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1.
Cataclasis and processes of particle size reduction   总被引：6，自引：0，他引：6  
The particle size distribution (P.S.D.) of fragmented geological materials is affected by the fragmentation process, initial size distribution, number of fracturing events, energy input, strain, and confining pressure. A summary of literature shows that the fractal dimension (D) of the P.S.D. is increased by the number of fracturing events, energy input, strain, and confining pressure. Cenozoic cataclasis of granite, granodiorites, gneisses and arkose seen in cores from the Cajon Pass drillhole, southern California, produced P.S.D.s with values ofD that varied from 1.88 to 3.08. Each rock type has a characteristic and more limited range ofD. Areas of dilatant texture and modeI fracture-fillings have low average values (2.32 and 2.37) compared to an average value of 2.67 in shear fracture-fillingsD has a good inverse correlation with average particle size. Data from fault rocks in the San Gabriel fault zone, southern California (Anderson et al., 1983) have been reanalyzed to show that values ofD are higher (2.10–5.52) and average particle size is lower than the Cajon Pass samples, but the ranges of values overlap, and the inverse correlation betweenD and average particle size is extended. Microstructural observations combined with these results suggest that three processes contributed to particle size reduction during cataclasis. The first process of feldspar alteration, which leads to low values ofD, has not been previously recognized. The second process is probably constrained comminution (Sammis et al., 1987), since the averageD in shear fracture-fillings is close to the value of 2.58 predicted by this theory. A further stage of particle size reduction is demonstrated by an increase ofD with cataclasis. This third process is selective fracture of larger particles, which may also operate during localization and the cataclastic flow-to-faulting transition as observed in experiments. A transition from constrained comminution to selective fracture of large particles, and increasingD values with cataclastic evolution and grain size reduction, may be general features of experimental and natural cataclasis.  相似文献   

2.
Summary A new parameter-equivalent electron density (N ae)—has been introduced for evaluating the ionospheric condition inD region and the quantitative relations for its determination has been deduced. The new parameter is a function of the absorption and can be determined from a measurement point by a single frequency either by vertical incidence sounding or by registering the field strength for CW transmitter in a frequency range of 0.6–3 mc/s. The equivalent electron density presents a more objective information about the physical condition ofD region in comparison with the absorption itself and proves to be a suitable parameter for the study of the time variations of the ionisation conditions ofD region.  相似文献   

3.
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4.
The magnetic anomaly due to a long tabular body usually consists of a maximum and a minimum. The distances and the amplitudes of the maximum and the minimum, when defined in dimensionless quantities, may be used as characteristics of the source. In this paper, a method based on the positions of the maximum and the minimum on the magnetic anomaly due to a long tabular body has been presented. Characteristic ratios,D andA involving the distances and amplitudes of the maximum and the minimum points on the anomaly curve are defined. Nomograms showing the variations ofD andA with the parameters of (1) the dike and (2) the vertical fault models are presented. The parameters of the causative source are evaluated from the two ratiosD andA and the nomograms, using some simple analytical relations presented here. From the nomograms, it is observed that (a) for a thick dike,A is always greater thanD, (b)A=D for a thin sheet and (c) for a vertical fault,A is always less thanD. Thus from the characteristic ratiosD andA it is possible to evaluate the source parameters and also to distinguish whether the source is a dike, sheet or a vertical fault. The method is fast and is applicable for the magnetic anomalies either in total, vertical or horizontal component. The method has been applied on two field examples and the results are found to be in close agreement with those obtained by using other methods. A simple method of locating the origin on the anomaly curve is included. The limitations of the method are also discussed.  相似文献   

