A triple porosity scheme for fluid/solid substitution: theory and experiment     

Yongyang Sun  Boris Gurevich  Maxim Lebedev  Stanislav Glubokovskikh  Vassili Mikhaltsevitch  Junxin Guo 《Geophysical Prospecting》2019,67(4):888-899

Quantifying the effects of pore-filling materials on elastic properties of porous rocks is of considerable interest in geophysical practice. For rocks saturated with fluids, the Gassmann equation is proved effective in estimating the exact change in seismic velocity or rock moduli upon the changes in properties of pore infill. For solid substance or viscoelastic materials, however, the Gassmann theory is not applicable as the rigidity of the pore fill (either elastic or viscoelastic) prevents pressure communication in the pore space, which is a key assumption of the Gassmann equation. In this paper, we explored the elastic properties of a sandstone sample saturated with fluid and solid substance under different confining pressures. This sandstone sample is saturated with octadecane, which is a hydrocarbon with a melting point of 28°C, making it convenient to use in the lab in both solid and fluid forms. Ultrasonically measured velocities of the dry rock exhibit strong pressure dependency, which is largely reduced for the filling of solid octadecane. Predictions by the Gassmann theory for the elastic moduli of the sandstone saturated with liquid octadecane are consistent with ultrasonic measurements, but underestimate the elastic moduli of the sandstone saturated with solid octadecane. Our analysis shows that the difference between the elastic moduli of the dry and solid-octadecane-saturated sandstone is controlled by the squirt flow between stiff, compliant, and the so-called intermediate pores (with an aspect ratio larger than that of compliant pore but much less than that of stiff pores). Therefore, we developed a triple porosity model to quantify the combined squirt flow effects of compliant and intermediate pores saturated with solid or viscoelastic infill. Full saturation of remaining stiff pores with solid or viscoelastic materials is then considered by the lower embedded bound theory. The proposed model gave a reasonable fit to the ultrasonic measurements of the elastic moduli of the sandstone saturated with liquid or solid octadecane. Comparison of the predictions by the new model to other solid substitution schemes implied that accounting for the combined effects of compliant and intermediate pores is necessary to explain the solid squirt effects.  相似文献   

Lagrangian study of temporal changes of a surface flow through the Kamchatka Strait     

Sergey V. Prants  Andrey G. Andreev  Michael Yu. Uleysky  Maxim V. Budyansky 《Ocean Dynamics》2014,64(6):771-780

Using Lagrangian methods, we analyze a 20-year-long estimate of water flux through the Kamchatka Strait in the northern North Pacific based on AVISO velocity field. It sheds new light on the flux pattern and its variability on annual and monthly time scales. Strong seasonality in surface outflow through the strait could be explained by temporal changes in the wind stress over the northern and western Bering Sea slopes. Interannual changes in a surface outflow through the Kamchatka Strait correlate significantly with the Near Strait inflow and Bering Strait outflow. Enhanced westward surface flow of the Alaskan Stream across the 174°E section in the northern North Pacific is accompanied by an increased inflow into the Bering Sea through the Near Strait. In summer, the surface flow pattern in the Kamchatka Strait is determined by the passage of anticyclonic and cyclonic mesoscale eddies. The wind stress over the Bering basin in winter–spring is responsible for eddy generation in the region.  相似文献   

Experimental estimation of velocities and anisotropy of a series of Swedish crystalline rocks and ores     

Alireza Malehmir  Magnus Andersson  Maxim Lebedev  Milovan Urosevic  Vassili Mikhaltsevitch 《Geophysical Prospecting》2013,61(1):153-167

