摘要:

We report laboratory results on sound velocities of granite, either sheared to rupture or undergoing stick‐slip sliding. We found that the variations in velocity premonitory to these two types of instability are dramatically different. Velocities of both compressional and shear waves decreased significantly prior to the occurrence of rupture, while no change was found during the stick‐slip motion. We suggest that for shallow earthquakes appreciable variation in the faulting processes is likely: Some faulting may be associated with pervasive dilation and fracturing of surrounding rocks, while others may involve little such processes. These variations may be the cause for the conflicting findings in the variations of seismic velocities premonitory to earthqua

ISSN:0094-8276    

DOI:10.1029/GL002i008p00309

年代:1975

数据来源: WILEY

摘要:

An analysis of records of multiply reflected ScS phases from ten deep‐focus earthquakes yields near‐vertical one‐way travel‐time residuals varying from +5.0 to −3.5 s. Continental and oceanic residuals overlap and both indicate large lateral variations. Similar values are found for the older oceanic basins and for continental shields. Most, if not all, of the variations can be attributed to differences in the lithosphere and asthenosphere. The mantle under Hawaii, Iceland and Trindade (South Atlantic) Islands is anomalously slow, all being postulated hotspots. In the case of Trindade, petrological data is consistent with a pronounced low‐velocity zone and large S delays. Some recent studies assumed that stations on oceanic islands were representative of the ocean as a whole and it has been suggested that continent‐ocean differences extend deeper than 400 km. The present results indicate that oceanic islands are anomalous, and that differences between oceans and continents need not extend below 200 km. This does not rule out the existence of deep lateral inhomogeneities, but only the proposal that continents, in general, are faster than oceans to depths greate

ISSN:0094-8276    

DOI:10.1029/GL002i008p00313

年代:1975

数据来源: WILEY

摘要:

The explicit volume dependence of the vibrational part of the free energy is derived in terms of the first two moments of the mode gamma distribution and general characteristics of the lattice potential. Contrary to what is generally assumed, the approximation 〈γ²〉 = 〈γ〉² is inadequate for compounds in the NaCl structure and the distribution in mode gamma values has a significant contribution to the volume dependence of the Grüneis

ISSN:0094-8276    

DOI:10.1029/GL002i008p00317

年代:1975

数据来源: WILEY

摘要:

The synthesis of extensive seafloor heat‐flow and subsidence data for the North Atlantic and North Pacific Oceans reveals that these quantities approach equilibrium values before the oceanic lithosphere is 80 million years old. These are fundamental constraints on any model describing the thermal evolution of the oceanic lithosphere, but previously they have not been well established and have been ignored in recent thermal models. To satisfy these constraints, either the lithosphere must establish a nearly constant thickness by interacting with the asthenosphere, or a tenuous set of conditions interrelating plate thickness, density changes, basal heat flow, and asthenosphere temperature gradients must prevail. Failure to recognize this has led to the acceptance of thermal models that are inconsistent with a vast amount of oceanographic dat

ISSN:0094-8276    

DOI:10.1029/GL002i008p00321

年代:1975

数据来源: WILEY

摘要:

Direct field measurements of the washout of submicron aerosols by snow have been accomplished by high‐speed sampling of the atmospheric aerosol spectrum and of the rate of snowfall. For the aerosol size range 0.29 µm ≤ D ≤ 1.48 µm, the values of the measured washout coefficients are 4.82×10−4≤ λS≤ 6.35×10−3sec−1, and show no systematic dependence on aerosol diameter. Comparison of the results with those previously derived for rain washout indicate that snow scavenging is ∼28–50 times more efficient per equivalent water content. Average aerosol lifetimes due to washout by snowfall are of the order of 0.7 hours, thus establishing snow scavenging as the dominant aerosol sink in regions having significant snowfall

ISSN:0094-8276    

DOI:10.1029/GL002i008p00325

年代:1975

数据来源: WILEY

摘要:

