Gravity and crustal movements: The canadian experience     

J.G. Tanner  A. Lambert 《Journal of Geodynamics》1987,7(3-4)

Repeated high precision gravity measurement have already played an important role in the detection of crustal deformation in Canada and elsewhere, but even more useful results can be expected through more widespread use of gravity in combination with other techniques. The crucial element in the process is the development of a good physical model on which the experiment can be based. Otherwise, considerable time and effort can be spent on determining the most appropriate field strategy.New technical developments on the horizon appear to offer enhanced opportunities for gravity studies of crustal processes. The coming availability of the Global Positioning System and transportable absolute gravimeters will open up the possibility of regional studies (i.e., areas of the order of 100 km or perhaps greater) of crustal movements at reasonable cost.Within Africa the development of an African Gravity Standardization Net will be a major first step in any program to provide a better understanding of the neo-tectonic framework of this vast continent.  相似文献   

REPEATED SHOCK AND THERMAL METAMORPHISM OF THE ABERNATHY METEORITE     

P. Lambert  C. Lewis  C.B. Moore 《Meteoritics & planetary science》1984,19(1):29-48

Based on the example of Abernathy (L6 chondrite), this study shows how petrographic investigation can be used to unravel the nature, chronology and conditions of superposed metamorphic events in chondrites. Features considered include the texture of the rock, optical characteristics of olivine, pyroxene and plagioclase, refractive index of plagioclase, metallographical characteristics and microhardness of Fe-Ni alloys. From these data it is deduced that Abernathy has been involved in at least six metamorphic events since the formation of the chondrite. Four distinct shock events and two separate reheating events have been identified. The chronology of these events is established. The conditions for the last four events are reasonably well constrained. These include successively, i) severe reheating (T > 1200°C), ii) severe shock causing complete melting of plagioclase and local melting of the rock (90 < P < 110 GPa, 1250°GC < T < 1350°C), iii) mild shock (10 < P < 25 GPa, T<500°C), and iv) reheating below 800°C.  相似文献   

The excitation of the forbidden coronal lines     

R. A. Chevalier  D. L. Lambert 《Solar physics》1970,11(2):243-257

The excitation of the 2s²2p² ground configuration of Caxv is calculated for coronal densities and temperatures. The calculations include electron and proton excitation of the forbidden transitions and electron excitation via the first excited (2s2p³) configuration. It is shown that measurements of the line intensity ratio I( 5694)/I( 5446) are in good agreement with the predictions. The line to continuum observations for limb flares and coronal condensations are discussed. It is suggested that the calcium abundance in condensations is enhanced owing to diffusion processes.Present address: Department of Astronomy, University of Texas, Austin, Texas, U.S.A.  相似文献   

Absolute wavelengths of Fraunhofer lines: Convective motions in the solar photosphere and the gravitational red shift     

D. L. Lambert  E. A. Mallia 《Solar physics》1968,3(4):499-504

Absolute wavelengths for Fraunhofer lines are compared with laboratory measurements for several atomic and molecular spectra. The wavelength differences are shown to be consistent with the proposal that the deeper layers of the photosphere are in convective motion: _e -3 km/sec for log ₀> -1.0. Convective motions in the outer layers (log₀< - 1.0) are shown to be very small. Wavelength shifts of Fraunhofer lines formed in these outer layers are in good quantitative agreement with the predictions of the General Theory of Relativity.  相似文献   

Combining geomorphological and geodetic data to determine postglacial tilting in Manitoba     

A. Lambert  T. S. James  L. H. Thorleifson 《Journal of Paleolimnology》1998,19(3):365-376

Estimates of postglacial rebound in central North America from Laurentide deglaciation to the present time are uncertain as a result of lack of data from the continental interior. A more precise knowledge of postglacial tilt history will assist studies of the evolution of the major lakes in Manitoba and will facilitate the engineering and environmental management of the present-day hydrological system. This paper explores the benefits of combining geomorphological data with high-precision, real-time geodetic data (GPS positioning and absolute gravity) and lake-gauge tilt data now being collected for postglacial rebound studies in Manitoba and adjacent regions in the US. Presently-available data sets representing these data types are (1) tilting of the 9.5 kyr B.P. Campbell strand line south and west of Lake Winnipeg, (2) the rate of decrease in absolute gravity values measured from 1987 to 1995 at Churchill, Manitoba, and (3) the present-day regional tilt rate derived from water-level gauges in southern Manitoba lakes. These data are compared to theoretical predictions based on the published ICE-3G loading history and on a model of Earth rheology characterized by a 1066B density and elastic structure, an upper-mantle viscosity of 10 ²¹Pa s, a lower-mantle viscosity of 2 × 10 ²¹Pa s, and a lithosphere thickness of 120 km (Tushingham & Peltier, 1991). All three data types show disagreement in Manitoba with ICE-3G and the standard Earth model. ICE-4G does better but could not be investigated in any detail. The constraints on model parameters provided by the different data types were investigated by varying, one at a time, three key parameters, (1) the thickness of the lithosphere in excess of 120 km, (2) the lower mantle viscosity, and (3) the thickness of Laurentide ice over the Prairies, to obtain better fits to the data. The present data do not appear to constrain lithosphere thickness in excess of 120 km very well. While both the Campbell strand line data and the Churchill absolute gravity data are consistent with an increase in lower-mantle viscosity, the present-day, lake-gauge data are not. All three data types are consistent with a thinning of the Laurentide ice-sheet over the Prairies relative to the ICE-3G model. Simultaneous adjustment of model parameters with the advantage of anticipated new data in Manitoba and adjacent regions in the US will lead to better understanding of the trade-offs between Earth rheology and ice sheet history and hence to an improved Laurentide postglacial rebound model.  相似文献   

