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1.
B. T. Brady 《Pure and Applied Geophysics》1976,114(4):727-739
The scale invariant inclusion theory of failure is applied to the problem of aftershock sequences. In the inclusion theory, a macrocrack, or void of low aspect ratio, the length of which depends upon the magnitude of the impending mainshock, forms within the inclusion zone of the impending earthquake. The fault zone that precedes the inclusion zone represents that part of the macrocrack that has closed. It is shown that bifurcation (branching) of the macrocrack and its associated fault must occur within the focal region of the inclusion during the growth phase of the earthquake. The bifurcation process produces extensive faulting of the material that comprises the focal region.A prediction of the inclusion theory is that each fault within the focal region will terminate within a zone of concentrated dilatancy that may or may not be in an unstable state. When the zone is unstable, an aftershock will occur. It is shown that these inclusion zones will, on the average, occur near the boundaries of the focal region. Failure of these unstable zones leads to additional failures within the interior portions of the focal region. These failures represent lock point failures along the fault(s) and will, in general, exhibit few or no additional aftershocks.The bifurcation model of aftershock sequences leads to five results: (1) The aftershock sequence will exhibit an inverse hyperbolic time decay law when the stresses that are applied at distances far removed from the hypocenter remain constant during the sequence and when there isno interaction between the brittle lithosphere (where aftershocks occur) and the underlying asthenosphere. (2) The mean magnitude of any group of aftershocks within the sequence will be approximately constant in time. (3) The aftershocks will, in general, have focal mechanisms identical to that of the mainshock. (4) Large seismic events that occur throughout the aftershock zone will be independent of one another when the aftershocks are sufficiently far apart (two-three fault lengths) and when the applied tectonic stresses remain constant during the sequence. (5) The bifurcation model predicts that theb-value of the aftershock sequence will be 1.0 when both the Utsu relationship between aftershock area and mainshock magnitude and the Gutenburg Richter frequency-magnitude relationship are satisfied. 相似文献
2.
Recent investigations of magnetospheric plasma structure are summarized under the broad categories of empirical models, transport across boundaries, formation, and dynamics of the plasma sheet. This report reviews work in these areas during the period 1991 to 1993. Fully three-dimensional empirical models and simulations have become important contributors to our understanding of the magnetospheric system. Some new structural concepts have appeared in the literature: the entry boundary and geopause, the plasma sheet region 1 vortices, the low-energy layer, the adiabaticity boundary or wall region, and a region in the tail to which we refer as the injection port. Traditional structural concepts have also been the subject of recent study, notably the plasmapause, the magnetopause, and the plasma sheet. Significant progress has been made in understanding the nature of plasma sheet formation and dynamics, but the acceleration of electrons to high energy remains somewhat mysterious. 相似文献
3.
aam mam uu mn¶rt;muaamuu n¶rt; u u nua ua —aam auumu m mnam (200–1000°, 2 10–1 a). aa¶rt;u, m um na¶rt;a uu a n¶rt;u auumu mn¶rt;mu m mnam, u¶rt;m auumu ¶rt;a mn¶rt;mu mnam u n¶rt;m mu mnam uma. 相似文献
4.
V. S. Mingalev V. N. Krivilev M. L. Yevlashina G. I. Mingaleva 《Pure and Applied Geophysics》1988,127(2-3):323-334
The results of a detailed numerical study of the behaviour of the convective polar ionosphere are presented. The developed theoretical model produces three-dimensional distribution of electron density, electron and ion temperature. The effects of auroral particle precipitation on the density and temperature structures are studied for winter and low solar activity conditions. The high-latitude ionospheric features, such as the tongue of ionization, the main trough the polar ionization peak, the auroral ionization peak, the high-latitude ionization hole, the tongue of electron temperature, the high latitude minima of electron, temperature, and the ion temperature hot spot are obtained from calculations.Numerically obtained results are used for determining the HF propagation paths in the polar ionosphere. The effects of ionospheric irregularities on high frequency ionospheric radio waves are investigated by using a three-dimensional ray-tracing computer program. Ray-path trajectories are presented for different values of the elevation angle of transmission. From our study, it was found that large-scale irregularity structures of the high-latitude ionosphere, in the presence of the earth's magnetic field, significantly affect high frequency radio wave propagation. 相似文献
5.
