Reflection and transmission responses of layered transversely isotropic viscoelastic media     

Alexey Stovas  Bjorn Ursin 《Geophysical Prospecting》2003,51(5):447-477

We consider a layered heterogeneous viscoelastic transversely isotropic medium with a vertical symmetry axis (a viscoelastic TIV medium) and parameters that depend on depth only. This takes into account intrinsic attenuation, anisotropy and thin layering. The seismic wavefield is decomposed into up- and downgoing waves scaled by the vertical energy flux. This scaling gives important symmetry relationships for both reflection and transmission (R/T) responses. For a stack of homogeneous layers, the exact reflection response can be computed in a numerically stable way by a simple layer-recursive algorithm. We derive exact plane-wave R/T coefficients and several linear and quadratic approximations between two viscoelastic TIV media, as functions of the real-valued horizontal slowness. The approximations are valid for pre- and post-critical values of horizontal slowness provided that the proper complex square roots are used when computing the vertical slowness. Numerical examples demonstrate that the quadratic approximations can be used for large differences in medium parameters, while the linear approximations can be used for small differences. For weak anisotropy it is sufficient to use an isotropic background medium, while for strong anisotropy it is necessary to use a weak TIV or TIV background medium. We also extend the O'Doherty–Anstey formula to the P- and SV-wave transmission responses of a stack of viscoelastic TIV layers, taking into account intrinsic attenuation, anisotropy and thin layering.  相似文献   

Evolution of Multipath Error Reduction with Signal Processing   总被引：1，自引：0，他引：1  

Zhdanov  Alexey  Zhodzishsky  Mark  Veitsel  Victor  Ashjaee  Javad 《GPS Solutions》2002,5(3):19-28

GPS Solutions - The described method of code and carrier multipath error reduction is a refinement of the strobe method of pseudo random noise (PRN) signal processing. This method utilizes as a...  相似文献   

Ray theory of modulated body waves in inhomogeneous viscoelastic media     

Alexey P. Kiselev 《Pure and Applied Geophysics》1993,140(4):629-640

Ray theory based upon real rays is presented for high frequencyP andS waves in continuously inhomogeneous isotropic linear media. Simple explicit formulae for the polarization anomalies described by higher order terms of the ray asymptotic expansions are considered.  相似文献   

The protolith nature of diamondiferous metamorphic rocks of the Kokchetav Massif     

Vladislav Shatsky  Emil Jagoutz  Olga Kozmenko  Alexey Ragozin  Sergei Skuzovatov  Nikolai Sobolev 《《地质学报》英文版》2018,92(Z1):173-173

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The Morcles microgranite (Aiguilles Rouges,Swiss Alps): geochronological and geochemical evidences for a common origin with the Vallorcine intrusion   总被引：1，自引：0，他引：1  

Denise Bussien Grosjean  Nicolas Meisser  Sylvie May-Leresche  Alexey Ulianov  Pierre Vonlanthen 《Swiss Journal of Geoscience》2018,111(1-2):35-49

The Morcles microgranite is located in the N–E termination of the Aiguilles Rouges massif (External Crystalline Massifs, Switzerland). It outcrops as dykes, a few meters to 150 m in thickness, intruding the Aiguilles Rouges polymetamorphic basement, and presents variation of texture from granophyric to rhyolitic. We present here for the first time, in situ U–Pb zircon dating of the Morcles microgranite/rhyolite based on laser-ablation—inductively coupled plasma—mass spectrometry (LA-ICP-MS) data. Results indicate late Variscan emplacement ages at ~303 and ~309–312 Ma, a major Caledonian inherited component age at ~445–460 Ma, and secondary inherited ages ranging from Pan-African (550–1000 Ma) to Paleoproterozoic (2.3 Ga). Geochronological and geochemical data indicate that the Morcles microgranite/rhyolite shares a common origin with the higher (or “H”) facies of the neighbouring Vallorcine granitic intrusion. This close affinity is further corroborated by the geographical alignment of both intrusive bodies on either side of the Rhone Valley. The fine-grained texture of the microgranite groundmass and the rhyolite indicates a very rapid cooling rate and emplacement close to the surface, suggesting that the Morcles microgranite/rhyolite may constitute the shallow-level counterpart of the Vallorcine granite. The mineralogical assemblages observed in the Morcles microgranite/rhyolite support the idea of high-temperature melting conditions provided by underplating of mantle-derived magmas during the Carboniferous extension of the Variscan cordillera.  相似文献   

Upper Mantle Density Heterogeneity in the European-Anatolian Tethys Belt     

Alexey SHULGIN  Irina M. ARTEMIEVA 《《地质学报》英文版》2021,95(Z1):9-10

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Investigating the Whole-lithosphere Structure of a Mineral System — Pathways and Source of Ore-forming Fluids Imaged with Magnetotelluric Modeling     

Matthew J. COMEAU  Michael BECKEN  Alexey V. KUVSHINOV  Sodnomsambuu DEMBEREL  Erdenechimeg BATMAGNAI  Shoovdor TSERENDUG 《《地质学报》英文版》2021,95(Z1):73-75

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Low-altitude geophysical magnetic prospecting based on multirotor UAV as a promising replacement for traditional ground survey     

Alexander V. Parshin  Vladimir A. Morozov  Anton V. Blinov  Alexey N. Kosterev  Alexander E. Budyak 《地球空间信息科学学报》2018,21(1):67-74

