摘要:

The prominent rille Rima Goclenius II, which crosses the lunar crater Goclenius nearly centrally, appears to have been formed as a secondary effect after the opening of a deep‐seated fracture. The main fracture was formed with an opening of about 175 meters along much of its length. A secondary dip‐slip fracture then appeared, and a wedge‐shaped piece of ground slid downward along this secondary fault, joining the primary fracture about 1 km below the present mare filling of Goclenius. The width of the resulting rille is a linear function of the absolute elevation of the ground along each point of the

ISSN:0148-0227    

DOI:10.1029/JB076i035p08459

年代:1971

数据来源: WILEY

摘要:

Calculations that will enable an experimenter to estimate the volume of material viewed by an air‐borne gamma‐ray spectrometer are presented. The effects of altitude, air density, source density, and gamma‐ray attenuation coefficient were investigated. It is shown that the altitude is the most important parameter in the determination of the volume of material that produces a given percentage of the total observed s

ISSN:0148-0227    

DOI:10.1029/JB076i035p08466

年代:1971

数据来源: WILEY

摘要:

Ten weeks of Doppler tracking of the 5 satellites for which data are available at the National Space Science Data Center have been analyzed to determine the coordinates of 27 tracking stations and the gravity field of the earth represented by the potential of a simple layer. Density values of this layer for 104 surface elements have been computed in a least‐squares adjustment and transformed into harmonic coefficients up to the eleventh degree and order. Comparisons with other solutions show good agreement. The results for the equatorial radius of the earth, its flattening, and its gravity at the equator are 6,378,156 meters, 1/298.255, and 978,028.8 mgal, respectivel

ISSN:0148-0227    

DOI:10.1029/JB076i035p08471

年代:1971

数据来源: WILEY

摘要:

Statistical tests with unit vectors have been very useful in paleomagnetism. R. J. Beran and G. S. Watson devised a test for serial correlation of unit vectors. This paper gives formulas that make this test computationally easy to apply. A test statistic based on the sum of the cosines of the angles between each pair of vectors is provided to test pairwise correlation of unit vectors. Computable formulas are given for the mean and variance in the randomization distribution of the test statistic. A Monte Carlo experiment is quoted in support of a normal approximation for its distribution.

ISSN:0148-0227    

DOI:10.1029/JB076i035p08480

年代:1971

数据来源: WILEY

摘要:

Whole‐rock Rb‐Sr data have been measured for 15 hypersthene chondrites including 10 black chondrites. The latter appear to have been the most heavily shocked and reheated. Several density fractions for two of the black chondrites, Orvinio and Farmington, were separated, and Rb‐Sr analyses were performed. Whole‐rock data for observed black hypersthene falls conform (within experimental error) to the 4.5–4.6×109‐year isochron defined by other chondrites. Although black ‘finds’ plot uniformly to the left of the isochron, this behavior is also shown by unshocked finds. Therefore the total‐rock data do not reveal any significant shock or reheating effects. The density separates, particularly those of Orvinio, depart significantly from the 4.5‐b.y. isochron. Although their87Rb/86Sr ratios vary from 0.5 to 1.1, their87Sr/86Sr ratios are the same as that of the total meteorite to within 0.002. This similarity results in a nearly horizontal distribution of points on a Sr evolution diagram. To a lesser extent, data from Farmington also show the same effect. It is concluded that this behavior is due to partial homogenization of the Sr isotopes within these two meteorites very recently in their history. The scatter in the data precludes any precise determination of t

ISSN:0148-0227    

DOI:10.1029/JB076i035p08484

年代:1971

数据来源: WILEY

摘要:

Large variations of the predominant frequencies and amplitudes of the seismic phasesPnandSnoccur for hundreds of paths that cross much of the region between the Tonga island arc and the Fiji islands. The data clearly delineate a region of high attenuation in the uppermost mantle behind the Tonga arc. The region of high attenuation, a zone about 300 km wide, is between the Tonga ridge (the frontal arc) and the Lau ridge (the third arc). The alignment of active volcanoes on the Tonga ridge seems to mark the eastern boundary of this high‐attenuation zone. If low attenuation, or highQ, correlates with strength, our observations indicate that the uppermost mantle is considerably weaker beneath the Lau basin, and a gap in or a substantial thinning of the lithosphere exists between the frontal arc and the third arc. This is in excellent agreement with the hypothesis that the Lau basin is the product of crustal extension. A detailed study of the variations of predominant frequencies ofPandSwaves that traverse the wedge of mantle above the inclined seismic zone of intermediate and deep earthquakes of Tonga shows that material with anomalously high attenuation is present throughout the prism of mantle above depths of about 150 to 300 km along the inclined seismic zone. That is, the data imply an anomalous increase in attenuation in the asthenosphere near the inclined seismic zone;Qmay be as small as 50 forPwaves and less than 20 forSwaves. Regions of anomalously high attenuation also exist behind several other island arcs in a position similar to that behind the Tonga arc. These zones seem compatible with models in which the asthenosphere material is mobilized by the descending lithospheric sla