Summary This paper discusses a class of stochastic models of flow through porous media in which the randomness is attached to the structure of the medium rather than to the flow path. These models are obtained by generalizing an earlier model available in the literature where a regular crystal was taken in which bonds (flow channels) were dammed in a random fashion, yielding a random maze. The hydraulic properties of general models of this type are calculated; in particular, it is shown that they exhibit the phenomenon of dispersion whereby the factor of dispersion turns out to be a linear function of the percolation velocity. 相似文献
6.
A recently proposed general definition of wave breaking is further discussed, in order to deal with some points on which misunderstanding appears to have arisen. As with surface and internal gravity waves, the classification of Rossby waves into breaking and not breaking is a generic classification based on dynamical considerations, and not a statement about any unique signature or automatically recognizable shape. Nor is it a statement about passive tracers uncorrelated with potential vorticity on isentropic surfaces. A strong motivation for the definition is that proofs of the nonacceleration theorem of wave, mean-flow interaction theory rely, explicitly or implicitly, on a hypothesis that the waves do not break in the sense envisaged.The general definition refers to the qualitative behaviour of a certain set of material contours, namely those, and only those, which would undulate reversibly, with small slopes, under the influence of the waves' restoring mechanism, in those circumstances for which linearized, nondissipative wave theory is a self-consistent approximation to nonlinear reality. The waves' restoring mechanism depends upon the basic-state vertical potential density gradient in the case of gravity waves, and upon the basic-state isentropic gradient of potential vorticity in the case of Rossby waves. In the usual linearized theory of planetary scale Rossby waves on a zonal shear flow, the relevant material contours lie along latitude circles when undisturbed. 相似文献
7.
We consider a general stochastic branching process,which is relevant to earthquakes as well as to many other systems, and we study the distributions of the total number of offsprings (direct and indirect aftershocks in seismicity) and of the total number of generations before extinction. We apply our results to a branching model of triggered seismicity, the ETAS (epidemic-type aftershock sequence) model. The ETAS model assumes that each earthquake can trigger other earthquakes (aftershocks). An aftershock sequence results in this model from the cascade of aftershocks of each past earthquake. Due to the large fluctuations of the number of aftershocks triggered directly by any earthquake (fertility), there is a large variability of the total number of aftershocks from one sequence to another, for the same mainshock magnitude. We study the regime in which the distribution of fertilities is characterized by a power law ~1/1+. For earthquakes we expect such a power-distribution of fertilities with =b/ based on the Gutenberg-Richter magnitude distribution ~ 10–bm and on the increase ~ 10–m of the number of aftershocks with the mainshock magnitude m. We derive the asymptotic distributions pr(r) and pg(g) of the total number r of offsprings and of the total number g of generations until extinction following a mainshock. In the regime < 2 for which the distribution of fertilities has an infinite variance, we find
This should be compared with the distributions
obtained for standard branching processes with finite variance. These predictions are checked by numerical simulations. Our results apply directly to the ETAS model whose preferred values =0.8–1 and b=1 puts it in the regime where the distribution of fertilities has an infinite variance. More generally, our results apply to any stochastic branching process with a power-law distribution of offsprings per mother 相似文献
8.
Josef Kabeláč Reviewer D. Vítková Reviewer J. Vondrák 《Studia Geophysica et Geodaetica》1976,20(1):1-9
¶rt; u n ¶rt; (nmu) muauu m m naaamu auu
. am mu uu nu unauu ¶rt;a mu ¶rt; nuu u umuau. am ¶rt; ¶rt;u ¶rt;uua u nuam n uu. ¶rt;m uau u au nm u mnum ¶rt;a. a mm n¶rt;a ±0,1 naaamu auu
¶rt; um amu ¶rt; z=80° u ¶rt; m u ¶rt; =10 (uuaa). u¶rt;um nm u au am[2]. 相似文献
9.
Summary The components of the tidal torques along the axes of the inertia ellipsoid of a perfectly elastic Earth have been derived quite independently of the density distribution of masses within the Earth. It has been demonstrated that not only the sectorial, but also the tesseral terms in the tidal forming potential are responsible for the tidal deceleration of the Earth's rotation.
am ¶rt; mau ma nuu u m u a um unu¶rt;a uuu u¶rt;a n u, auu m ¶rt;a an¶rt;uu nmm a. aa, m nuu a¶rt;u au u a m muau, u mau nuuu au nuua nmua.相似文献
10.
