摘要:

A summary is given of present geophysical data available for the eastern Mediterranean, and the structural and tectonic history of the area is interpreted. The western Mediterranean is described in sufficient detail only for comparison.The region is delineated into plates on the basis of seismic activity at their margins. The African plate is moving northward relative to Europe with crustal destruction and underthrusting occurring along the Crete and Calabrian island arc systems. The intervening Aegean, Apulian, and Turkish plates are small and rapidly moving; they show intense seismicity at the boundaries. All observations (sediment deformation, gravity, magnetics and heat flow) suggest the existence of a zone of compression in the eastern Mediterranean.Anticlockwise rotation relative to Eurasia of parts of southern Europe occurred during an extensional phase in the west, permitting the development of new oceanic crust and accompanied by compression in the east. What little evidence there is suggests that the crust in the eastern Mediterranean is oceanic, but there are no magnetic stripes to indicate the orientation of the mid‐oceanic ridge from which it develope

ISSN:8755-1209    

DOI:10.1029/RG009i002p00189

年代:1971

数据来源: WILEY

摘要:

According to tidal friction calculations in which estimates of the current dissipation factor are used, the moon was close to the earth less than two billion years ago. The most plausible solution to this ‘time scale’ problem appears to be a much lesser extent of shallow seas in the past; a coupling of the moon's orbit with Venus is also a possibility. The same calculations indicate that the moon had an inclination of at least 10° to the equator, and that the earth's rotation period was five hours. Fission hypotheses, of which the most carefully developed is by O'Keefe, have not yet dealt successfully with these constraints. Fission theories are also unsatisfyingly episodic: matter must first lose angular momentum to fall into the earth, and then regain it to separate. All capture hypotheses are inherently improbable, particularly if the moon came from a different enough part of the solar system to account for the moon's density difference. The least implausible capture hypothesis, by Urey and MacDonald, entails collision with a pre‐existing earth satellite at 30–40 earth radii, but the reasoning behind it is not compelling. Most compatible with the idea that formation of the moon is closely connected to the formation of the earth are hypotheses that the moon formed out of a geocentric swarm of matter to which matter from heliocentric orbit was continually added. The theory of Ruskol seems to incorporate most of the dynamical essentials. However, the model needs to be developed further to include gas drag and other effects of the severe heating associated with chemical fractionation between the earth and moon, as well as to account for the inclination of the lunar orbit. A possibly severe constraint on the distance from the earth at which the moon's formation was completed is a systematic ellipticity of lunar craters pointed out by Öpik; it should be re‐examined after oriented metric photographs from Apollo 15–17 flights

ISSN:8755-1209    

DOI:10.1029/RG009i002p00217

年代:1971

数据来源: WILEY

摘要:

The available data on the terrestrial influx of small meteoric particles (mass<1 gram) are surveyed. Whereas, in the past, flux determinations differed by factors of as much as 100 million, it is shown that recent experimental data are far more consistent, variations being limited to a factor of 10 for particles of mass greater than 10−10gram. The sensors from which the data are obtained are discussed, with particular emphasis on those used in situ, and inherent uncertainties in the results are pointed out. A best estimate of the cumulative mass distribution influx is given on the basis of the most recent data available. This estimate uses the NASA Meteoroid Environment Model, 1969. Uncertainty limits due to differing experimental results and interpretations are placed upon this flux model. For masses larger than about 10−10gram, the uncertainty is less than 1 order of magnitude; whereas for smaller particles the uncertainty may still be as large as 4 or 5 orders of magnitude. The present best estimate of the mean density of the small meteoric particles is 0.5 g/cm³, but there are indications that several classes of meteoroids exist with densities ranging from 0.3 to 1.2 g

ISSN:8755-1209    

DOI:10.1029/RG009i002p00239

年代:1971

数据来源: WILEY

摘要:

