Thin Horizontal Plate Research Articles

Processing and interpretation of magnetic data in the Caucasus Mountains and the Caspian Sea: A review

<p>With the rapid development of aeromagnetic (primarily uncrewed) methods for measuring the magnetic field, the possibility of detailed magnetic research in hard-to-reach mountainous areas, forested areas, swamp areas, desert areas, and water areas has emerged. The conditions for interpreting the magnetic field are most difficult due to the vector nature of the magnetic properties of rocks, the wide range of their properties, and the presence of residual magnetization. The physical and geological conditions of the territory of Azerbaijan are characterized by rugged terrain relief, inclined magnetization (~58°), and complex geological environments. Along with using a probabilistic approach, deterministic methods for solving inverse and direct problems of geophysics become of great importance since it is possible to identify relatively extended reference boundaries and analyze magnetic anomalies from separate bodies of relatively simple shape. The article briefly outlines the main stages of processing and interpreting magnetic data under complex environments. The theoretical examples discussed include a block diagram of various disturbances, interpretive models of thin and thick beds, an intermediate model, a thin horizontal plate, and a horizontal circular cylinder on the flat and inclined surfaces under inclined magnetization conditions. The process of assessing magnetization on sloping terrain relief is shown. The presented field examples for the Caucasus Mountains show the quantitative interpretation of aeromagnetic data at the Big Somalit and Guton sites (southern Greater Caucasus, Azerbaijan), a deep regional profile through the Lesser and Greater Caucasus, magnetic field studies in the area around the Saatly superdeep borehole (Middle Kur depression between the Greater and Lesser Caucasus), and 3D magnetic field modeling at the Gyzylbulag gold deposit (the Azerbaijani part of the Lesser Caucasus). In the Caspian Sea, we demonstrated the use of an information parameter to identify faults in the Bulla hydrocarbon field (Gulf of Baku) and, for the first time, obtained the relationship between the generalized aeromagnetic data (2.5 kilometers over the mean sea level) and the central area of the mud volcanoes distribution in Azerbaijan.</p>

Characteristics of the Seismic Signal Generated by Fragmental Rockfalls: Insight From Laboratory Experiments

AbstractContinuous seismic signals are proposed as a useful quantitative information source for the estimation of rockfall properties. However, few studies have examined the characteristics of the seismic signal of fragmentation‐related rockfalls. In this study, a series of laboratory experiments designed with crushable analog blocks freefalling and impacting on a thin horizontal plate under different initial conditions (e.g., block volume, strength and fall height) were conducted. Strong correlations are observed between the rockfall properties and the seismic parameters when considering the rock fragmentation during impact. However, these relationships are observed only when the variation in potential energy spans over one order of magnitude, indicating that the application of seismic signals is limited by rockfall properties. In particular, the seismic energy calculated by the diffuse method is the most stable seismic parameter that is highly correlated with the potential energy of rockfalls. By compiling the available data of the seismic signals of both natural and experimental rockfalls from previous studies and our experiments, we found that the relationship between the seismic energy and the potential energy of rockfalls follows a power law model at all scales. The exponent of the power law function ranges from 1.11 to 1.69. Rock strength can significantly affect the seismic features, which are quantitatively discussed. Rock fragmentation acts as an intermediate variable, which is controlled by rockfall properties and consequently affects the corresponding seismic characteristics. Furthermore, rock fragmentation reduces the efficiency of the conversion of potential energy to seismic energy of rockfalls.

Rozensweig instability of two-layer system of immiscible ferrofluid

The stability of equilibrium for two-layer system of immiscible ferrofluids, separated by thin horizontal plate with a hole is considered. A numerical method for calculation of stability boundary in the space of dimensionless physical parameters of the system is proposed. In the case of circular hole the stability boundary and the most rapidly growing perturbations were calculated.

