Short-period PKP phases and the anelastic mechanism of the inner core     

Vernon F. Cormier 《Physics of the Earth and Planetary Interiors》1981,24(4):291-301

Short-period seismograms are synthesized for PKP phases in anelastic Earth models. The synthetics were constructed using a synthetic technique valid at grazing incidence, a source-time function appropriate for deep-focus earthquakes, and an instrument response for either a short-period WWSSN or SRO seismograph. The agreement between predicted and observed amplitudes and spectral ratios requires neither a low-Q_α zone at 0.2–2 Hz nor a low or negative P-velocity gradient at the bottom of the outer core. Thin low-Q_α zones beneath the inner core boundary fit spectral ratio data that sample the upper 200 km of the inner core but fail to fit data that sample the lower inner core. Only a model having Q_α^?1?[0.003, 0.004] at 0.2–2 Hz, nearly constant with depth in the inner core, satisfies all of the spectral ratio and amplitude data. The assumption of a bulk viscosity of 10-10³ Pa s for the liquid phase of a partially molten inner core combined with the observation of low shear attenuation in the inner core at frequencies less than 0.005 Hz limit the physical parameters associated with two possible attenuation mechanisms: (1) fluid flow and viscous relaxation due to ellipsoidally shaped inclusions of melt, and (2) the solid-liquid phase transformation induced by the stress change during the passage of a seismic wave. Both mechanisms require an order of 0.1% partial melt to reproduce the observed Q_α^?1. In the outer core, the time constant of the mechanism of phase transformation is predicted to be 10⁴–10⁶ s. Confirmation of small shear attenuation in the inner core in the frequency band of seismic body waves would favor the mechanism of phase transformation.  相似文献   

Interpretation of metamorphic assemblages containing fibrolitic sillimanite     

R. H. Vernon  R. H. Flood 《Contributions to Mineralogy and Petrology》1977,59(3):227-235

Microstructural criteria distinguish two types of fibrolitic sillimanite-bearing aggregates, namely: (1) those with fibrolitic sillimanite in clear microstructural equilibrium with the other minerals, and (2) those with fibrolitic sillimanite that appears to have grown without evident modification of pre-existing grain boundaries of the other minerals. However, microstructural criteria rarely permit unambiguous inferences of the relative timing of metamorphic reactions producing fibrolitic sillimanite.  相似文献   

Surveying Infrasonic Noise on Oceanic Islands     

M. A. H. Hedlin  J. Berger  F. L. Vernon 《Pure and Applied Geophysics》2002,159(5):1127-1152

v--vAn essential step in the establishment of an International Monitoring System (IMS) infrasound station is the site survey. The survey seeks a location with relatively low infrasonic noise and the necessary logistical support. This paper reports results from our surveys of two of the oceanic sites in the IMS - the Azores and Cape Verde. Each survey sampled infrasonic noise, wind velocity, air temperature and humidity for ~3 weeks at 4 sites near the nominal IMS locations. The surveys were conducted on Sao Miguel (the main island in the Azores) and Maio (Cape Verde). Infrasonic noise was measured using the French MB2000 microbarometer.¶During our 3-week experiment in January the trade winds at Cape Verde varied little from an azimuth of 63°. Because of the unvarying wind azimuth, the experiment gave us an opportunity to examine the effectiveness of a forest at reducing both wind speed and infrasonic noise. We find that the thick Acacia forest on Maio reduces wind speeds at a 2 m elevation by more than 50% but does not reduce infrasonic noise at frequencies below 0.25 Hz. This forest serves as a high-frequency filter and clearly does not reduce long-period noise levels which are due to large-scale turbulence in the atmospheric boundary layer above the forest. This is consistent with our observations in the Azores where the relationship between infrasonic noise and wind speed is more complex due to frequent changes in wind azimuth.¶In Cape Verde, wind speed and infrasonic noise are relatively constant. The diurnal variations are clearly seen however the microbarom is only rarely sensed. In the Azores, during our 3-week experiment in November and December of 1998, wind speed and infrasonic noise change rapidly. At this location, daily noise level swings of 40 to 50 dB at 0.1 Hz are not uncommon in the early winter and are due to changes in wind speed and atmospheric turbulence. The effectiveness of an infrasound station in the Azores will be strongly dependent on time during the winter season.¶The two surveys illustrate some of the difficulties inherent in the selection of sites for 1 to 3 km aperture arrays on oceanic islands. Due to elevated noise levels at these sites, 8 element, 2 km aperture arrays are strongly preferred.  相似文献   

Book reviews     

Vernon F. Cormier  Gregory A. Houseman  David F. McTigue  Manfred Koch  William L. Power  Marek Lewandowski  Chris J. Marone  Carlo Denis  Brian F. Farrell  Timothy J. Fuller-Rowell 《Pure and Applied Geophysics》1993,140(4):729-754

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Ozone measurements from the Balloon Intercomparison Campaign     

D. Robbins  J. Waters  P. Zimmermann  R. Jarnot  J. Hardy  H. Pickett  S. Pollitt  W. Traub  K. Chance  N. Louisnard  W. Evans  J. Kerr 《Journal of Atmospheric Chemistry》1990,10(2):181-218