To provide a guide for future deep (<1.5 km) seismic mineral exploration and to better understand the nature of reflections imaged by surface reflection seismic data in two mining camps and a carbonatite complex of Sweden, more than 50 rock and ore samples were collected and measured for their seismic velocities. The samples are geographically from the northern and central parts of Sweden, ranging from metallic ore deposits, meta‐volcanic and meta‐intrusive rocks to deformed and metamorphosed rocks. First, ultrasonic measurements of P‐ and S‐wave velocities at both atmospheric and elevated pressures, using 0.5 MHz P‐ and S‐wave transducers were conducted. The ultrasonic measurements suggest that most of the measured velocities show positive correlation with the density of the samples with an exception of a massive sulphide ore sample that shows significant low P‐ and S‐wave velocities. The low P‐ and S‐wave velocities are attributed to the mineral texture of the sample and partly lower pyrite content in comparison with a similar type sample obtained from Norway, which shows significantly higher P‐ and S‐wave velocities. Later, an iron ore sample from the central part of Sweden was measured using a low‐frequency (0.1–50 Hz) apparatus to provide comparison with the ultrasonic velocity measurements. The low‐frequency measurements indicate that the iron ore sample has minimal dispersion and attenuation. The iron ore sample shows the highest acoustic impedance among our samples suggesting that these deposits are favourable targets for seismic methods. This is further demonstrated by a real seismic section acquired over an iron ore mine in the central part of Sweden. Finally, a laser‐interferometer device was used to analyse elastic anisotropy of five rock samples taken from a major deformation zone in order to provide insights into the nature of reflections observed from the deformation zone. Up to 10% velocity‐anisotropy is estimated and demonstrated to be present for the samples taken from the deformation zone using the laser‐interferometery measurements. However, the origin of the reflections from the major deformation zone is attributed to a combination of anisotropy and amphibolite lenses within the deformation zone.  相似文献   

Magnetocentrifugal launching of jets from discs around Kerr black holes     

Maxim Lyutikov 《Monthly notices of the Royal Astronomical Society》2009,396(3):1545-1552

Strong magnetic fields modify particle motion in the curved space–time of spinning black holes and change the stability conditions of circular orbits. We study conditions for magnetocentrifugal jet launching from accretion discs around black holes, whereby large-scale black hole lines anchored in the disc may fling tenuous coronal gas outwards. For a Schwarzschild black hole, magnetocentrifugal launching requires that the poloidal component of magnetic fields makes an angle less than  60°  to the outward direction at the disc surface, similar to the Newtonian case. For prograde rotating discs around Kerr black holes, this angle increases and becomes  90°  for footpoints anchored to the disc near the horizon of a critically spinning   a = M   black hole. Thus, a disc around a critically spinning black hole may centrifugally launch a jet even along the rotation axis.  相似文献   

Centennial-to-millennial fluctuations in July temperatures in North Finland as recorded by timberline tree rings of Scots pine   总被引：1，自引：0，他引：1  

Maxim Ogurtsov  Markus Lindholm 《Quaternary Research》2005,63(2):182-188

A tree-ring proxy of summer temperature anomalies for northern Finland for the past 7500 yr was analyzed using Fourier spectrum and wavelet approaches. Multicentennial (250-450 yr) variability is present in the proxy record during most of the time range. This variability is suggested to reflect low-frequency variability in the North Atlantic Oscillation. Century-scale (90-130 yr) variation is another important feature of the tree-ring proxy data during the Holocene and may be attributed to Glessberg solar activity variations. In addition, an approximately 2000-yr quasi-period is found in this temperature proxy data, similar to the millennial-scale variability, present in many climate records from the North Atlantic region. The results point to the importance of multiple forcings underlying significant Holocene climatic fluctuations.  相似文献   

A step ahead of time: design, allocation and preservation of private open space in the 1920s––the case of a garden suburb in Israel     

Naftaly Goldshleger  Irit Amit-Cohen  Maxim Shoshany 《GeoJournal》2006,67(1):57-69

In the course of the last 50 years, the landscape in Israel has undergone major changes, due to accelerated urbanization following population growth. These processes had increased the pressure on the open land, especially in areas of urban expansion. Recognizing that Governments and local Municipalities had failed to stop the consequent loss of public open spaces, not only in Israel but worldwide, had lead recently many communities to adopt new solutions in the form of private open spaces. In this article we present a “step ahead of time”: a case of privately owned land, set aside as public green area during the 1920s in a neighborhood called “Ahuza Herbert Samuel” (Herbert Samuel, the first High Commissioner of Palestine under the British Mandate), located in the City of Haifa, in Northern Israel. The roots of this unique phenomenon during the 1920s could be linked to several sources of influence: Colonial town planning concepts, the emergence of garden cities and garden suburbs and most importantly to concepts brought in by the leaders of the immigrant community coming from Rumania. Photogrammetric and GIS analysis of this phenomenon had revealed that it had prevailed throughout 75 years of constant and massive increase in the demand for built-up areas in Israel in general and in Ahuza neighborhood in particular. The success in preserving these open areas gains current relevance in view of recent trends in the Western world of allocating privately owned green areas for public use.  相似文献   