5.
Summary Evidence is adduced indicating that geomagnetic disturbance at Huancayo isnormal, that is, comparable with that shown elsewhere in similar latitudes —as contrasted with the remarkable Huancayoabnormality, in the horizontal magnetic force, of the quiet-day solar and lunar daily variations, and in theS q augmentation (solar flare effect). the normality of magnetic disturbance at Huancayo is manifested by the disturbance daily variationS D, and by the storm-effectD st and its associated changes of daily mean (D m) and the non-cyclic variation; it is not stated whether or not the irregular part,D i, is normal. The normality ofD st seems natural according to theChapman-Ferraro theory of magnetic storms, but the normality ofS D is less easy to explain.Prof.Sydney Chapman, Research Associate, California Institute of Technology, under Signal Corps Project No. 24-172 B; on leave (from April 1950 to March 1951) from Oxford University, Queen's College,Oxford, England.  相似文献   

6.
Abstract

An idealized nonlinear αω-dynamo is investigated. Emphasis is placed upon the different spatial symmetries, and the asymmetries that arise after secondary bifurcations. On varying the main control parameter D (the dynamo number), many transitions are found involving solutions without an equatorial symmetry, and solutions with quasiperiodic time dependence, but no chaos. Instead of a cascade to smaller spatial scales when D is highly supercritical it is found that additional asymmetries are introduced at tertiary bifurcations. Our complete bifurcation diagrams allow us to follow in detail how stability is passed from one solution to another as D varies. In these diagrams there are typically multiple stable solutions at any value of D, which suggests that similar stars can have different magnetic patterns.  相似文献   

7.
A review of modern dynamic models of the Earth’s magnetosphere (the A2000 paraboloid model and Tsyganenko’s T01 model) is presented. For the magnetic storm of January 9–11, 1997, the results of joint calculations of the magnetospheric magnetic field are presented and contributions of the large-scale magnetospheric currents to the D st variations are analyzed. Both models were shown to be well consistent with measurement data; the contribution of the magnetotail current system to D st is comparable to the contribution of the ring current. At the same time, the relative dynamics of magnetospheric current systems are different in different models. The differences in the magnetic field variation profiles for various current systems calculated by the A2000 and T01 models are explained by model parameterizations.  相似文献   

8.
Summary TheWiechert-Herglotz method to investigate seismically the Earth structure, is adapted for refraction prospecting. The case of a single layer bounded by a sloping interface is considered. The velocity is assumed to be an increasing function of depth within the layer and constant beneath. A general procedure of computation is outlined. Special formulae are given in addition for the case in which the dromochroneD 1 corresponding to disturbances propagated only through the layer are of parabolic shape. Table I was calculated using them and assuming an horizontal interface. It may be seen there that valuesh 1 of the layer thickness furnished by these formulae may become considerably greater than those based on D1 rectilinear. Computation ofh 1 may easily be performed by means of the same table.  相似文献   

9.
Abstract

The flow of a rotating homogeneous, incompressible fluid past a long ridge is investigated. An analysis is presented for flows in which E ? 1, Ro ～ E½, H/D ～ E0, h/D ～ E½ and cosα ～ E0 where E is the Ekman number, Ro the Rossby number, H/D the fluid depth to ridge width ratio, h/D the ridge height to ridge width ratio and α the angle between the free stream flow and a line perpendicular to the ridge axis. The analysis includes effects of the nonlinear inertial terms. Particular examples of a ridge of triangular cross section and a sinusoidal topography are investigated in some detail. Experiments are presented for a triangular ridge which are in good agreement with the theory.  相似文献   

10.
The paper deals with the mechanical origin and rules ofen echelon folds and their secondary fractures by means of elastic stability theory and nonlinear fracture criterion. Obtains the quantitative relations amongen echelon angles ofen echelon folds, ratios of boundary stresses anden echelon pitches of shear zone under an action of general boundary forces (tension shear, pure shear or compression shear). As an applied example, the paper researches the displacement field, stress field, distortion energy distribution, state of secondary fractures and energy released by fracturing ofen echelon fold structure developed at the east foot of Taihang Mountain. The results of research show that maximum principal (compressive) stresses, maximum shear stresses, high value area of distortion energy are in the nuclear parts ofen echelon folds. In these parts compressive fractures were easily developed in approximately parallel with fold axis. So it is verified that the secondary fracture ofen echelon folds is a mechanism controlling a strong earthquake.  相似文献   