The use of satellite scalar magnetic field data to produce geomagnetic field models is reviewed. There have been nine separate spacecraft that have acquired observations of the geomagnetic field from low (<1500 km) satellite altitudes since 1958. The magnetic field models produced from such data have not been sufficiently compared with surface vector data to firmly, establish their validity. One comparison has indicated that satellite‐derived models are as valid over‐all as those produced from surface data. Variations in the field components are shown to be larger than those in scalar field by factors of 4–10. Recent satellite models indicate an increase in dipole decay to −27 γ/year, a value that may be plausible, judging from extrapolation of earlier surface‐derived models. Also noted is a recent slowing of eccentric dipole west

ISSN:8755-1209    

DOI:10.1029/RG009i002p00259

年代:1971

数据来源: WILEY

摘要:

A comprehensive review is made of the observational history of the gegenschein with emphasis on its physical parameters: size, shape, brightness, spectrum, position, and parallax. The theories that have been considered tenable until recently are critically discussed. The libration point, gas tail, and dust tail hypotheses can be disproved, whereas the heliocentric dust cloud hypothesis is consistent with all evidence available. At present the asteroid belt seems to be the most likely source of the material producing the gegenschein. A short discussion of the false zodiacal light is included.

ISSN:8755-1209    

DOI:10.1029/RG009i002p00275

年代:1971

数据来源: WILEY

摘要:

This paper is devoted to a critical review of photoabsorption cross sections for molecules of aeronomic and astrophysical interest at wavelengths less than 3000 A. A discussion of the relative merits of various experimental techniques is given along with possible systematic and random errors that may be associated with them. The problems in data analysis associated with finite spectral bandwidths are reviewed, with special emphasis on the interpretation of published absorption cross sections. This review does not contain a complete set of cross‐section‐versus‐wavelength values for each molecule; the prepared figures are used to compare the results of several determinations or to point out where difficulties of interpretation might arise. However, references to all papers believed to contain the more reliable data are

ISSN:8755-1209    

DOI:10.1029/RG009i002p00305

年代:1971

数据来源: WILEY

摘要:

This paper reviews experiments under way or contemplated that make use of space vehicles for the quantitative study of gravitation. Several experiments are discussed briefly, some which can be performed in earth orbit, and others which require deep space probes. It is anticipated that the decade of the 1970's will place the relativistic theory of gravitation on a firm experimental basis.

ISSN:8755-1209    

DOI:10.1029/RG009i002p00407

年代:1971

数据来源: WILEY

摘要:

The analyses that have led to the finding of a new polar magnetic disturbance are reviewed, and a unified picture is presented. Although the new disturbance has been reported under various names, an essential common feature is that the disturbance does not originate from the auroral electrojet. The high correlation observed between the disturbance and the orientation of the interplanetary magnetic field suggests that the disturbance reflects a basic interaction process between the solar wind and the magnetosphere.

ISSN:8755-1209    

DOI:10.1029/RG009i002p00417

年代:1971

数据来源: WILEY

摘要:

Several quite dissimilar models have been proposed for the direct interaction of the solar wind with planetary ionospheres, based, respectively, on the assumption of (1) restricted flow into the ionosphere, (2) an interface between the solar wind and the ionospheric plasma, or (3) a magnetic field barrier (‘induced magnetopause’). All three require the existence of a standing bow shock in the solar wind. We review these models, discuss their individual limitations, and consider what observational data would distinguish among t

ISSN:8755-1209    

DOI:10.1029/RG009i002p00427

年代:1971

数据来源: WILEY

摘要:

Observations from space vehicles have vastly altered our conceptions of Mars and Venus. Mars has changed from an earth‐like planet with water ice caps into a heavily cratered, coreless object whose polar caps are dry ice and whose tenuous atmosphere is CO2. Venus has been found to be blanketed by clouds and a dense CO2atmosphere that has driven the surface temperature to 700–800°K. Attention is drawn to the practical returns we can expect from comparative studies of these three planets: for understanding of the origins of life, the potential development of a runaway greenhouse effect on earth, and atmospheric circula

ISSN:8755-1209    

DOI:10.1029/RG009i002p00437

年代:1971

数据来源: WILEY