Reconnaissance paleomagnetism of Late Triassic blocks, Kuyul region, Northern Kamchatka Peninsula, Russia     

William Harbert  Sergei Sokolov  Maxim Alexutin  Kirill Krylov  Vladimir Grigoriev  Alexander Heiphetz   《Tectonophysics》2003,361(3-4):215-227

The northernmost Kamchatka Peninsula is located along the northwestern margin of the Bering Sea and consists of complexly deformed accreted terranes. Progressing inland from the northwestern Bering Sea, the Olyutorskiy, Ukelayat and Koryak superterranes (OLY, UKL and KOR) are crossed. These terranes were accreted to the backstop Okhotsk-Chukotsk volcanic-plutonic belt (OChVB) in northernmost Kamchatka. A sedimentary sequence of Albian to Maastrichtian age overlaps the terranes and units of the Koryak superterrane, and constrains their accretion time. A paleomagnetic study of blocks within the Kuyul (KUY) terrane of the Koryak superterrane was completed at two localities (Camp 2: λ=61.83°N, φ=165.83°E and Camp 3: λ=61.67°N, φ=164.75°E). At both localities, paleomagnetic samples were collected from Late Triassic (225–208 Ma) limestone blocks (2–10 m in outcrop height) within a melange zone. Although weak in remanent magnetization, two components of remanent magnetization were observed during stepwise thermal demagnetization at 32 sites. The A component of magnetization was observed between room temperature and approximately 250 °C. This magnetic component is always of downward directed inclination and shows the best grouping at relatively low degrees of unfolding. Using McFadden–Reid inclination-only statistics and averaging all site means, the resulting A component mean is I_opt=60.3°, I₉₅=5.0° and n=36 (sites). The B magnetic component is observed up to 565 °C, at which temperature, most samples have no measurable remanent magnetization, or growth of magnetic minerals has disrupted the thermal demagnetization process. Combining sites with Fisher estimates of kappa (k-value)≥13 and n (sites)≥3, where bedding orientation differs within a block, most of these sites show the best grouping of B component directions at 100% unfolding, and two of the blocks display remanent magnetizations of both upward and downward directed magnetic inclination. Combining sites with Fisher estimates of kappa (k-value)≥13 and n (sites)≥3, the resulting overall B component paleolatitude and associated uncertainty are λ_obs=30.4°N or S, λ₉₅=8.9° and n=19 (sites). When compared with the expected North America paleolatitude of λ_{APWP expected}=57.9°N, our data support a model in which blocks within the Koryak superterrane are allochthonous and far travelled.  相似文献   

Tephra from andesitic Shiveluch volcano,Kamchatka, NW Pacific: chronology of explosive eruptions and geochemical fingerprinting of volcanic glass     

Vera Ponomareva  Maxim Portnyagin  Maria Pevzner  Maarten Blaauw  Philip Kyle  Alexander Derkachev 《International Journal of Earth Sciences》2015,104(5):1459-1482

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Looking into Pulsar Magnetospheres     

Maxim Lyutikov 《Astrophysics and Space Science》2001,278(1-2):81-84

Diffractive and refractive magnetospheric scintillations may allow direct probing of the plasma inside the pulsar light cylinder. The unusual electrodynamics of the strongly magnetized electron-positron plasma allows separation of the magnetospheric and interstellar scattering. The most distinctive feature of the magnetospheric scintillations is their independence of frequency. Diffractive scattering due to small scale inhomogeneities produces a scattering angle that may be as large as 0.1radians, and a typical decorrelation time of 10^-8 seconds. Refractive scattering due to large scale inhomogeneities is also possible, with atypical angle of 10^-3 radians and a correlation time of the order of10^-4 seconds. Some of the magnetospheric propagation effects may have already been observed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Gaussian beam imaging of walkaway VSP data based on finite differences in time domain     

Maxim I. Protasov  Maxim N. Dmitriev 《Computational Geosciences》2013,17(6):951-957

The approach to true amplitude seismic imaging for walkaway vertical seismic profile multicomponent data is presented and discussed. This approach is a migration procedure based on weighted summation of pre-stack data. True amplitude weights are computed with application of Gaussian beams. Gaussian beams are computed in time domain via finite-difference modeling. Numerical experiments with synthetic data generated for realistic salt model are presented and discussed.  相似文献