摘要:

The interpretation of free air gravity anomalies over present day centers of postglacial rebound has always been controversial. We show that the observed gravity anomalies over both Fennoscandia and Laurentiaandthe associated relative sea level variations since deglaciation are explicable with a simple Newtonian viscoelastic model of the earth if the earth model includes the density jumps in the mantle associated with the phase transitions at 420 and 670 km depth. The result has important implications for mantle convection since the observed free air anomalies are very sensitive to the viscosity of the mantle beneath the deepest phase transition.

ISSN:0094-8276    

DOI:10.1029/GL009i007p00731

年代:1982

数据来源: WILEY

摘要:

The physical processes of the fusion of small cracks into larger ones are nonlinear in character. A study of the nonlinear properties of fusion may lead to an understanding of the instabilities that give rise to clustering of large earthquakes. We have investigated the properties of simple versions of fusion processes to see if instabilities culminating in repetitive massive earthquakes are possible. We have taken into account such diverse phenomena as the production of aftershocks, the rapid extension of large cracks to overwhelm and absorb smaller cracks, the influence of anelastic creep‐induced time delays, healing, the genesis of "juvenile" cracks due to plate motions, and others. A preliminary conclusion is that the time delays introduced by anelastic creep may be responsible for producing catastrophic instabilities characteristic of large earthquakes as well as aftershock sequences. However, it seems that nonlocal influences, i.e. the spatial diffusion of cracks, may play a dominant role in producing episodes of seismicity and clusterin

ISSN:0094-8276    

DOI:10.1029/GL009i007p00735

年代:1982

数据来源: WILEY

摘要:

Topography and gravity information for this 370‐km crater are analyzed to determine a depth of compensation using an Airy isostatic model. A least squares fit to the gravity profile produces an estimate of 115 km for the depth of compensatio

ISSN:0094-8276    

DOI:10.1029/GL009i007p00739

年代:1982

数据来源: WILEY

摘要:

Different techniques for measuring crustal deformation are now being tested at Piñon Flat Geophysical Observatory in southern California. As a part of this comparison, we have analyzed five months of data from four different tiltmeters: three borehole instruments, two 4.5 m and one 26 m deep; and a long‐base (535 m) instrument at the surface. For periods from 1 hour to 10 days, the signals from the deep borehole and long‐base instruments show comparable noise levels; the shallow instruments are much noisier. Tidal analyses give results for the different sensors which agree to within the errors, which are several per

ISSN:0094-8276    

DOI:10.1029/GL009i007p00743

年代:1982

数据来源: WILEY

摘要:

The data recorded by a synthetic aperture radar (SAR) can in principle be analyzed to obtain the radial velocity of moving objects in the scene relative to the flight path of the SAR platform. The application of this concept for measuring ocean surface currents has been evaluated using data from SAR systems mounted in aircraft and spacecraft platforms. This paper summarizes the results of these experiments and describes the system effects which can influence the measurement accuracy. Considerations involved in the design of optimum systems for this application are also discussed.

ISSN:0094-8276    

DOI:10.1029/GL009i007p00747

年代:1982

数据来源: WILEY

摘要:

Preliminary interpretation of pH and sodium concentration data for marine rains collected during February and July, 1981 at American Samoa (14°15′S, 170°34′W) as part of the Sea/Air Exchange (SEAREX) Program indicate that rain is usually slightly more acidic than would be expected on the basis of atmospheric CO2‐pure water equilibrium, in this remote region of the tropical South Pacific Ocean. The data are consistent with calculations of pH using the alkalinity equation for "model" solutions containing only sea‐salt and traces of strong acids in equilibrium with atmospheric CO2. Alkalinity due to sea‐salt appears to affect pH significantly only when the salinity of the rain is greater than 0.01 ‰ or 3000 µg Na/kg. The observed range of pH values is much smaller than has been observed recently at subtropical marine sites: this, along with the relatively high average pH value, suggests that climatic factors influence levels of acidity in rain over remo

ISSN:0094-8276    

DOI:10.1029/GL009i007p00751

年代:1982

数据来源: WILEY

摘要:

During the years 1974‐1979 the CCl3F concentration in the Northern Hemisphere stratosphere increased by a factor of 2. The annual rates of increase were directly related to annual rates of emissions at the surface of the earth. The production data for fluorocarbons, published by the Chemical Manufacturers Association, show a decline in the yearly rate of emission of CCl3F during the last decade. The yearly percent increase in the mean stratospheric concentration in the Northern Hemisphere has shown a similar decline. Data for CCl4, CCl2F2and SF6also show a slowing in the annual rate of increase in the stratospheric mean concentration. The calculated globally averaged concentration of N2O in the Northern Hemisphere remained constant at 249±7 n1/1 during the years 1976‐

ISSN:0094-8276    

DOI:10.1029/GL009i007p00755

年代:1982

数据来源: WILEY

ISSN:0094-8276    

DOI:10.1029/GL009i007p00759

年代:1982

数据来源: WILEY

摘要:

The fluxes of carbon, nitrogen and sulfur emitted to the atmosphere during bushfires in intertropical savannah zones are evaluated by measuring these three elements in various samples of plants and ashes collected before and after the fires in a savannah of Ivory Coast. We show that almost all the carbon and nitrogen, and over half the sulfur contained in the vegetation are released into the atmosphere during bushfires. Owing to the great extent of the areas burnt annually, this phenomenon constitutes an important spurge of C, N and S for the atmosphere : 1‐3.1×109ton carbon, 5‐15×106ton nitrogen and 0.4‐1.2×106to

ISSN:0094-8276    

DOI:10.1029/GL009i007p00761

年代:1982

数据来源: WILEY

摘要:

We show that the magnetohydrodynamic conditions of the Venus ionosphere near the terminator favor convection of magnetic field rather than diffusion. Consequently, any planetary magnetic field which Venus may possess will be strongly affected by the global antisunward flow of the ionosphere which has been revealed by the Pioneer‐Venus retarding potential analyzer. The magnetic flux from an internal magnetic field will accumulate in the night hemisphere. Details of the structure and dynamics of such accumulations depend on particular details of the magnetic field source and the time‐dependent plasma flow pattern, but a simple interpretation of observational data yields a magnetic dipole moment of 7 × 1020G cm³ directed along the planet spin v

ISSN:0094-8276    

DOI:10.1029/GL009i007p00765

年代:1982

数据来源: WILEY