Measurements of the Balloon Intercomparison Campaign (BIC), conducted during fall, 1982 (BIC-1) and summer, 1983 (BIC-2), are reported. Results of five remote and two in situ techniques agree (with a few exceptions) within 95% confidence level uncertainties and generally within 15% above 20 km. Weighted mean profiles, which best represent conditions during the capaign, are used as a comparison standard. Accuracies of experiments indicated by BIC generally confirm estimated uncertainites for ECC sondes, UV photometry, and microwave emission experiments, are somewhat better for far IR emission and IR absorption experiments, and are somewhat worse for IR emission and solar UV absorption experiments. The large collection of BIC measurements confirms a problem reported earlier with current theoretical modeling of ozone near 40 km where transport is negligible and the chemistry is believed to be simpler.  相似文献   

Critical issues for long-term climate monitoring     

Karl  Thomas R.  Derr  Vernon E.  Easterling  David R.  Folland  Chris K.  Hofmann  David J.  Levitus  Sydney  Nicholls  Neville  Parker  David E.  Withee  Gregory W. 《Climatic change》1995,31(2-4):185-221

Climatic Change - Even after extensive re-working of past data, in many instances we are incapable of resolving important aspects concerning climate change and variability. Virtually every...  相似文献   

How deceptive are microstructures in granitic rocks? Answers from integrated physical theory,phase equilibrium,and direct observations     

M.?B.?HolnessEmail author  J.?D.?Clemens  R.?H.?Vernon 《Contributions to Mineralogy and Petrology》2018,173(8):62

In this contribution, we address the vexed question of the extent to which microstructures in granitic rocks reflect their igneous histories or have been masked by later events. The previous works have tended to address the problem either using theoretical or modelling considerations, or by interpretation of observed microstructures. Here, we use an approach that integrates the theory of microstructural development and the results of experimental phase-equilibrium studies with direct observation of natural examples on a variety of scales. We show that the predictions of the theoretical and experimental approaches agree perfectly with the mesoscopic and microscopic evidence from granitic rocks themselves. Our conclusion is that although, in many cases, granitic rock microstructures have been modified by near-solidus reactions and crystallisation, in the absence of tectonic deformation the fundamental elements of their igneous heritage remain intact. This means that it is perfectly in order to infer aspects of crystallisation sequences, magmatic reactions, and magma flow through careful microstructural observations. Thus, our answer to the question of how deceptive granitic textures are is, in most instances, ‘not very’. However, some undeformed plutons have undergone fluid-driven alteration, and others have been affected by contact metamorphism. Thus, each case should be examined on its own merits.  相似文献   

Summer field meeting to North-East Yorkshire: August 9th to 20th, 1934     

Maurice Black  J.E. Hemingway  Vernon Wilson 《Proceedings of the Geologists' Association. Geologists' Association》1934,45(3):291-IN6

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Full scale wake and boundary layer instrumentation feasibility study     

Vernon A. Phelps  Research Scientist  Project Director  Armin W. Troesch  Assistant Research Scientist  John P. Hackett  Graduate Research Assistant 《Ocean Engineering》1980,7(2):281-304

Fluid-flow measuring devices intended for full scale use were designed and tested. One device consisted of a rake supporting different types of pitot tubes. This will be used to obtain a velocity profile of the boundary layer of a test ship. The other device was a five-hole pitot tube that was used in a wake survey. The pressure transport medium (i.e. the medium that carried the pressure signal from the pitot tube to the pressure transducer) was air instead of water. This proved to be successful, as the results indicate.  相似文献   

How late are K-feldspar megacrysts in granites?   总被引：1，自引：0，他引：1  

R.H. Vernon  S.R. Paterson 《Lithos》2008,104(1-4):327-336

Various petrologists have suggested that K-feldspar megacrysts grow in granites that are extensively crystallized, even at subsolidus conditions. However, experimental evidence indicates that, though K-feldspar nucleates relatively late in the crystallization history, abundant liquid is available for development of large crystals. A great deal of evidence, involving many different factors, favours a magmatic/phenocrystic origin for K-feldspar megacrysts in granites, namely simple twinning, oscillatory zoning, euhedral plagioclase inclusions, and concentric, crystallographically controlled arrangements of inclusions. In addition, abundant evidence has been presented of (1) mechanical accumulation of K-feldspar megacrysts in granites, (2) alignment of megacrysts and megacryst concentrations in magmatic flow foliations, (3) involvement of megacrysts in zones of magma mixing in granite plutons, and (4) occurrence of megacrysts in some volcanic rocks, implying that the megacrysts were suspended in enough liquid to be moved without fracturing or plastic deformation. Detailed trace element and isotopic data also indicate that megacrysts can move between coexisting felsic and more mafic magmas. Irregular overgrowths on megacrysts are consistent with continued magmatic growth after euhedral megacrystic growth ceased, the overgrowths being impeded by simultaneously crystallizing quartz and feldspar grains.  相似文献