Performance and accuracy of a GRAPE-3 system for collisionless N-body simulations     

Athanassoula  Bosma  Lambert  & Makino 《Monthly notices of the Royal Astronomical Society》1998,293(4):369-380

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Alpha Cygni as a radial-velocity variable     

M. Parthasarathy  David L. Lambert 《Journal of Astrophysics and Astronomy》1987,8(1):51-56

One hundred and twentythree radial velocities for α Cyg are derived between December 1977 and October 1982. These photospheric velocities are derived from N_I lines near 8700 å. Semiregular variations in radial velocities are present with periods of 7 to 20 days. The range of variation of 14.3 kms^?1 observed in the present radial velocities of α Cyg is close to the sum of the amplitudes (10.44 kms^?1) of all the pulsation periods from 7 to 101 days (Lucy 1976a) and is also approximately equal to micro and macro-turbulent velocities.  相似文献   

Anthropogenic vs. lithogenic origins of trace elements (As, Cd, Pb, Rb, Sb, Sc, Sn, Zn) in water column particles: northwestern Mediterranean Sea   总被引：1，自引：0，他引：1  

F. E. Grousset  C. R. Quetel  B. Thomas  O. F. X. Donard  C. E. Lambert  F. Guillard  A. Monaco 《Marine Chemistry》1995,48(3-4)

The distribution of heavy metal was analyzed in water column particles collected in autumn (October 1985) and spring (March 1986) by two series of sediment traps from a mooring located in the northeastern Mediterranean Sea continental slope. Four traps were set, at 50, 100, 300, 600 m depths on the mooring in 645 m deep water in the Lacaze-Duthier canyon. The total metal concentrations were determined by ICP-MS. Results show that Rb and Sc contents display typical shale values. As, Cd, Pb, Sb, Zn (normalized to Sc) display high enrichment factors (up to 50) over shale compositions. Distinctive temporal variability as well as the respective contributions of local (Têt, Aude) and remote (Rhône) rivers and Sahara-derived aerosols have been identified. Fluxes of most elements observed in the upper 100 m can be attributed to atmospheric fluxes. In the deepest traps (300 and 600 m) these fluxes are, however, mostly dominated by riverine particles advected from the continental shelf. Most of the trace-element enrichments are more likely to be related to the anthropogenic input rather than to biological cycling. Isotopic composition of lead determined by ICP-MS enabled to evaluate that the proportion of anthropogenic lead derived from European gasoline consumption ranged between 50 and 100%.  相似文献   

Observation of the Earth’s nutation by the VLBI: how accurate is the geophysical signal     

César Gattano  Sébastien B. Lambert  Christian Bizouard 《Journal of Geodesy》2017,91(7):849-856

We compare nutation time series determined by several International VLBI Service for geodesy and astrometry (IVS) analysis centers. These series were made available through the International Earth Rotation and Reference Systems Service (IERS). We adjust the amplitudes of the main nutations, including the free motion associated with the free core nutation (FCN). Then, we discuss the results in terms of physics of the Earth’s interior. We find consistent FCN signals in all of the time series, and we provide corrections to IAU 2000A series for a number of nutation terms with realistic errors. It appears that the analysis configuration or the software packages used by each analysis center introduce an error comparable to the amplitude of the prominent corrections. We show that the inconsistencies between series have significant consequences on our understanding of the Earth’s deep interior, especially for the free inner core resonance: they induce an uncertainty on the FCN period of about 0.5 day, and on the free inner core nutation (FICN) period of more than 1000 days, comparable to the estimated period itself. Though the FCN parameters are not so much affected, a 100 % error shows up for the FICN parameters and prevents from geophysical conclusions.  相似文献   

Comparison of high-resolution seismic profiles and the geoacoustic properties of Eckernförde Bay sediments     

Niall C. Slowey  William R. Bryant  Douglas N. Lambert 《Geo-Marine Letters》1996,16(3):240-248

High-resolution seismic profiles of Eckernförde Bay and the adjacent Baltic Sea were collected, and the geoacoustic properties of sediments there were measured. Bulk densities averaged ~ 1.35 g cm^–3 and ranged from ~ 1.2 to ~ 1.7 g cm^–3. Compressional wave velocities in gas-free sediments averaged ~ 1460 m s^–1 and ranged from ~ 1425 to ~ 1555 m s^–1. In nongassy sediments, bulk density variations typically controlled changes of acoustic impedance. Impedance changes were usually too small and closely spaced to be resolved seismically, although, at certain sites, significant impedance changes are far apart enough that they correlate one-to-one with seismic reflectors. Where free gas is present, velocity decreases and wave energy is scattered, causing a prominent seismic reflector.  相似文献