Long-period recordings of dispersive Rayleigh waves along numerous station lines, or profiles, in Europe have for the first time permitted a uniform inversion of these observations based on a new method of phase velocity regionalization.Regional dispersion relations obtained by this method have then been subjected to a complete inversion procedure commonly known as the hedgehog method. The results are presented in a map outlining the thickness of the lower lithosphere (lid) and the shear (S) velocities in both the lid and the asthenosphere channel.A comparison of these results with the minimum compressional (P) wave velocities in the asthenosphere and their corresponding depths provides an estimate of theV
p
/V
s
ratio for the asthenosphere in the European area.Contribution No. 314, Institute of Geophysics, ETH-Zürich, Switzerland. 相似文献
11.
Summary We search for the effects of the interplanetary magnetic field (IMF) sector boundary crossing (SBC) in upper stratospheric ozone. The SBUV data (Nimbus-7) at the 10, 3 and 1 hPa levels are analysed for latitudes 45° N and 55° N for winters of the period December 1979 to December 1982. An effect of the IMF SBC wos only found at the 10 hPa level. These first results concerning the IMF SBC effect in upper stratospheric ozone are rather preliminary.
¶rt;m uu nu mau () nam aum n () a mam. SBUV ¶rt;a (u-7) a nm ¶rt;au 10, 3 u 1a aauum ¶rt; um 45° u 55° . . ua nu¶rt;a ¶rt;a 1979 – ¶rt;a 1982. m uu a¶rt; m a 10a. mu n mam n uuu a mam m n¶rt;aumu.相似文献
12.
Summary The interpretation of surface seismic waves records is rather complicated as they include a superposition of oscillations of the fundamental mode and higher modes. Besides recorded oscillations depend on spectral characteristics of motions in earthquakes sources. The consideration of these problems is based on results of surface waves two-dimensional modelling [1]3. Some physical ideas about their formation deals with the change of the nature of the oscillation propagating with dispersion. This report represents a condensate of several independent works. , , . , . , . () . .Scientific communication presented to the IASPEI Assembly, Madrid, 1969. 相似文献
13.
V. L. Gayevsky L. N. Guseva K. Ya. Kondratyev Ye. P. Novoseltsev N. Ye. Ter-Markaryantz V. F. Zhvalev 《Pure and Applied Geophysics》1968,69(1):336-359
Summary This paper considers a number of questions concerning the interpretation of infrared pictures of the earth taken from space. Long period mean statistical values of the contrasts in radiation temperature between the earth's surface and clouds for a number of points in the U.S.S.R. in different seasons have been calculated which makes it possible to conclude when and where clouds against the underlying surface can be detected as well as to formulate the requirements which the instruments mounted on a satellite are to satisfy. The blackness coefficients of clouds at different layers have been theoretically determined, the investigation of the problem of the spectral regions selection for satellite observations has been conducted. The worked out calculation scheme has been used in the solution of the problem of the possibility of satellite detection of such thermal non-homogeneities as sea currents and jet streams in the atmosphere. Examples of the synoptical analysis of the infrared pictures of the cloud cover obtained with the help of the NIMBUS-1 and COSMOS-122 satellites have been considered. , . , , , , . , . , , . , -1 -122. 相似文献
14.
Jana Konopásková Vlastislav Červený Reviewer I. Pšenčík 《Studia Geophysica et Geodaetica》1984,28(1):19-35
m¶rt;au n unm ¶rt; u ¶rt;uau uu n m nm ¶rt; ¶rt;. a uau ¶rt;m a ma m nau a¶rt;a, amu aa mu. au mu uu naam, m m¶rt;au n ¶rt;am ¶rt;mam m mam ¶rt;a u amu aa mu (. u. 9). aumu amu, uauau n ma nam ¶rt;a . ¶rt; amu m am ¶rt;m ¶rt;am mumm mam a naama am, an. aa uuau n, naama uauau n, um¶rt;. 相似文献
15.
Weakening of a prestressed sawcut in Westerly granite under laboratory condition is accomplished by injecting pressurized fluid into the sawcut. After injection a sequence of stick-slips is observed while the deviatoric stress decreases successively with each stick-slip. On the basis of the experimental observation we develop a model of fault instability due to inhomogeneous and progressive weakening of the fault. According to this model, the fault surface is divided into the slipped and the locked regions, depending on whether or not the local state of stress satisfies the friction criterion. The average shear stress in the slipped region decreases with time and, in order to maintain a quasi-static equilibrium, shear stress in the remaining locked region on the fault surface increases. This situation may last until a critical state of stress on the fault is met, at which a sudden instability (stick0slip) may occur. We suggest that this mechanism of stress transfer may be a viable mechanism of induced seismicity and aftershocks, in addition to the well-known mechanism of a local increase of pore pressure. By comparing the experimental data with model predictions we show that the critical condition for slip instability is when the average shear stress over the locked region becomes equal to the value given by the friction criterion. Thus the friction criterion established for slip on fractures on which the state of stress is macroscopically uniform may also be applicable to fractures on which the stress state is macroscopically heterogeneous. 相似文献
16.
