摘要:

Mean relativePwave (1 s) amplitude characteristics are determined for standardized seismic stations in the United States. Data are compiled from three azimuths: to the north, explosions in Russia; to the northwest, earthquakes along the Asian‐Pacific arc; and to the south‐southeast, earthquakes in South America. Characteristic receiver amplitudes are found to be azimuthally dependent. High‐amplitude areas occur in the central United States, and lowest amplitudes occur along the Rocky Mountain front range and the Rio Grande rift zone. Amplification effects of low‐velocity sediments are significant in the central United States. Azimuthal amplitude variations in the eastern United States are consistent with an anomalous attenuating or defocusing body in the lower mantle beneath Colombia, South America. Nonazimuthal amplitude studies are tied to the azimuthal data set to increase station amplitude coverage. The regional and local stability of amplitudes is analyzed. Amplitudes are stable with an average variation of a factor of about 1.3 around the regional mean. For seismic stations situated on hard bedrock, the squared amplitude variations are related to energy variations in thePwave fronts. Acknowledging the likely importance of elastic focusing/defocusing and scattering effects at individual stations, variations of anelastic attenuation are derived that are consistent with the observed energy‐amplitude variations. Assuming that the variations of anelastic attenuation occur in the upper 400 km of the earth, high‐amplitude stations may be unattenuated, low‐amplitude stations are consistent withQ∼ 110, and a mean amplitude impliesQ∼ 220–240. The range of variation ofQis mapped into temperature variations, assuming a thermally activatedQmechanism and an olivine activation energy for the upper mantle. The apparentQvariations are consistent with temperature variations of 135°–287°C between high‐ and low‐amplitude seismic station sites. Geophysical and physiographic correlations with thePwave amplitude variations are discussed. Accounting for the motion of the North American plate, lowPwave amplitudes along the Rocky Mountain front may be related to the uplift of the Colorado Plateau. Low amplitudes extending from northern Texas to New England lie along the approximate boundar

ISSN:8755-1209    

DOI:10.1029/RG022i001p00001

年代:1984

数据来源: WILEY

摘要:

Wüstite is a complex nonstoichiometric oxide of iron with the general structural formulaVI[Fe2+1−3xFe3+2x−t□x+t]IVFe3+tO where 0.04

ISSN:8755-1209    

DOI:10.1029/RG022i001p00037

年代:1984

数据来源: WILEY

摘要:

Most of the paleomagnetic data available from oceanic plates consist of measurements of inclination but not declination from azimuthally unoriented vertical cores. Similarly, the basic paleomagnetic data to be analyzed from crustal blocks that have rotated by varying amounts about vertical axes are a set of paleoinclinations. A new method is proposed for determining the paleocolatitude of a sampling site and the associated confidence limits. Paleomagnetic inclinations are first converted to paleocolatitudes and averaged to produce a mean colatitude. After showing that this mean is biased, we derive a paleocolatitude correction to remove the bias, using a model for geomagnetic secular variation based on the latitude dependence of secular variation during the past 5 million years. After testing the validity of the model by applying it to paleomagnetic data from Quaternary lavas for which both inclination and declination are known, we apply the method to inclination‐only paleomagnetic data from Suiko Seamount, the most complete data set from a drilling site. The method is then applied to paleomagnetic data from all Deep Sea Drilling Project sites for the Pacific plate to obtain for each site an unbiased mean paleocolatitude and its confidence limits. These paleocolatitudes and confidence limits are then used as input for a least squares analysis to obtain Early and Late Cretaceous poles for the Pacific plate and 95% confidence limits for these poles. It is shown that the scatter of individual site paleocolatitudes about the best fit pole is consistent with the confidence limits at each site as determined by the new method of analysi

ISSN:8755-1209    

DOI:10.1029/RG022i001p00047

年代:1984

数据来源: WILEY

摘要:

Dissipation of tidal energy is expressed here as an integral on the surface of a sphere that encloses the mass of the planet. When developed in constituent form, this surface integral depends linearly on the secondary potential that arises from the tidal disturbance; it can therefore be expressed as the sum of one part due to the body tide and another due to the fluid tides. The body tide part depends only on the anelastic response of the solid earth to the primary potential. The fluid tide part depends mainly on the elastic solid earth response to tidal loading and on the sum of the ocean tide and atmospheric tide mass disturbances. The atmosphere's contribution can be evaluated reliably from published analyses of the observed barometric tide. Tide gage data, on the other hand, do not suffice for a comparably reliable analysis of the observed ocean tide and must therefore be supplemented by dynamical interpolation through numerical integration of Laplace's tidal equations. Dissipation obtained from ocean tide models published during the past 5 years has a range of at least ±15% from the average value. The main cause of this uncertainty is the difficulty of modeling dissipation, but there are other uncertain aspects of existing models, notably the lack of provision for absorption of energy into baroclinic motions and for the anelastic response of the solid earth to tidal loading

ISSN:8755-1209    

DOI:10.1029/RG022i001p00073

年代:1984

数据来源: WILEY

摘要:

The Scandinavian Twin Auroral Radar Experiment (STARE) has proved useful in estimating the ionospheric electric fields of several types of ULF pulsation. These usually involve the propagation of hydromagnetic waves along the geomagnetic field lines. Reflection at the auroral ionosphere boundary can then result in standing wave resonances. Because of its good spatial resolution and coverage of this boundary, STARE provides unique data on the spatial variations of the pulsation fields. Background theoretical aspects and STARE observations are presented for three types of pulsation: impulsive or ringing Pc 5, monochromatic resonant Pc 5, and pulsations thought to be generated by instabilities in the ring current particle population. Since the ionosphere is resistive, it acts as an energy sink for the pulsations, and estimates of the ionospheric Joule heating are presented. Finally, some suggestions for future work are given.

ISSN:8755-1209    

DOI:10.1029/RG022i001p00085

年代:1984

数据来源: WILEY

ISSN:8755-1209    

DOI:10.1029/RG022i001p00098

年代:1984

数据来源: WILEY

ISSN:8755-1209    

DOI:10.1029/RG022i001p00099

年代:1984

数据来源: WILEY