11.
Summary In Paper III (Mohandis [1]2) we considered the sudden introduction of amagnetic dipole in the earth's core to act as a source of disturbance to the exitation field taken as a poloidal one. A symmetrical case was considered where the dipole axis is placed parallel to the original field and perpendicular to the earth's mantle. In the present work, we consider an unsymmetric case where the axis of themagnetic dipole is placed perpendicular to both the mantle and the exitation field which is taken as a toroidal one. A mathematical study is made for the resulting fluid motion in the core as well as for the generated hydromagnetic perturbations in both the mantle and the earth's fluid core. A more powerful method has been adopted than those used in previous cases.  相似文献   

12.
An actinometric method to determine the rate constantk 1D of O(1D) formation by ozone photolysis in the troposphere and at higher altitudes is presented. N2O is used as a scavenger gas for O(1D), and the molecular nitrogen product measured after gas chromatographic separation. First results of the method for ground level and for 26 km altitude are reported and compared with theoretical estimates ofk 1D for these levels.  相似文献   

13.
Multifractal analysis of earthquakes   总被引：5，自引：0，他引：5  
Multifractal properties of the epicenter and hypocenter distribution and also of the energy distribution of earthquakes are studied for California, Japan, and Greece. The calculatedD q-q curves (the generalized dimension) indicate that the earthquake process is multifractal or heterogeneous in the fractal dimension. Japanese earthquakes are the most heterogeneous and Californian earthquakes are the least. Since the earthquake process is multifractal, a single value of the so-called fractal dimension is not sufficient to characterize the earthquake process. Studies of multifractal models of earthquakes are recommended. Temporal changes of theD q-q curve are also obtained for Californian and Japanese earthquakes. TheD q-q curve shows two distinctly different types in each region; the gentle type and the steep type. The steeptype corresponds to a strongly heterogeneous multifractal, which appears during seismically active periods when large earthquakes occur.D q for smallq or negativeq is considerably more sensitive to the change in fractal structure of earthquakes thanD q forq2. We recommend use ofD q at smallq to detect the seismicity change in a local area.  相似文献   

14.
Abstract

We discuss the steady states of the αω-dynamo in a thin disc which arise due to α-quenching. Two asymptotic regimes are considered, one for the dynamo numberD near the generation thresholdD 0, and the other for |D| ? 1. Asymptotic solutions for |D—D 0| ? |D 0| have a rather universal character provided only that the bifurcation is supercritical. For |D| ? 1 the asymptotic solution crucially depends on whether or not the mean helicity α, as a function ofB, has a positive root (hereB is the mean magnetic field). When such a root exists, the field value in the major portion of the disc is O(l), while near the disc surface thin boundary layers appear where the field rapidly decreases to zero (if the disc is surrounded by vacuum). Otherwise, when α = O(|B|?s) for |B| → ∞, we demonstrate that |B| = O(|D|1/s ) and the solution is free of boundary layers. The results obtained here admit direct comparison with observations of magnetic fields in spiral galaxies, so that an appropriate model of nonlinear galactic dynamos hopefully could be specified.  相似文献   

15.
Supposing that the distribution of scatterers in a three-dimensional medium is not uniform but fractally homogeneous with fractal dimensionD, we have made the dimensional analysis for the temporal decay of the multiple scattering energy density at the hypocenter.The number of scatters in a sphere of radiusR is assumed to be proportional toR D . Then, the energy density of thekth order scattering decays according to the [(D–2)k–3]th power of lapse time. A fractal dimension ofD=3 corresponds to the uniform distribution. If 2<D3, multiple scattering terms of orderk2 dominate over the single scattering term (k=1) at long lapse time. IfD=2, energy density of every order decays according to the — 3rd power of lapse time. The single scattering model survives on conditionD<2; the single scattering term dominates over the higher order multiple scattering terms even at long lapse time, since the negative power of lapse time fork=1 is the smallest of all.  相似文献   