Quantitative interpretation of magnetic anomalies from bodies approximated by thick bed models in complex environments

Magnetic prospecting is a rapid and inexpensive geophysical tool and one of the most widely used methods for geophysical prospection throughout the world. However, the noise factors—such as inclined magnetization, complex geological structure of investigated areas, and uneven terrain relief—strongly obscure the interpretation of observed magnetic anomalies. The developed methodology of magnetic anomalies’ interpretation from models of thin beds and horizontal circular cylinders (spheres) in complex environments (oblique magnetization, rugged relief and unknown levels of the normal magnetic field) using improved versions of characteristic points and tangents was presented in detail in the author’s previous publications. However, many geological targets have a geometrical form of thick beds and thin horizontal plates and intermediate forms that crop up between these two models. In this paper, a methodology for interpreting magnetic anomalies produced by thick bed models in complex environments is explicitly described. It shows that quantitative analysis of magnetic anomalies due to intermediate targets could be successfully carried out using the methodology developed for the thick bed model. In the case of a thin horizontal plate with a large horizontal size, two distinct anomalies (from the left and right ends) may be interpreted as anomalies from thin beds. The interpretation methodology was successfully tested, both on typical models and on real geological targets. It was concluded that these methods could be effectively applied for quantitative analysis of magnetic surveys for geological–geophysical mapping, archeological target delineation, ore body searching, revealing oil and gas traps, and solving other geological and environmental problems.

Quantitative Interpretation of Magnetic Anomalies from Thick Bed, Horizontal Plate and Intermediate Models Under Complex Physical‐Geological Environments in Archaeological Prospection

AbstractMagnetic prospecting is one of the most widely used methods for archaeological prospection in the world. Noise both of natural [main factors are inclined magnetization, complex geological (archaeological) structure of investigated sites, and uneven terrain relief] and artificial origin (different iron‐containing targets, electric power lines, etc.) strongly obscure interpretation of observed magnetic anomalies. For quantitative analysis of magnetic anomalies produced by archaeological targets under aforementioned conditions a non‐conventional interpreting system has been developed. Methodology of magnetic anomalies interpretation from models of thin bed and horizontal circular cylinder (sphere) in conditions of oblique magnetization, rugged relief and unknown level of the total magnetic field by the use of improved versions of characteristic point and tangents has been earlier suggested. However, many archaeological targets have geometrical form of thick bed, thin horizontal plate and intermediate between these two models. In this paper methodology of magnetic anomalies produced by thick bed models in complex environments is explicitly described. It is shown that quantitative analysis of magnetic anomalies due to intermediate (between the thick bed and thin horizontal plate) targets could be successfully carried out by the use of methodology developed for the thick bed model. In the case of thin horizontal plate with a large horizontal extent, the two measured anomalies may be interpreted as anomalies from thin beds. The interpretation methodology was successfully tested both on typical models and on real archaeological targets with some success. Copyright © 2015 John Wiley & Sons, Ltd.

Wave forces on a submerged horizontal plate - Part I: Theory and modelling

This paper is concerned with the propagation of nonlinear gravity waves over a thin horizontal plate submerged in water of shallow depth. An unsteady solution of the problem is obtained by use of the theory of directed fluid-sheets for the two-dimensional motion of an incompressible and inviscid fluid. Particular attention is paid to the calculation of the nonlinear wave-induced vertical and horizontal forces and overturning moment by solving the Level I Green–Naghdi equations. The theoretical formulation of the problem is given in this paper (Part I), while the results due to solitary and cnoidal waves, and comparisons with the available experimental data are given in a companion paper under the same title (Part II).

Natural convective cooling of a horizontal heat conducting plate facing up in an otherwise adiabatic cavity

The transient conjugate cooling of a thin horizontal plate enclosed in an adiabatic cavity is studied using asymptotic and numerical techniques. The upper surface of the plate is in contact with a fluid initially at rest. The most important parameter to be obtained is the nondimensional cooling time, which depends on the aspect ratio of the plate ε, the nondimensional longitudinal heat conductance of the plate χ and the Prandtl number of the fluid Pr, for large values of the Rayeigh number of the laminar natural boundary layer flow induced by the density changes. Both the thermally thin ( α ⪢ ε 2) and thick wall regimes ( α ∼ ε 2) are considered in this paper. A minimum nondimensional cooling time is achieved for a thin plate (ε → 0) for values of the nondimensional longitudinal thermal conductance of the plate α, such as ε 2 ⪡ α ⪡ 1. That is, the process is faster if the longitudinal heat conduction through the wall is negligible.