Concentrations of particles having radii<0.1 µm (Aitken particles) in the stratosphere immediately above the tropopause were measured with a condensation nucleus counter during horizontal flights of a jet aircraft. Order‐of‐magnitude variations in the concentrations were observed which may have resulted from the interaction of gravity waves with strata of the particles. Since the concentrations of Aitken particles are usually an order of magnitude or more smaller than those of ions in the stratosphere, it is likely that at most only a small fraction of such ions play an important role in the production of stratospheric parti

ISSN:0094-8276    

DOI:10.1029/GL002i008p00329

年代:1975

数据来源: WILEY

摘要:

The thermodynamic properties of several water‐soluble gases are reviewed to determine the likely effect of the atmospheric water cycle on their vertical profiles. We find that gaseous HCl, HNO3, and HBr are sufficiently soluble in water to suggest that their vertical profiles in the troposphere have a similar shape to that of water vapor. Thus we predict that HCl, HNO3, and HBr exhibit a steep negative gradient with altitude roughly equal to the altitude gradient of water vapor. Therefore, ground‐based sources of inorganic chlorine, odd nitrogen, and inorganic bromine compounds are not likely to directly affect the stratosphere in the mean. Calculations also show that while SO2and NH3are significantly affected by the atmospheric water cycle, their abundances may not decrease with altitude as rapidly as does water va

ISSN:0094-8276    

DOI:10.1029/GL002i008p00333

年代:1975

数据来源: WILEY

摘要:

The open source neutral mass spectrometer (OSS) on the Atmosphere Explorer‐C satellite (AE‐C) measures the neutral constituents of the upper atmosphere. It has been found that atomic nitrogen densities can be determined at altitudes above 380 km. Most of the nitrogen atoms combine with oxygen adsorbed on the walls of the ion source to form NO. The measured net peaks at 14 amu and 30 amu show the scale height expected for atomic nitrogen; both peaks have a pronounced diurnal variation. We computed absolute number densities at 400 km for a time period between February and April 1974 when measurements were taken in the northern hemisphere. Minimum and maximum densities of atomic nitrogen occur between 4 and 6 hr LST in the morning and around 16 hr LST in the afternoon, respectively. At 400 km the minimum particle density is 1.0 × 105cm−3and the maximum density 1.5 × 106cm−3. In contrast to the response of N2to geomagnetic activity, atomic N shows no appreciab

ISSN:0094-8276    

DOI:10.1029/GL002i008p00337

年代:1975

数据来源: WILEY

摘要:

Theoretical models have been used to investigate the effects of artificially injected H2gas on plasma densities in the ionospheric F region and the overlying protonosphere. Owing to large reaction rates between H2and ionospheric O+ions, plasma densities in both daytime and nighttime ionospheres can be greatly reduced by modest amounts of H2gas released. 100 kg of H2released at 300 km altitude reduces local O+densities by more than three orders of magnitude and produces ∼5% depression in H+densities in the overlying protonosphere. These results suggest that it should be possible to conduct controlled chemical modification experiments for investigation of many outstanding ionospheric and magnetospheric problem

ISSN:0094-8276    

DOI:10.1029/GL002i008p00341

年代:1975

数据来源: WILEY

摘要:

First results of comprehensive observations of magnetic and electric fields, and ambient and suprathermal plasmas above the dayside auroral oval with rocket‐borne instrumentation which penetrated the cleft region are reported. Measurements were also obtained equatorward and poleward of the cleft. Convection velocities as inferred from electric field measurements were generally toward noon equatorward of the cleft and were antisunward over the polar cap. Our observations of electron temperatures, electric fields and low‐frequency electrostatic noise provide strong evidence of a plasma instability (Farley‐Buneman) in the E‐layer, which is associated with the appearance of the ‘slant E condition’ identified in ground‐acquired ionograms. The positions of these measurements relative to that of the cleft were firmly established via the determination of the plasma environment with an electrost

ISSN:0094-8276    

DOI:10.1029/GL002i008p00345

年代:1975

数据来源: WILEY