ISSN:0148-0227    

DOI:10.1029/JB076i035p08493

年代:1971

数据来源: WILEY

摘要:

Several geophysical and tectonic features of the Aegean Island arc are described. An attempt has been made to interpret these features by means of a model of the area that includes a lithospheric plate that underthrusts the arc and moves from the Mediterranean to Europe. The upper boundary of this plate is determined by a zone of intermediate earthquakes. These earthquakes are located close to a surface of amphitheatrical shape that is dipping under the arc at a mean angle of about 30°. There is an aseismic zone in the upper mantle under the inner part of the arc. The absorption of short‐period body waves in this zone explains the observed abnormal distribution of the seismic energy in the area. The results of this work are in general agreement with the ‘new global tecton

ISSN:0148-0227    

DOI:10.1029/JB076i035p08517

年代:1971

数据来源: WILEY

摘要:

Geodetic networks with dimensions on the order of 40 meters to 2 km were established across the Denali, Fairweather, and Castle Mountain faults to measure slip by repeated annual triangulation. Within the resolution of the data, slip was not observed on any of the faults; specifically, horizontal and vertical slip, if not zero, was less than 3 mm on the Denali and Fairweather faults for 1967–1969 and 1968–1969, respectively, and less than 5 mm on the Castle Mountain fault for 1966–1969. The Denali and Fairweather faults are locally locked. In view of the high microearthquake activity and the available seismic and tectonic history, strain is likely to be accumulating at both sides. A conclusion about the strain accumulation on the Castle Mountain fault awaits additional seismic and tectonic data.A complete set of data, including networkdescriptions, observed and adjusted horizontaldirections, observed altitudes corrected forinstrument heights, and lengths of lines from adjustedangles, can be ordered from the AmericanGeophysical Union, Suite 435, 2100 PennsylvaniaAvenue, N.W., Washington, D.O. 20037. DocumentJ7‐002; $1.00 per microfic

ISSN:0148-0227    

DOI:10.1029/JB076i035p08534

年代:1971

数据来源: WILEY

摘要:

In this paper we set up the fundamental equations for the problem of a uniformly moving, two‐dimensional, liquid‐filled crack. It is shown that a solution exists for a crack moving with a velocity close to the Rayleigh‐wave velocity. However, in any practical situation a liquid‐filled crack can never gain enough kinetic energy to move so quickly. Another solution exists for a crack moving with such a small uniform velocity that for all practical purposes it is a stationary crack. It is concluded that a liquid‐filled crack in the earth's mantle or in a glacier will move with a non‐uniform motion at velocities considerably smaller than the Rayleigh‐

ISSN:0148-0227    

DOI:10.1029/JB076i035p08544

年代:1971

数据来源: WILEY

摘要:

Apparent‐velocity variations across the large‐aperture seismic array (Lasa) have been studied by usingPwaves from six teleseisms at different distances and azimuths around Lasa. Data from 13 instruments per subarray were used in the analysis. Average apparent velocities between subarrays, taken in pairs, were measured by using arrival‐time data. Apparent velocities at subarrays were estimated by a cross‐spectral method involving the whole signal shape. For the 2 events in the southeast direction, there is a large zone of low apparent velocity to the northwest of A0 subarray. For the events in the other azimuths, regions of low and high apparent velocities are clearly contourable across Lasa. It appears that a 30% variation in apparent velocity exists across Lasa for events from all azimuths. The apparent‐velocity measurements at subarrays, in general, follow the pattern shown by the measurements based on arrival‐time data. However, there are some significant differences, especially at the subarrays inEandFrings. The apparent‐velocity measurements indicate that structural complexities over and above those seen in the average crustal models proposed so far exi

ISSN:0148-0227    

DOI:10.1029/JB076i035p08554

年代:1971

数据来源: WILEY