16.
Zusammenfassung Die magnetischen Bais werden in zwei Klassen (I und II) eingeteilt, je nachdem sie positive oder negative Ausschlagsrichtung inH zeigen. Wie die Analysen der charakteristischen Hauptstromvektoren ergeben, kann man aus dem Verhalten derH-Variationen allein nichts über den tatsächlichen Verlauf des ionosphärischen Strombandes aussagen. Da dieD-Variationen größenordnungsmäßig denH-Variationen entsprechen, gewinnt man erst nach Berücksichtigung beider Elemente ein sicheres Bild der Stromverhältnisse. So können bei ähnlichenD-Schwankungen aber entgegengesetzten Ausschlägen inH fast gleiche Stromverhältnisse in der Ionosphäre existieren. — Bemerkenswert ist bei sehr vielen Bais das Einsetzen desD-Maximums vor dem desH-Maximums. Das entspricht einer anfänglich meridionalen Strömung, die allmählich in eine zonale einbiegt.
Summary The magnetic bays are divided into two classes according to their positive or negative directions ofH. As results from the analysis the characteristic main-current-vectors nothing definitive can be concluded from the behavior of theH-variations alone concerning the actual course of the ionospheric ribbon-current. Since theD-variations in their sizes correspond with theH-variations a correct picture of the positions can be only won after considerations of eather element. Thus almost similar current situations may exist in the ionosphere provided similarD-fluctuations showing different directions inH are effective. — Particularly to be mentioned is the fact that in many bays the maximum appears before that of theH-maximum and this is corresponding to the initial meridional-current which slowly turns into a zonalcurrent.
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17.
This study concludes that the elongation axis (K 1) of the ellipsoid of anisotropic magnetic susceptibility (AMS) is a suitable proxy for flow axis in ashflow tuffs. 153 oriented samples (176 specimens) were studied from 18 sites in the 1.1 Ma Tshirege member of the Bandelier Tuff. These sites are distributed around the Valles caldera at distances of 5–25 km outside of the rim.K 1 axes correlate well with postulated radial flow axes at 13 sites.K 1 also agrees with measured geological flow indicators, mainly imbricated larger clasts, at 7 sites. At 2 of the 5 sites where significant disagreement is seen between theoretical radial flow directions and measuredK 1 axes, theK 1 axes correspond well with geological flow indicators, indicating that the divergence of flow from the predicted radial flow pattern is real. Two major topographic buttresses are suggested as the cause of flow divergence for the Tshirege ash flows: the San Pedro buttress northwest of the caldera, and the San Miguel buttress in the southeast. In situK 1 axes plunge about 7° toward the source at two-thirds of the sites; therefore the plunge ofK 1 is a plausible in situ indicator for thedirection of flow. Multiple flow zones in sections of several meters thickness indicate changes of flow direction that are both rapid and large during ash-flow emplacement. These observations raisre the question of how best to represent mean flow directions in ash-flow sheets: by eigenvector methods, by vector-sum methods, or by modes. A method for measuring imbrication of larger clasts using apparent dips in vertical joints is outlined. Imbrication, determined in this way at one-third of the sites, dips toward the source, i.e., up-flow. The minimum (K 3) axis of the AMS ellipsoid correlates with the flow foliation rather than with the larger clast imbrication. The flow axes of ash flows correspond with theK 1 axes, not with the declination ofK 3 axes as suggested by some authors. Initial dip of the sampled ash flows is not large and does not affect the paleomagnetic remanence direction, which is reversed with a mean ofD=173.5°,I=-38.4°, 95=3.4°N=18. This mean is not different at the 95% confidence level from that of earlier workers. The mean pole, at 098.0°E, 74.8°N,A 95=3.3°,N=18, is about 15° far-sided relative to the expected time-averaged geomagnetic pole, suggesting a history of emplacement too short to adequately average secular variation.  相似文献   