Summary Determination of the gravitational effect of some bodies, the density of which is supposed to be variable in the vertical direction, possibly in the horizontal direction, too.
n¶rt;uaumau ma m m, nmm m um mua uu muma anau.相似文献
17.
Jan Pretel Lilian Kiršnerová Reviewer K. Vaníček 《Studia Geophysica et Geodaetica》1987,31(4):390-396
Summary To be able to parameterize vertical heat and water vapour fluxes in the boundary layer of the atmosphere, it is necessary to determined, among other factors, the amount of incident total radiation under a generally arbitrary condition of the atmosphere at any instant of time. This paper deals with a simple model for computing the total radiation based on known solar elevation, total cloud cover and the atmospheric turbidity parameter. This variant of the model was formulated on the basis of a two-year series of total radiation observations made in the radiation network of the Czech Hydrometeorological Institute, and on the measurements and observations made at the observatory of the Institute of the Physics of the Atmosphere in Kopisty. An example of comparing the observed and theoretical values of total radiation will also be given.
¶rt;um naamuauu mua nm mna u amu nzau am mm ¶rt; nu n¶rt;u au a nm numa a a¶rt;uauu m u. mam auam n naamuauu a a¶rt;uauu n ¶rt;a m a, ammu am u mnu az na. ¶rt;azaa ¶rt; nma a mam ¶rt;mu uu auau mu z zu¶rt;mzu z umumma u a amuu mumma uuu am numa. mam ma nu¶rt; nu au u u n n¶rt; ¶rt;u u au a a¶rt;uauu.相似文献
18.
The pirmary objective of this paper is to review inversion algorithms employed to interpret magnetotelluric data by the geophysical/electromagnetics group at Brown University. Examples are presented from a variety of tectonic regimes — the Rio Grande rift, the Colorado Plateau, and Iceland. Following a brief tutorial in which the basic relations for the inverse prrolem are developed, we discuss the detectability and resolvability of various elements of the models. The correlation between certain model parameters is stressed, a phenomena well-known to interpreters. In this paper we emphasize the importance of identifying the precise range of values for which two or more parameters are coupled — these ranges are defined by what wer term saturation limits. Generalized inverse theory is employed to arrive at optimal models which are evaluated in terms of resolution and information matrices. The degree to which models fit a given dat base can be assessed using several quantitative approaches. We have found that it is impotant not only to determine the best fitting model, but also to identify those marginal solutions which also fall within the range of uncertainty of the data. The results from our direct invverse method agree favorably with those from Monte Carlo methods. 相似文献
19.
u¶rt;um u ¶rt; n¶rt;u mum n -nuuu ¶rt;u um um ¶rt;¶rt; ¶rt; mm. um m u m u m¶rt;. 相似文献
20.
Karel Prikner Vladimír Vagner Reviewer M. Hvoždara 《Studia Geophysica et Geodaetica》1988,32(1):84-100
Summary The method of numerical modelling of ionospheric filtration of the Fourier components of a signal from the frequency range of Pc1 micropulsations is employed in the spectral analysis (frequency f, angle of incidence ) of the relative characteristic of the amplitude and energy reflectivity of the ionospheric layer with respect to ordinary Alfvén modes incident in the meridional plane. The results are presented for four different models characterizing the midlatitude day- and night-time ionosphere under low and high solar activity. The results indicate the specificity of filtration of ordinary Alfvén waves. It is proved that the lower region of the modelled ionosphere, as part of the midlatitude ionospheric wave guide (in particular the F2 layer), behaves like an Alfvén resonator in the given spectral range.
m¶rt; u ¶rt;uau u umauu -mau uaa u amm ¶rt;uanaa unau 1 n¶rtum nma aau (amma f, a¶rt;u ) mum anum¶rt; u mu maamu u ¶rt; ¶rt; a, a¶rt;au a u u¶rt;ua nmu. mam n¶rt;aam ¶rt; m a ¶rt; ¶rt;um m ¶rt; u u nu u u nu amumu. aam nuum umauu a. naa, m ua am ¶rt;ua u (a am F2-u ¶rt;um ¶rt;a) ¶rt;m nma ¶rt;uana a am a.相似文献