiO₂ systems     

Alexandra Navrotsky  Faivel S. Pintchovski  Syun-Iti Akimoto 《Physics of the Earth and Planetary Interiors》1979,19(4):275-292

High temperature calorimetric measurements of the enthalpies of solution in molten if2 PbO · B₂O₃ of α- and γ-Fe₂SiO₄ and α-, β-, and γ-Co₂SiO₄ permit the calculation of phase relations at high pressure and temperature. The reported triple point involving α-, β-, and γ-Co₂SiO₄ is confirmed to represent stable equilibrium. The curvature in the α?β phase boundary in Co₂SiO₄ and of an α?γ boundary in Fe₂SiO₄ at high temperature is explained in part by the effects of compressibility and thermal expansion, but better agreement with the observed phase diagram is obtained when one considers the effect of small amounts of cation disorder in the spinel and/or modified spinel phases. The calculated ΔH⁰ and ΔS⁰ values for the α?β, α?γ, and β?γ transitions show that enthalpy and en changes both vary strongly in the series Mg, Fe, Co, and Ni, and are of equal importance in determining the stability relations. The disproportionation of Fe₂SiO₄ and Co₂SiO₄ spinel to rocksalt plus stishovite is calculated to occur in the 170–190 kbar region; cation disorder and/or changes in wüstite stoichiometry can affect the P?T slope. The calorimetric data for CoSiO₃ and FeSiO₃ are in good agreement with the observed phase boundary for pyroxene formation from olivine and quartz. The decomposition of pyroxene to spinel and stishovite at pressures near the coesite-stishovite transition is predicted in both iron and cobalt systems. The use of calorimetric data, obtained from small samples of high pressure phases, is very useful in predicting equilibrium phase diagrams in the 50–300 kbar range.  相似文献   

Medieval Macrospace Through GIS: The Norse World Project Approach     

Alexandra Petrulevich  Agnieszka Backman  Jonathan Adams 《The Cartographic journal》2020,57(1):18-27

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Tides in the English Channel and Southern North Sea. A frequency domain analysis using model TEA-NL     

Antnio M. Baptista  Joannes J. Westerink  Paul J. Turner 《Advances in water resources》1989,12(4)

The frequency-time finite element model TEA-NL is used to investigate tidal propagation and circulation in the English Channel and the southern North Sea, in the context of the Tidal Flow Forum benchmark. Quality of TEA-NL simulations, relative to both field data and simulations by other numerical models is discussed. Sensitivity analyses are performed with regard to the effect on accuracy of bottom friction, and the effect on computational cost of the strategy used to harmonically decompose and iterate non-linear loading terms in the shallow water equations.  相似文献   

Thermochemistry of the new silica polymorph moganite     

Ivan Petrovic  Peter J. Heaney  Alexandra Navrotsky 《Physics and Chemistry of Minerals》1996,23(2):119-126

Samples of microcrystalline silica varieties containing variable amounts of the new silica polymorph moganite (up to R~82 wt.%) have been studied by a combination of high temperature solution calorimetry using lead borate (2 PbO · B₂O₃) solvent and transposed temperature drop calorimetry near 977 K, in order to investigate the thermochemical stability of this new silica mineral. The enthalpy of solution at 977 K and the heat content (H₉₇₇ — H₂₉₈) of “pure” moganite phase were estimated to be -7.16 ± 0.35 kJ/mol and 43.62 ± 0.50 kJ/mol, respectively. The standard molar enthalpy of formation is-907.3 ± 1.2 kJ/mol. Thus, calorimetry strongly supports results of previous X-ray and Raman spectroscopic studies that moganite is a distinct silica polymorph. Its thermochemical instability relative to quartz at 298 K of 3.4 ± 0.7 kJ/mol is marginally higher than those of cristobalite and tridymite. Structurally, this instability may be related to the presence of distorted 4-membered rings of SiO₄ tetrahedra, which are not found in the quartz structure. The metastability relative to quartz may also explain the apparent scarcity of moganite in altered rocks and in rocks that are older than 130 my.  相似文献   

The effect of Fe on the crystal structure of wadsleyite β-(Mg1 − x Fe x )2SiO4, 0.00≤x≤0.40     

Larry W. Finger  Robert M. Hazen  Jinmin Zhang  Jaidong Ko  Alexandra Navrotsky 《Physics and Chemistry of Minerals》1993,19(6):361-368

Single crystals of five wadsleyite compositions, β-(Mg,Fe)₂SiO₄ with Fe/(Fe+Mg)=0.00, 0.08, 0.16, 0.25 and 0.40, have been synthesized at high temperature and pressure in a uniaxial, split-sphere apparatus. Crystal structures of these samples, determined by x-ray diffraction techniques, reveal that iron is significantly ordered: Fe is depleted in the M2 octahedron, while it is enriched in M1 and M3. The most iron-rich synthetic sample, which falls well outside previous estimates of wadsleyite stability, raises questions regarding published Mg₂SiO₄-Fe₂SiO₄ phase diagrams at transition zone conditions.  相似文献   

Solar variability and climate     

Sabatino Sofia  Peter Fox 《Climatic change》1994,27(3):249-257

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Nota sobre la profundidad hipocentral del sismo del apenino toscano-romañol de 11 de febrero de 1939     

Ing. Vicente Inglada 《Pure and Applied Geophysics》1948,12(5-6):181-188

Resumen En la presente Nota se determina por el método deKöveslighèty, valiéndose de fórmulas especiales y una variante que simplifica el cálculo extraordinariamente, la profundidad del sismo del Apenino toscano-romañol de 11 de febrero de 1939. Se obtiene para ella el valorh=6871 metros, que está en muy buen acuerdo con los dos de 7 y 10 km, obtenidos por el Prof.P. Caloi, valiéndose de los sismogramas registrados en las Estaciones próximas. Al final se hecen algunas consideraciones acerca de las ventajas, que, en ciertos casos, ofrece dicho metodo.Esta Nota va dedicada, como prueba de gran consideración y afecto, a nuestro querido amigo e ilustre Sismólogo Dr.G. Agamennone, con ocasión del homenaje que se le tributa en su 90° aniversario.  相似文献   

Identification of potential subsidence related to pumping in the Almería basin (SE Spain)     

Antonio Pulido‐Bosch  José Delgado  Fernando Sola  Ángela Vallejos  Fernando Vicente  Juan M. López‐Sánchez  Jordi J. Mallorquí 《水文研究》2012,26(5):731-740

Ground subsidence of detrital deposits in the Almería basin (SE Spain) was studied using the remote sensing technique of Differential Interferometry SAR (DInSAR). This basin is one of the most arid in Europe, receiving an average rainfall of 250 mm per year. Over the last 60 years the region has experienced an enormous agricultural and urban expansion, whose water demand has been largely supplied from groundwater, leading to the current situation of overexploitation of water resources. This paper outlines the likely relationship between groundwater abstraction and subsidence. To this end, 34 ERS and Envisat images, taken between 2003 and 2009, were analysed to estimate ground surface deformations, and hence, compared with water table variations measured in a number of piezometers in the basin. The analysis shows a clear parallelism between the variations in piezometric level and deformation of the ground surface. In addition, the zones of greatest subsidence coincide with those areas where groundwater abstractions are concentrated. Subsidence over the examined period varies from 10 to 30 mm, with extreme values as high as 50 mm, which translates to a rate of between 1·7 and 5 mm/year, reaching maximum rates of 8 mm/year at some points. Given such subsidence rates, damage to urban infrastructures are, for the moment, incipient. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献