18.
If the magnetic vertical intensityZ is known over a certain area, it is possible, under more precisely defined conditions which are often complied with, at arbitrary points of the same area—though with the exception of the marginal area—to calculate the deviations of the horizontal intensityH and the magnetic declinationD, H and D, from constant values. Below some details of the calculation in practice are given, i. a. by means of an example, the mathematic basis for the calculations being outlined in the introduction (the succeeding text may, however, be read independently thereof). A graticule, as seen in Fig. 1, was used in the calculations, and the method itself is described under «2. Procedure». In Figs. 2 and 3, the figures at the crosses denote the values ofH andD computed in this way, indicated in gammas and arc-minutes, respectively; (the isomagneticH-lines in Fig. 2 are drawn on the basis ofobserved H-values; in Fig. 3 the observedD0values themselves are given in figures in small type). The accuracy of and the possibilities for application of the method are discussed in the later sections.
Zusammenfassung Wenn man die magnetische Vertikalintensität in einem Gebiet kennt, ist es unter gewissen Bedingungen, die oft erfüllt sind, möglich in willkürlich gewählten Punkten des Gebietes — mit Ausnahme des Randgebietes — die Abweichungen H und D der HorizontalintensitätH und der DeklinationD von konstanten Werten zu berechnen. Weiter unten sind Einzelheiten der praktischen Ausführung anhand eines Beispiels mitgeteilt. Die mathematische Grundlage der Berechnungen ist in der Einleitung skizziert; doch können die folgenden Abschnitte auch unabhängig von ihn verstanden werden. Für die Berechnungen wurde ein, Integrationsgitter (Abb. 1) verwendet, und die Methode selber ist unter «2. Procedure» beschrieben. In Abb. 2 und 3 zeigen die Zahlen bei den Kreuze die in dieser Weise berechneten Werte vonH undD, angegeben in Gammawerten und Bogenminuten; (die isomagnetischen Linien in Abb. 2 sind auf Grund vonbeobachteten H-Werten gezeichnet worden; in Abb. 3 sind die beobachtetenD-Werte in kleiner Typen gedruckt). In den Abschnitten 3 und 4 werden die Genauigkeit und die Anwendungsmöglichkeiten der Methode diskutiert.
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19.
The diurnal variations in the amplitude and parameters of polarization ellipses of the first Schumann resonance according to three magnetic field components, observed on December 1–10, 2007, at the Barentsburg and Lovozero observatories, have been studied. Ellipses have been constructed in the (H, D) and (H, Z) planes. The value of the minor axis, inclination of the major axis, ellipticity, and the rotation direction have been estimated. The vertical magnetic component of the Schumann resonance is three to four times as small as the horizontal component. The difference in the diurnal variations in the ellipse parameters between both observatories has been found. The effect can be caused by a difference in the Earth’s conductivity in the vicinity of the observatories and by conductivity anisotropy. The major axis inclination and ellipticity have semidiurnal components. The polarization vector mostly rotates from D to H in the horizontal plane and from Z to H in the vertical plane at both stations.  相似文献   

20.
The decrease in density contrast of sedimentary rocks with depth in many sedimentary basins can be approximated by a parabolic density function. Analytical gravity expression of an outcropping two-dimensional vertical step along which the density contrast decreases parabolically with depth is derived in the space domain. A modification ofBott's (1960) method of gravity interpretation is proposed by considering two outcropping vertical steps on either side of the first and last observation points in addition toN outcropping vertical prisms in order to interpret the gravity anomalies of nonoutcropping basins. The thicknesses of the two outcropping vertical steps are made equal to the thicknesses of the two outcropping vertical prisms placed below the first and last observation points. The initial depth estimates of the sedimentary basin are calculated by the infinite slab formula ofVisweswara Rao et al. (1993). The gravity effects of theN outcropping prisms and the two outcropping vertical steps are calculated at each anomaly point and the depth to the floor of the basin are adjusted based on the differences between the observed and calculated anomalies. A gravity anomaly profile of Los Angeles basin, California is interpreted.  相似文献   

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