摘要:

Hydrocarbon impregnated fenestral dolomites of the Phosphoria Formation were sampled on both flanks of Sheep Mountain Anticline, Wyoming. Demagnetization results indicate one dominant component that is either synfolding (Laramide in age) or predates folding (Cretaceous in age). Thermal demagnetization yields stable decay to temperatures between 500°C and 550°C and rock magnetic experiments suggest that the magnetization is dominated by a low coercivity component. Magnetic extracts contain spheres (<15 µ diameter) as well as other authigenic forms. Energy dispersive analysis demonstrates that Fe is the only detectable element present in the spheres and X‐ray diffraction analysis indicates that magnetite is present in the extracts; the spheres are interpreted to be authigenic magnetite. The magnetization is interpreted as a chemical remanent magnetization (CRM) residing in this authigenic magnetite. Chemical conditions created by the hydrocarbons may have caused precipitation of the authigenic magnetite and acquisition of the associated

ISSN:0094-8276    

DOI:10.1029/GL014i004p00323

年代:1987

数据来源: WILEY

摘要:

Thermal demagnetization characteristics of a Brunhes‐age viscous overprint in Appalachian redbeds and a thermoviscous component acquired in the laboratory at moderate temperature agree well with relaxation time‐blocking temperature relations for hematite proposed by Pullaiah et al. [1975]. Supporting evidence was obtained from redbeds associated with an igneous dike intrusion although the interpretation of these data are complicated by magnetochemical alterations. Paradoxically, experimental data for magnetite in some limestones were shown to agree more closely with an alternative theory of Walton [1980]. The hematite in redbeds is predominantly singledomain (SD) whereas magnetite in the limestones studied extends well into the multidomain (MD) range. Thus experiment and theory could be reconciled if it is assumed that Pullaiah et al. applies strictly to SD material whereas Walton's theory somehow describes thermoviscous effects dominated by larger MD gra

ISSN:0094-8276    

DOI:10.1029/GL014i004p00327

年代:1987

数据来源: WILEY

摘要:

Rock, when fractured in the laboratory, emits electrical signals with a broad maximum in the power density spectrum in the band from 900 Hz to 5 kHz. Quartz‐free basalt rocks radiate both light and low‐frequency electrical signals as intensely as quartz‐bearing rocks, suggesting that the piezoelectric effect of quartz is at most a minor contributor to the total power radiated. Newly created rock surfaces acquire a local net charge distribution when exoelectrons are expelled and removed from the vicinity of the new surfaces by collisional and other processes. The rotational, vibrational, and linear motion of rock fragments with charged surfaces is the major contributor to the observed power density spectrum of the low‐frequency electrical signals. Neither optical spectral lines nor high‐frequency electromagnetic radiation, characteristic of electric discharges, occur at fracture. Exoelectron bombardment of the ambient fluid surrounding the sample, not electric discharge, is the excitation source for the light emitted at

ISSN:0094-8276    

DOI:10.1029/GL014i004p00331

年代:1987

数据来源: WILEY

摘要:

Internal heating and secular cooling are expected to decrease the geothermal gradient away from an adiabat. A scaling analysis that is quantified on the basis of published numerical models indicates that the interior geotherm should be nearly isothermal through the lower mantle if all heating is from within. For the more realistic condition that the mantle is partly heated from within and partly from below, we still expect the average thermal gradient to be significantly subadiabatic through much of the interior of the mantle. Values of the seismologically observable inhomogeneity parameter η ∼ 1.04 to 1.07 should characterize the subadiabatic regions of the lower mant

ISSN:0094-8276    

DOI:10.1029/GL014i004p00335

年代:1987

数据来源: WILEY

摘要:

Earthquakes that occur within the Nazca plate subduction zone tend to fall into two populations: the generally smaller, nearly pure double‐couple events, and the usually larger, non‐double‐couple earthquakes. In fact, there appears to exist a direct relationship between the proportion of the non‐double‐couple component in the earthquake solution and the scalar moment. A similar trend is not observed on the global scale. Furthermore, most of the earthquakes with large non‐double‐couple components occur in the locations where the greatest amount of structural complexity is expected. We therefore hypothesize that the non‐double‐couple mechanisms in this region are, in general, related to the break‐down of the assumption of slip on a planar fault‐surface, one of the fundamental assumptions in obtaining moment tensor source mechanisms in accord with the double‐couple model. This failure is, in turn, related to the extreme structural co

ISSN:0094-8276    

DOI:10.1029/GL014i004p00339

年代:1987

数据来源: WILEY

摘要:

To improve the lateral resolution of 3 dimensional models of seismic wave velocities in the Indian Ocean and surrounding regions we analyzed direct earthquake to station Rayleigh waves observed on the vertical long‐period components of four GEOSCOPE stations [TAM (Algeria), PCR (La Réunion), PAF (Kerguelen) and AGR (Djibouti)].The phase velocities along 51 well‐distributed paths are obtained in the period range 40‐350 s after corrections for the phase pattern at the source and for the instrumental response. A tomographic method is then applied (Montagner, 1986a) to compute the geographical distribution of phase velocities, without any a priori regionalization.The location of velocity anomalies is quite stable and well resolved. The phase velocity distributions are compared with global results from Nakanishi and Anderson (1984b), Woodhouse and Dziewonski (1984), Tanimoto (1985), Nataf et al. (1986) and with regional studies using group velocities for the same region (Montagner, 1986

ISSN:0094-8276    

DOI:10.1029/GL014i004p00343

年代:1987

数据来源: WILEY

摘要:

Earthquakes along the southern edge of the Gorda plate and the Mendocino fracture zone that were relocated jointly generally tend to move 25 to 35 km southwest of their PDE and ISC locations. This has the effect of reducing the number of events occurring deep in the plate and increasing the number of events located on the Gorda rise as well as revealing a tightly grouped linear zone of activity extending along the Mendocino fracture zone. The resulting spatial pattern of seismicity is more consistent with recent models of the tectonics of the Gorda plate and the Mendocino fracture zone.

ISSN:0094-8276    

DOI:10.1029/GL014i004p00347

年代:1987

数据来源: WILEY

摘要:

A method proposed by Salby for computing space‐time Fourier transforms of asynoptic satellite data has been applied to stratospheric brightness temperature measurements from January and February 1979 in a search for two fast‐moving low‐wavenumber instabilities predicted in a numerical study by Lynch. The method is capable of producing spectra down to periods of approximately one day with no distortion due to the asynopticity of the data. No spectral peaks corresponding to the predicted modes were found; taking the noise level as the upper limit for their amplitudes at the altitudes observed, an upper limit of approximately 0.6 to 1.2 degrees Kelvin may be set for their peak amplitudes near the meso

ISSN:0094-8276    

DOI:10.1029/GL014i004p00351

年代:1987

数据来源: WILEY

摘要:

Fast coronal mass ejecta interact strongly with the ambient interplanetary plasma and magnetic field into which they propagate. A shock forms in front of an ejection and the slower moving ambient plasma ahead is accelerated and deflected from its path. In this paper we argue that such flow accelerations and deflections of the ambient plasma must produce a draping of the ambient interplanetary magnetic field about the ejected material similar to that which occurs in the magnetosheath surrounding the earth's magnetosphere. The draping pattern should depend upon the overall size and shape of the ejection, its speed relative to the ambient plasma ahead, the orientation of the ambient magnetic field, and the position where the shocked plasma is sampled. At some locations upstream from an ejection draping leads to an enhancement of the out‐of‐the‐ecliptic field component (BZ) at the expense of the ecliptic components (BX, BY). Although turbulence and fluctuations in the ambient field may confuse the observational situation, we suggest that draping probably plays an important role in producing intervals of strong and prolonged negative BZin the ecliptic plane at 1 AU and thus also may be an important factor in stimulating geomagnetic act

ISSN:0094-8276    

DOI:10.1029/GL014i004p00355

年代:1987

数据来源: WILEY

摘要:

Results are presented from a Spherical Retarding Potential Analyzer (SRPA) and a spherical Langmuir Probe (LP) which were flown on the Spacelab‐2 (SL‐2) mission of the Space Shuttle Orbiter in August, 1985. The probes were mounted in such a position that for certain Orbiter orientations, the wake edge formed by the starboard payload bay sill swept across the probes at a roll rate of once per orbit about an inertially stabilized pointing direction. Profiles of O+number density and electron number density across the wake edge showed that, after correction for the spatial separation of the sensors, the charge particle number densities declined into the wake at a faster rate than that predicted by theoretical models. At angles of more than 10° into the wake from its geometric edge we find two electron populations having different mean random energies and electrical potentials. One of these populations is suggested to be the result of selective filtering of the high energy tails of the ambient ionospheric population, the other a result of photo‐emission from the payload bay su

ISSN:0094-8276    

DOI:10.1029/GL014i004p00359

年代:1987

数据来源: WILEY