Use of Reduced Sulfur Compounds by Beggiatoa spp.: Enzymology and Physiology of Marine and Freshwater Strains in Homogeneous and Gradient Cultures

The marine Beggiatoa strains MS-81-6 and MS-81-1c are filamentous, gliding, colorless sulfur bacteria. They have traditionally been cultured in very limited quantities in sulfide gradient media, where they grow as chemolithoautotrophs, forming a thin horizontal plate well below the air-agar interface. There, the facultatively chemolithoautotrophic strain MS-81-6 quantitatively harvests the flux of sulfide diffusing from below and oxidizes it to sulfate by using oxygen as the electron acceptor. Only recently have these strains been cultivated in bulk in defined liquid media (K. D. Hagen and D. C. Nelson, Appl. Environ. Microbiol. 62:947-953, 1996). In the current study, the obligately chemolithoautotrophic strain MS-81-1c was shown to have, despite much greater storage of elemental sulfur, an apparent Y(infH)(inf(inf2))(infS) twice that of MS-81-6 when the two strains were grown in identical sulfide-limited gradient media. While the basis of this difference in energy conservation has not been established, differences in sulfur oxidation enzymes were noted. Strain MS-81-1c appeared to be able to oxidize sulfite by using either the adenosine phosphosulfate (APS) pathway or a sulfite:acceptor oxidoreductase. APS pathway enzymes (ATP sulfurylase and APS reductase) were present at relatively high and constant levels regardless of growth conditions, while the sulfite:acceptor oxidoreductase activity varied at least eightfold, with the highest activity produced in sulfide gradient medium. By contrast, strain MS-81-6 showed no detectable activity of the APS pathway enzymes and possessed a sulfite:acceptor oxidoreductase activity just sufficient to account for its observed rate of growth in sulfide gradient medium. Freshwater strain OH-75-2a showed activity and regulation of sulfite:acceptor oxidoreductase consistent with lithotrophic energy conservation, a feature not yet proven for any freshwater Beggiatoa strain.

Laboratory experiments on the cloud-top entrainment instability

The stability of stratocumulus clouds with strong evaporative cooling effects is explored in laboratory simulations. Two fluids, initially separated by a thin horizontal plate, contain mixtures of water, alcohol and glycol which have a strongly nonlinear density as a function of mixture ratio. Initially, the fluid below the plate is more dense than that above the plate. When the plate is suddenly withdrawn, the turbulence in its wake mixes the two fluids together, producing mixtures with densities greater than that of either initial fluid. It is found that the system is unstable to strong perturbations only in cases of relatively large buoyancy reversal. The system is stable to strong perturbations if the buoyancy reversal is comparable to or less than the initial stratification. A simple model is presented to explain the results.

Magnetic anomalies over thin plates and their analysis

The magnetic anomaly over a two-dimensional thin horizontal plate is similar to the first horizontal derivative of the magnetic anomaly over a thick dipping dike of infinite depth extent but with a different direction of magnetization. Hence, the magnetic anomalies of thin plates may be integrated along the profile and the pseudomagnetic potential anomaly thus obtained may be interpreted using any standard method of interpreting dike anomalies. Expressions for the Fourier amplitude and phase spectra of the magnetic anomaly over a thin plate are also derived and procedures to evaluate the parameters of the plate from the spectra are formulated.

APPROXIMATION IN GRAVITY INTERPRETATION CALCULATIONS

Rigorous calculation of gravity effects of geologic bodies for the interpretation of subsurface structure from exploration gravity surveys is time‐consuming and tedious. Resort to electronic computers is convenient but not always necessary. Simple hand calculations can be instructive and are often adequate and useful. This paper reports the errors involved and ranges of validity of various simplifying approximations for commonly used geometric body shapes: (a) equivalent sphere approximation for an infinitely long horizontal cylinder, (b) circular plate approximation for horizontal slabs of finite width, (c) vertical line element and thin horizontal plate approximations for vertical cylinders of variable radii and heights (dome, salt dome, or plug), and (d) thin‐plate approximations for vertical dikes and horizontal fault blocks. The results are evaluated in terms of dimensionless parametric ratios, usually a characteristic dimension of the body versus depth to center of mass. Errors in the approximate calculations are remarkably small for several of the cases considered and the simplified results are valid for given precision over a rather large range of dimensions. For example, the maximum error in the thin‐plate approximation for an horizontal fault plate is less than one percent for a thickness/depth ratio ranging up to 0.75 which represents a very substantial fault throw. This particular example is more than adequate for most practical applications in geologic interpretations of gravity. On the other hand, some examples are shown to be unsuitable for simple approximation calculations.