摘要:

The adsorption of vapor on the internal surface of a sandstone reduces its frame moduli. A theoretical model has been developed which predicts the weakening as a function of fluid chemistry and effective pressure. The model is based on well established contact theory and surface chemistry. Frame moduli are directly proportional to the stiffness of the grain contacts. The contact stiffness is dependent on surface energy. We show how the adsorption of various chemicals onto quartz surfaces lowers the surface energy, thereby weakening the contact stiffness. The predicted variation of frame moduli with the partial pressure and chemical species is qualitatively consistent with recent experimental results. The calculations suggest that the chemical effect is only significant at low effective pressures. At high pressures, the elastic loading dominates the contribution due to surface energy.

ISSN:0094-8276    

DOI:10.1029/GL011i009p00805

年代:1984

数据来源: WILEY

摘要:

Long‐range recording of COCORP vibrators was undertaken in the Adirondacks using a radio repeater to retransmit the vibrator start‐up code at ranges up to 100 km. A number of events were recorded at a range of 47 km; these events correspond to reflections from depths of about 9, 13, 16, 20, and 24 km and a possible Moho reflection from 40 km might be present. Simulation of VIBROSEIS recording demonstrates that low‐level signals with a S/N as low as 0.05 may be extracted from noise even though reflections have amplitudes less than the least significant bit. Such wide‐angle VIBROSEIS recording is practical and necessary in crustal reflection studies for defining the Moho and other deep ref

ISSN:0094-8276    

DOI:10.1029/GL011i009p00809

年代:1984

数据来源: WILEY

摘要:

Macdonald Volcano, located at the younger end of the Austral Islands chain and discovered in 1967 from teleseismicTwaves, has been the site of intense volcanoseismic swarms from 1977 to January, 1984. Three new surveys of its summit, including by scuba divers, have revealed pinnacles reaching 27 m b.s.l., and a variety of fresh features, such as fractures and spatter cones. It is strongly suggested that the summit of the volcano swelled and the pinnacles grew since Johnson’s last survey in 197

ISSN:0094-8276    

DOI:10.1029/GL011i009p00813

年代:1984

数据来源: WILEY

摘要:

Recent conflicting results on the mechanism of the olivine‐spinel phase transition suggest that the mechanism varies with experimental conditions. Evidence for a shear‐induced mechanism is strong in experiments performed at temperatures far from the melting point or under conditions where very large shear stresses may be inferred. Where temperatures are closer to the melting point and stress concentrations probably less severe, the evidence favors a nucleation and growth mechanism. In one study, volume reduction accompanied anion restacking and significantly preceded cation reordering, suggesting a change in bonding between the two polymor

ISSN:0094-8276    

DOI:10.1029/GL011i009p00817

年代:1984

数据来源: WILEY

摘要:

Ellipsoidal height differences have been determined for 13 station pairs in the central Ohio region using measurements made with the Global Positioning System. This information was used to compute geoid undulation differences based on known orthometric heights. These differences were compared to gravimetrically computed undulations (using a Stokes integration procedure and least squares collocation having an internal r.m.s. agreement of ±1 cm in undulation differences). The two sets of undulation differences have an r.m.s. discrepancy of ±5 cm while the average station separation is of the order of 14 km. This good agreement suggests that gravimetric data can be used to compute accurate geoid undulation differences that can be used to convert ellipsoidal height differences obtained from GPS to orthometric height difference

ISSN:0094-8276    

DOI:10.1029/GL011i009p00821

年代:1984

数据来源: WILEY

摘要:

Estimation of confidence limits on net tectonic rotation by an ‘overlapping circles’ method can lead to values which are too large. A simple method based upon an F‐ratio test is presented which yields more accurate constraints on net rotation. An example illustrates that the limits calculated by the ‘overlapping circles’ method can be in error by more

ISSN:0094-8276    

DOI:10.1029/GL011i009p00825

年代:1984

数据来源: WILEY

摘要:

Layered and massive gabbros of the Humboldt Lopolith and extrusive equivalents in west‐central Nevada yield well‐grouped paleomagnetic data on a site basis. With corrections for attitudes of compositional layering in gabbros and flow contacts in lavas (kcorr/kin situ= 5.5), the mean of 15 site means is: D = 307°, I = 21°, α95= 9°, k = 17. While K‐Ar data imply a Late Jurassic age, we prefer an older, probably Early Jurassic, age for the lopolith and its magnetization based upon magnetization data and relations of these rocks with host strata. Compared with Early Jurassic expected directions, the data reveal a discordancy in declination of −37° (+/− 14‐22°) which implies a significant counterclockwise rotation of the lopolith. Local rotation of Fence‐maker allochthon units most likely occurred when southeasterly‐directed thrust sheets obliquely contacted a generally north‐south trending shelf margin. Mesozoic deformation will be more accurately estimated with better age control and measurement of possible Ce

ISSN:0094-8276    

DOI:10.1029/GL011i009p00828

年代:1984

数据来源: WILEY

摘要:

The variation of low‐field magnetic susceptibility with low temperature (between ˜77°K and ˜300°K) observed for a vertical columnar basalt from central Mexico shows a rare pattern for continental basalt ‐ i.e. susceptibility decreases with temperature to about 40‐70% of room‐temperature value, and then increases up to about 60‐100% at 77°K. These results combined with other rock‐magnetic measurements, including AF and thermal demagnetization, IRM experiments, Lowrie‐Fuller tests, thermomagnetic analysis, and optical and SEM observations suggest the presence in the columnar basalt of predominantly single domain and pseudo‐single domain titanomagnetites with composition around TM60, and a small amount of very fi

ISSN:0094-8276    

DOI:10.1029/GL011i009p00832

年代:1984

数据来源: WILEY

摘要:

Samples from glacial varves were obtained by cutting cubes and by pushing plastic cubical containers into the sediment. The anisotropy of magnetic susceptibility results show that the mean angular difference in the kmaxdirection can be altered by 32° by pushing in the sample containers in a north to south versus an east to west direction. The values of lineation and Q are raised or lowered dependent upon the direction of push and the original fabric direction.Mean remanence directions can deviate by as much as 43° in a single clay layer dependent upon the direction in which the sample containers are inserted into the sediment. Corresponding changes in mean intensity of the remanence also demonstrate that the remanence has been affected by pushing in sample containers. The overall results underline the need to adopt trustworthy procedures for the sampling of soft sediments deposited by settling and tractio

ISSN:0094-8276    

DOI:10.1029/GL011i009p00836

年代:1984

数据来源: WILEY

摘要:

The angular momentum budget of the atmosphere requires that there be an upward transport of angular momentum in the tropics and a downward transport at midlatitudes. The vertical transport in the tropics is thought to take place in the cores of deep convective clouds, and the same convective activity is thought to play a dominant role in determining the height of the tropopause in the tropics. Accordingly, the average height of the tropical tropopause ought to be positively correlated with the angular momentum of the atmosphere relative to the earth’s surface. The existence of such a correlation on both annual and interannual time scales is show

ISSN:0094-8276    

DOI:10.1029/GL011i009p00840

年代:1984

数据来源: WILEY