Genesis of marine terrace soils,Barbados, West Indies: Evidence from mineralogy and geochemistry     

Daniel R. Muhs  Russell C. Crittenden  John N. Rosholt  Charles A. Bush  Kathleen C. Stewart 《地球表面变化过程与地形》1987,12(6):605-618

Well-developed, clay-rich soils dominated by interstratified kaolinite-smectite are found on the uplifted coral reef terraces on the island of Barbados. The reef limestone is unlikely to have been the soil parent material however, because it is 98 per cent CaCO₃ and geomorphic evidence argues against the 20 m of reef solution required to produce the soils by this process. The mineralogy of the sand, silt, and clay fractions of the soils, and trace element geochemistry, suggest that aeolian materials carried on the trade winds from Africa, volcanic ash from the island of St. Vincent, and quartz from Tertiary bedrock on the island itself are the parent materials for the soils.  相似文献   

Remote sensing of the ocean     

W. H. Munk  J. D. Woods  W. P. Birkemeier  C. G. Little  R. H. Stewart  J. Richter 《Boundary-Layer Meteorology》1973,5(1-2):201-209

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On the prediction of turbulence in baroclinic zones     

Kenneth R. Hardy  Madoka Fukushima  Peter F. Lester  Robert H. Stewart 《Boundary-Layer Meteorology》1973,5(1-2):245-250

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Replenished magma chambers: effects of compositional zonation and input rates     

Herbert E. Huppert  J. Stewart Turner  R. Stephen  J. Sparks 《Earth and Planetary Science Letters》1982,57(2):345-357

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Complexity of rupture in large strike-slip earthquakes in Turkey     

Gordon S. Stewart  Hiroo Kanamori 《Physics of the Earth and Planetary Interiors》1982,28(1):70-84

Complexity of rupture propagation has an important bearing on the state of stress along the earthquake fault plane and on the prediction of strong ground motion in the near-field. By studying far-field body waveforms recorded by WWSSN long-period seismograms it has been possible to investigate the degree of complexity of several Turkish earthquakes. The results, which are obtained by matching synthetic P waveforms to observed data indicate that the July 22, 1967 Mudurnu Valley earthquake (M_s = 7.1) is a complex event which can be explained by the superposition of elementary sources with variable amplitudes and source time sequence history. In this regard, it is very similar to the February 4, 1976 Guatemala earthquake (M_s = 7.5). A comparison of these two events indicates that their source-time series ranges from 5 to ca. 20 s and, regardless of the total moment of the earthquake, the moment of the individual events is bounded at around 5 × 10²⁶ dyn cm. The November 24, 1976 E. Turkey earthquake (M_s = 7.3), on the other hand, has a complexity which cannot be explained by such a simple model; in this respect, it may be more similar to the Tangshan, China, earthquake and as such, may involve significant thrust, normal or other complications to its faulting mechanism than the strike-slip mechanism of the P-wave first-motion data. The source time history for the 1967 Mudurnu Valley event is used to illustrate its significance in modeling strong ground motion in the near field. The complex source-time series of the 1967 event predicts greater amplitudes (2.5 larger) in strong ground motion than a uniform model scaled to the same size for a station 20 km from the fault. Such complexity is clearly important in understanding what strong ground motion to expect in the near-field of these and other continental strike-slip faults such as the San Andreas.  相似文献   

Slow earthquakes along oceanic fracture zones: evidence for asthenospheric flow away from hotspots?     

Emile A. Okal  Lisa M. Stewart 《Earth and Planetary Science Letters》1982,57(1):75-87

The regime of strain release along transform faults of the Mid-Oceanic Ridge system is studied. It is shown that earthquakes along certain fracture zones exhibit systematic discrepancies between values of their magnitudes measured at short and long periods, implying a regime of slower strain release, also observed in a pattern of complex body waveshapes. These “slow” fracture zones do not correlate with simple geographic or kinematic properties, but usually occur in the neighborhood of hotspot volcanism, frequently also characterized by gravity and bathymetry anomalies. We propose that regimes of slow strain release may be due to a partial lubrication of the fault along these fracture zones, which may itself be due to asthenospheric flow from the nearby hotspots, along the pattern of pipelines described by Vogt and Johnson and by Morgan.  相似文献   

Application of Resistivity Surveys to Regional Hydrogeologic Reconnaissance   总被引：2，自引：0，他引：2  