Abstract

The prospects for expanding the mineral resource base in many countries are linked with the exploration of stranded sites localized at unexplored areas with complex natural and landscape conditions that make any ground survey, including magnetic prospecting, difficult and expensive. The current level of geology requires high-precision and large-scale data at the first stages of geological exploration. Since 2012, technologies of aeromagnetic surveying with unmanned aircraft vehicles (UAV) enter the market, but most of them are based on big fixed-wing UAV and do not allow to substantially increase the level of survey granularity compared with traditional aerial methods. To increase the scale of survey, it is necessary to reduce the altitude and speed of flight, for which the authors develop the methodical and technical solutions described in this article. To obtain data at altitudes of 5 m above the terrain even in a rugged relief, we created heavy multirotor UAVs that are stable in flight and may be used in a wide range of environmental conditions (even a moderate snowfall), and develop a special software to generate flight missions on the basis of digital elevation models. A UAV has special design to reduce magnetic interference of the flight platform; the magnetic sensor is hung below the aircraft. This technology was conducted in a considerable amount of magnetic surveys in the mountainous regions of East Siberia between 2014 and 2016. The results of the comparison between airborne and ground surveys are presented, which show that the sensitivity of the developed system in conjunction with low-altitude measurements can cover any geologically significant anomalies of the magnetic field. An unmanned survey is cheaper and more productive; the multirotor-based technologies may largely replace traditional ground magnetic exploration in scales of 1:10,000?1:1000.  相似文献   

Atmospheric and Coupled Model Intercomparison in Terms of Amplitude Phase Characteristics of Surface Air Temperature Annual Cycle   总被引：1，自引：0，他引：1  

Alexey V. ELISEEV  Igor I. MOKHOV  Konstantin G. RUBINSTEIN  Maria S. GUSEVA 《大气科学进展》2004,21(6):837-847

A model intercomparison in terms of surface air temperature annual cycle ampitude-phase characteristics(SAT AC APC)is performed. The models included in the intercomparison belong to two groups:five atmospheric models with prescribed sea surface temperature and sea ice cover and four coupled models forced by the atmospheric abundances of anthropogenic consituents (in total six coupled model simulations). Over land, the models, simulating higher than observed time averaged SAT,also tend to simulate smaller than observed amplitude of its annual and semiannual harmonics and (outside the Tropics laterthan-observed spring and autumn moments. The models with larger(smaller) time averaged amplitudes of annual and semiannual harmonics also tend to simulate larger(smaller)interannual standard deviations. Over the oceans, the coupled models with larger interannual standard deviations of annual mean SAT tend to simulate larger interannual standard deviations of both annual and semiannual SAT harmonics amplitudes. Most model errors are located in the belts 60°-70°N and 60°-70°S and over Antarctica. These errors are larger for those coupled models which do not employ dynamical modules for sea ice.No systematic differences are found in the simulated time averaged fields of the surface air temperature annual cycle characteristics for atmospheric models on one hand and for the coupled models on the other. But the coupled models generally simulate interannual variability of SAT AC APC better than the atmospheric models (which tend to underestimate it). For the coupled models, the results are not very sensitive to the choice of the particular scenario of anthropogenic forcing.There is a strong linear positive relationship between the model simulated time averaged semiannual SAT harmonics amplitude and interannual standard deviation of annual mean SAT.It is stronger over the tropical oceans and is weaker in the extratropics. In the tropical oceanic areas, it is stronger for the coupled than for the atmospheric models.  相似文献   

Modelling of thermochemical plumes and implications for the origin of the Siberian traps     

Nickolay L. Dobretsov  Alexey A. Kirdyashkin  Anatoliy G. Kirdyashkin  Valery A. Vernikovsky  Igor N. Gladkov 《Lithos》2008,100(1-4):66-92

Thermochemical plumes form at the base of the lower mantle as a consequence of heat flow from the outer core and the presence of local chemical doping that decreases the melting temperature. Theoretical and experimental modelling of thermochemical plumes show that the diameter of a plume conduit remains practically constant during plume ascent. However, when the top of a plume reaches a refractory layer, whose melting temperature is higher than the melt temperature in the plume conduit, a mushroom-shaped plume head develops. Main parameters (melt viscosity, ascent time, ascent velocity, temperature differences in the plume conduit, and thermal power) are presented for a thermochemical plume ascending from the core–mantle boundary. In addition, the following relationships are developed: the pressure distribution in the plume conduit during the ascent of a plume, conditions for eruption-conduit formation, the effect of the P–T conditions and controls on the shape and size of a plume top, heat transfer between a thermochemical plume and the lithosphere (when the plume reaches the bottom of a refractory layer in the lithosphere), and eruption volume versus the time interval t₁ between plume formation and eruption. These relationships are used to determine thermal power and time t₁ for the Tunguska syneclise and the Siberian traps as a whole.

The Siberian and other trap provinces are characterized by giant volumes of lavas and sills formed a very short time period. Data permit a model for superplumes with three stages of formation: early (variable picrites and alkali basalts), main (tholeiite plateau basalts), and final (ultrabasic and alkaline lavas and intrusions). These stages reflect the evolution of a superplume from the ascent of one or several independent plumes, through the formation of thick lenses of mantle melts underplating the lithosphere and, finally, intrusion and extrusion of differentiated mantle melts. Synchronous syenite–granite intrusions and bimodal volcanism abundant in the margins of the Siberian traps are the result of melting of the lower crust at depths of 65–70 km under the effect of plume melts.  相似文献