Mark Stewart  Michael Layton  Theodore Lizanec 《Ground water》1983,21(1):42-48

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A negative search for an ultra-slow component to the source of the Yunnan earthquakes of May 29, 1976     

Emile A. Okal  Lisa M. Stewart 《Physics of the Earth and Planetary Interiors》1981,26(3):208-216

Following Nagamune's suggestion of a giant, but very slow, component to the source of the Yunnan earthquakes of May 29, 1976, a systematic study of the ultra-low frequency content of a number of tiltmeter, strainmeter, and IDA records of the events is conducted. First, Nagamune's hypothesis is quantified, and it is found that it would require a moment in the range 10²⁹–10³⁰ dyn-cm. Such a large moment would have important consequences for our understanding of stress release in the plates, but is incompatible with the extent of the aftershock zone, and with observations on other instruments: specifically, only one IDA record shows a time-domain oscillation which may be related to the proposed source. In the Fourier domain, however, a spectral analysis fails to identify any of the Earth's modes in any of the available records, including the one originally used by Nagamune. It must therefore be concluded that the apparent signal present in a few records is due to noise—probably of instrumental origin—rather than to an ultra-low-frequency component of the seismic source.  相似文献   

Radio evidence for a delayed acceleration process in solar flares     

K. Kai  H. Nakajima  T. Kosugi  R. T. Stewart  G. J. Nelson  S. R. Kane 《Solar physics》1986,105(2):383-398

Evidence for a delayed acceleration process in solar flares is presented in the form of an analysis of simultaneous observations in microwaves, decimetre and metrewaves, and hard X-rays of six delayed gradual bursts which appear 0.5–1 hr after the strong main bursts have faded. The observed characteristics of the delayed bursts are: (a) similarity of flux time profiles at all the wavelengths, (b) low turn-over frequency (4 GHz) of the microwave spectrum, (c) moderately strong circular polarization (30–40%) and low altitude of the microwave source (which is displaced toward the disk centre by a projected distance of 10–20 from that of the preceding main burst), and (d) low spectral index of the energy spectrum of hard X-rays.From these observations it is suggested that (i) electrons are accelerated up to MeV even some tens of minutes after the impulsive phase acceleration has almost ceased, (ii) the delayed acceleration occurs in a large magnetic structure extending to a height of at least 2 × 10⁵ km, and (iii) the radio source has columnar structure with the microwave source predominantly near a leg or legs and the metrewave source near the top of the magnetic structure. The present observations of the delayed bursts do not seem to be consistent with the classical second-phase acceleration mechanism proposed in the past for normal hard X-ray gradual (extended) bursts.Minamimaki-mura, Minamisaku-gun, Nagano-ken 384-13, Japan.Greenbelt, MD 20771, U.S.A., NASA/NRC Research Associate, on leave from Tokyo Astronomical Observatory.P.O. Box 76, Epping, N.S.W. 2121, Australia.Berkeley, CA 94720, U.S.A.  相似文献   

A multiple-parameter approach to andesitic tephra correlation, Ruapehu volcano, New Zealand     

Shane J. Cronin  Vincent E. Neall  Robert B. Stewart  Alan S. Palmer 《Journal of Volcanology and Geothermal Research》1996,72(3-4)

A multi-parameter approach was used to correlate andesitic tephras in a complex tephra sequence ranging in age from ca. 23 to ca. 75 ka on the eastern ring plain of Ruapehu volcano, North Island. Field properties, combined with ferromagnesian mineral assemblages and mineral compositions, were required to map and correlate this sequence. Three tephra units could be identified based on their unique physical appearance, but other tephras could not be correlated on this basis alone. Hornblende and olivine proved to be valuable marker minerals enabling further distinction of two of the marker units recognised by field properties, as well as defining two further marker tephras. Unweathered titanomagnetite crystals, present in all of the tephras, were subjected to major-element analysis by electron microprobe. Canonical discriminant function analysis (DFA) of these analyses enabled the grouping and discrimination of tephra units, further aiding the identification of defined marker units, as well as defining new marker units. The titanomagnetite chemistry showed a strong relationship to the ferromagnesian mineralogy, showing that the ferromagnesian phenocrysts formed from the same melt or under the same melt conditions prior to eruption of each tephra. Canonical DFA was also applied to hornblende and olivine mineral analyses to identify further marker beds and to confirm identifications of previously defined units. This statistical analysis was found to be invaluable in reducing the large amount of compositional data from this study into a useable form for andesitic tephra correlation and mapping.  相似文献